shithub: candycrisis

ref: d5c86a4701199fa8d1c3f0d8b15d1bd766cbcf6b
dir: /src/support/ibxm.c/

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#include "stdlib.h"
#include "string.h"

#include "ibxm.h"

const char *IBXM_VERSION = "ibxm/ac mod/xm/s3m replay 20191214 (c)mumart@gmail.com";

static const int FP_SHIFT = 15, FP_ONE = 32768, FP_MASK = 32767;

static const int MOD_STEREO_SEPARATION = 50;  // ibxm default was 76.5

static const int exp2_table[] = {
        32768, 32946, 33125, 33305, 33486, 33667, 33850, 34034,
        34219, 34405, 34591, 34779, 34968, 35158, 35349, 35541,
        35734, 35928, 36123, 36319, 36516, 36715, 36914, 37114,
        37316, 37518, 37722, 37927, 38133, 38340, 38548, 38757,
        38968, 39180, 39392, 39606, 39821, 40037, 40255, 40473,
        40693, 40914, 41136, 41360, 41584, 41810, 42037, 42265,
        42495, 42726, 42958, 43191, 43425, 43661, 43898, 44137,
        44376, 44617, 44859, 45103, 45348, 45594, 45842, 46091,
        46341, 46593, 46846, 47100, 47356, 47613, 47871, 48131,
        48393, 48655, 48920, 49185, 49452, 49721, 49991, 50262,
        50535, 50810, 51085, 51363, 51642, 51922, 52204, 52488,
        52773, 53059, 53347, 53637, 53928, 54221, 54515, 54811,
        55109, 55408, 55709, 56012, 56316, 56622, 56929, 57238,
        57549, 57861, 58176, 58491, 58809, 59128, 59449, 59772,
        60097, 60423, 60751, 61081, 61413, 61746, 62081, 62419,
        62757, 63098, 63441, 63785, 64132, 64480, 64830, 65182,
        65536
};

static const short sine_table[] = {
        0,  24,  49,  74,  97, 120, 141, 161, 180, 197, 212, 224, 235, 244, 250, 253,
        255, 253, 250, 244, 235, 224, 212, 197, 180, 161, 141, 120,  97,  74,  49,  24
};

struct note {
    unsigned char key, instrument, volume, effect, param;
};

struct channel {
    struct replay *replay;
    struct instrument *instrument;
    struct sample *sample;
    struct note note;
    int id, key_on, random_seed, pl_row;
    int sample_off, sample_idx, sample_fra, freq, ampl, pann;
    int volume, panning, fadeout_vol, vol_env_tick, pan_env_tick;
    int period, porta_period, retrig_count, fx_count, av_count;
    int porta_up_param, porta_down_param, tone_porta_param, offset_param;
    int fine_porta_up_param, fine_porta_down_param, xfine_porta_param;
    int arpeggio_param, vol_slide_param, gvol_slide_param, pan_slide_param;
    int fine_vslide_up_param, fine_vslide_down_param;
    int retrig_volume, retrig_ticks, tremor_on_ticks, tremor_off_ticks;
    int vibrato_type, vibrato_phase, vibrato_speed, vibrato_depth;
    int tremolo_type, tremolo_phase, tremolo_speed, tremolo_depth;
    int tremolo_add, vibrato_add, arpeggio_add;
};

struct replay {
    int sample_rate, interpolation, global_vol;
    int seq_pos, break_pos, row, next_row, tick;
    int speed, tempo, pl_count, pl_chan;
    int *ramp_buf;
    char **play_count;
    struct channel *channels;
    struct module *module;
};

static int exp_2( int x ) {
    int c, m, y;
    int x0 = ( x & FP_MASK ) >> ( FP_SHIFT - 7 );
    c = exp2_table[ x0 ];
    m = exp2_table[ x0 + 1 ] - c;
    y = ( m * ( x & ( FP_MASK >> 7 ) ) >> 8 ) + c;
    return ( y << FP_SHIFT ) >> ( FP_SHIFT - ( x >> FP_SHIFT ) );
}

static int log_2( int x ) {
    int step;
    int y = 16 << FP_SHIFT;
    for( step = y; step > 0; step >>= 1 ) {
        if( exp_2( y - step ) >= x ) {
            y -= step;
        }
    }
    return y;
}

static char* data_ascii( struct data *data, int offset, int length, char *dest ) {
    int idx, chr;
    memset( dest, 32, length );
    if( offset > data->length ) {
        offset = data->length;
    }
    if( ( unsigned int ) offset + length > ( unsigned int ) data->length ) {
        length = data->length - offset;
    }
    for( idx = 0; idx < length; idx++ ) {
        chr = data->buffer[ offset + idx ] & 0xFF;
        if( chr > 32 ) {
            dest[ idx ] = chr;
        }
    }
    return dest;
}

static int data_s8( struct data *data, int offset ) {
    int value = 0;
    if( offset < data->length ) {
        value = data->buffer[ offset ];
        value = ( value & 0x7F ) - ( value & 0x80 );
    }
    return value;
}

static int data_u8( struct data *data, int offset ) {
    int value = 0;
    if( offset < data->length ) {
        value = data->buffer[ offset ] & 0xFF;
    }
    return value;
}

static int data_u16be( struct data *data, int offset ) {
    int value = 0;
    if( offset + 1 < data->length ) {
        value = ( ( data->buffer[ offset ] & 0xFF ) << 8 )
                | ( data->buffer[ offset + 1 ] & 0xFF );
    }
    return value;
}

static int data_u16le( struct data *data, int offset ) {
    int value = 0;
    if( offset + 1 < data->length ) {
        value = ( data->buffer[ offset ] & 0xFF )
                | ( ( data->buffer[ offset + 1 ] & 0xFF ) << 8 );
    }
    return value;
}

static unsigned int data_u32le( struct data *data, int offset ) {
    unsigned int value = 0;
    if( offset + 3 < data->length ) {
        value = ( data->buffer[ offset ] & 0xFF )
                | ( ( data->buffer[ offset + 1 ] & 0xFF ) << 8 )
                | ( ( data->buffer[ offset + 2 ] & 0xFF ) << 16 )
                | ( ( data->buffer[ offset + 3 ] & 0xFF ) << 24 );
    }
    return value;
}

static void data_sam_s8( struct data *data, int offset, int count, short *dest ) {
    int idx, amp, length = data->length;
    char *buffer = data->buffer;
    if( offset > length ) {
        offset = length;
    }
    if( offset + count > length ) {
        count = length - offset;
    }
    for( idx = 0; idx < count; idx++ ) {
        amp = ( buffer[ offset + idx ] & 0xFF ) << 8;
        dest[ idx ] = ( amp & 0x7FFF ) - ( amp & 0x8000 );
    }
}

static void data_sam_s16le( struct data *data, int offset, int count, short *dest ) {
    int idx, amp, length = data->length;
    char *buffer = data->buffer;
    if( offset > length ) {
        offset = length;
    }
    if( offset + count * 2 > length ) {
        count = ( length - offset ) / 2;
    }
    for( idx = 0; idx < count; idx++ ) {
        amp = ( buffer[ offset + idx * 2 ] & 0xFF ) | ( buffer[ offset + idx * 2 + 1 ] << 8 );
        dest[ idx ] = ( amp & 0x7FFF ) - ( amp & 0x8000 );
    }
}

static int envelope_next_tick( struct envelope *envelope, int tick, int key_on ) {
    tick++;
    if( envelope->looped && tick >= envelope->loop_end_tick ) {
        tick = envelope->loop_start_tick;
    }
    if( envelope->sustain && key_on && tick >= envelope->sustain_tick ) {
        tick = envelope->sustain_tick;
    }
    return tick;
}

static int envelope_calculate_ampl( struct envelope *envelope, int tick ) {
    int idx, point, dt, da;
    int ampl = envelope->points_ampl[ envelope->num_points - 1 ];
    if( tick < envelope->points_tick[ envelope->num_points - 1 ] ) {
        point = 0;
        for( idx = 1; idx < envelope->num_points; idx++ ) {
            if( envelope->points_tick[ idx ] <= tick ) {
                point = idx;
            }
        }
        dt = envelope->points_tick[ point + 1 ] - envelope->points_tick[ point ];
        da = envelope->points_ampl[ point + 1 ] - envelope->points_ampl[ point ];
        ampl = envelope->points_ampl[ point ];
        ampl += ( ( da << 24 ) / dt ) * ( tick - envelope->points_tick[ point ] ) >> 24;
    }
    return ampl;
}

static void sample_ping_pong( struct sample *sample ) {
    int idx;
    int loop_start = sample->loop_start;
    int loop_length = sample->loop_length;
    int loop_end = loop_start + loop_length;
    short *sample_data = sample->data;
    short *new_data = calloc( loop_end + loop_length + 1, sizeof( short ) );
    if( new_data ) {
        memcpy( new_data, sample_data, loop_end * sizeof( short ) );
        for( idx = 0; idx < loop_length; idx++ ) {
            new_data[ loop_end + idx ] = sample_data[ loop_end - idx - 1 ];
        }
        free( sample->data );
        sample->data = new_data;
        sample->loop_length *= 2;
        sample->data[ loop_start + sample->loop_length ] = sample->data[ loop_start ];
    }
}

/* Deallocate the specified module. */
void dispose_module( struct module *module ) {
    int idx, sam;
    struct instrument *instrument;
    free( module->default_panning );
    free( module->sequence );
    if( module->patterns ) {
        for( idx = 0; idx < module->num_patterns; idx++ ) {
            free( module->patterns[ idx ].data );
        }
        free( module->patterns );
    }
    if( module->instruments ) {
        for( idx = 0; idx <= module->num_instruments; idx++ ) {
            instrument = &module->instruments[ idx ];
            if( instrument->samples ) {
                for( sam = 0; sam < instrument->num_samples; sam++ ) {
                    free( instrument->samples[ sam ].data );
                }
                free( instrument->samples );
            }
        }
        free( module->instruments );
    }
    free( module );
}

static struct module* module_load_xm( struct data *data, char *message ) {
    int delta_env, offset, next_offset, idx, entry;
    int num_rows, num_notes, pat_data_len, pat_data_offset;
    int sam, sam_head_offset, sam_data_bytes, sam_data_samples;
    int num_samples, sam_loop_start, sam_loop_length, amp;
    int note, flags, key, ins, vol, fxc, fxp;
    int point, point_tick, point_offset;
    int looped, ping_pong, sixteen_bit;
    char ascii[ 16 ], *pattern_data;
    struct instrument *instrument;
    struct sample *sample;
    struct module *module = calloc( 1, sizeof( struct module ) );
    if( module ) {
        if( data_u16le( data, 58 ) != 0x0104 ) {
            strcpy( message, "XM format version must be 0x0104!" );
            dispose_module( module );
            return NULL;
        }
        data_ascii( data, 17, 20, module->name );
        delta_env = !memcmp( data_ascii( data, 38, 15, ascii ), "DigiBooster Pro", 15 );
        offset = 60 + data_u32le( data, 60 );
        module->sequence_len = data_u16le( data, 64 );
        module->restart_pos = data_u16le( data, 66 );
        module->num_channels = data_u16le( data, 68 );
        module->num_patterns = data_u16le( data, 70 );
        module->num_instruments = data_u16le( data, 72 );
        module->linear_periods = data_u16le( data, 74 ) & 0x1;
        module->default_gvol = 64;
        module->default_speed = data_u16le( data, 76 );
        module->default_tempo = data_u16le( data, 78 );
        module->c2_rate = 8363;
        module->gain = 64;
        module->default_panning = calloc( module->num_channels, sizeof( unsigned char ) );
        if( !module->default_panning ) {
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->num_channels; idx++ ) {
            module->default_panning[ idx ] = 128;
        }
        module->sequence = calloc( module->sequence_len, sizeof( unsigned char ) );
        if( !module->sequence ) {
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->sequence_len; idx++ ) {
            entry = data_u8( data, 80 + idx );
            module->sequence[ idx ] = entry < module->num_patterns ? entry : 0;
        }
        module->patterns = calloc( module->num_patterns, sizeof( struct pattern ) );
        if( !module->patterns ) {
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->num_patterns; idx++ ) {
            if( data_u8( data, offset + 4 ) ) {
                strcpy( message, "Unknown pattern packing type!" );
                dispose_module( module );
                return NULL;
            }
            num_rows = data_u16le( data, offset + 5 );
            if( num_rows < 1 ) {
                num_rows = 1;
            }
            pat_data_len = data_u16le( data, offset + 7 );
            offset += data_u32le( data, offset );
            next_offset = offset + pat_data_len;
            num_notes = num_rows * module->num_channels;
            pattern_data = calloc( num_notes, 5 );
            if( !pattern_data ) {
                dispose_module( module );
                return NULL;
            }
            module->patterns[ idx ].num_channels = module->num_channels;
            module->patterns[ idx ].num_rows = num_rows;
            module->patterns[ idx ].data = pattern_data;
            if( pat_data_len > 0 ) {
                pat_data_offset = 0;
                for( note = 0; note < num_notes; note++ ) {
                    flags = data_u8( data, offset );
                    if( ( flags & 0x80 ) == 0 ) {
                        flags = 0x1F;
                    } else {
                        offset++;
                    }
                    key = ( flags & 0x01 ) > 0 ? data_u8( data, offset++ ) : 0;
                    pattern_data[ pat_data_offset++ ] = key;
                    ins = ( flags & 0x02 ) > 0 ? data_u8( data, offset++ ) : 0;
                    pattern_data[ pat_data_offset++ ] = ins;
                    vol = ( flags & 0x04 ) > 0 ? data_u8( data, offset++ ) : 0;
                    pattern_data[ pat_data_offset++ ] = vol;
                    fxc = ( flags & 0x08 ) > 0 ? data_u8( data, offset++ ) : 0;
                    fxp = ( flags & 0x10 ) > 0 ? data_u8( data, offset++ ) : 0;
                    if( fxc >= 0x40 ) {
                        fxc = fxp = 0;
                    }
                    pattern_data[ pat_data_offset++ ] = fxc;
                    pattern_data[ pat_data_offset++ ] = fxp;
                }
            }
            offset = next_offset;
        }
        module->instruments = calloc( module->num_instruments + 1, sizeof( struct instrument ) );
        if( !module->instruments ) {
            dispose_module( module );
            return NULL;
        }
        instrument = &module->instruments[ 0 ];
        instrument->samples = calloc( 1, sizeof( struct sample ) );
        if( !instrument->samples ) {
            dispose_module( module );
            return NULL;
        }
        for( ins = 1; ins <= module->num_instruments; ins++ ) {
            instrument = &module->instruments[ ins ];
            data_ascii( data, offset + 4, 22, instrument->name );
            num_samples = data_u16le( data, offset + 27 );
            instrument->num_samples = ( num_samples > 0 ) ? num_samples : 1;
            instrument->samples = calloc( instrument->num_samples, sizeof( struct sample ) );
            if( !instrument->samples ) {
                dispose_module( module );
                return NULL;
            }
            if( num_samples > 0 ) {
                for( key = 0; key < 96; key++ ) {
                    instrument->key_to_sample[ key + 1 ] = data_u8( data, offset + 33 + key );
                }
                point_tick = 0;
                for( point = 0; point < 12; point++ ) {
                    point_offset = offset + 129 + ( point * 4 );
                    point_tick = ( delta_env ? point_tick : 0 ) + data_u16le( data, point_offset );
                    instrument->vol_env.points_tick[ point ] = point_tick;
                    instrument->vol_env.points_ampl[ point ] = data_u16le( data, point_offset + 2 );
                }
                point_tick = 0;
                for( point = 0; point < 12; point++ ) {
                    point_offset = offset + 177 + ( point * 4 );
                    point_tick = ( delta_env ? point_tick : 0 ) + data_u16le( data, point_offset );
                    instrument->pan_env.points_tick[ point ] = point_tick;
                    instrument->pan_env.points_ampl[ point ] = data_u16le( data, point_offset + 2 );
                }
                instrument->vol_env.num_points = data_u8( data, offset + 225 );
                if( instrument->vol_env.num_points > 12 ) {
                    instrument->vol_env.num_points = 0;
                }
                instrument->pan_env.num_points = data_u8( data, offset + 226 );
                if( instrument->pan_env.num_points > 12 ) {
                    instrument->pan_env.num_points = 0;
                }
                instrument->vol_env.sustain_tick = instrument->vol_env.points_tick[ data_u8( data, offset + 227 ) & 0xF ];
                instrument->vol_env.loop_start_tick = instrument->vol_env.points_tick[ data_u8( data, offset + 228 ) & 0xF ];
                instrument->vol_env.loop_end_tick = instrument->vol_env.points_tick[ data_u8( data, offset + 229 ) & 0xF ];
                instrument->pan_env.sustain_tick = instrument->pan_env.points_tick[ data_u8( data, offset + 230 ) & 0xF ];
                instrument->pan_env.loop_start_tick = instrument->pan_env.points_tick[ data_u8( data, offset + 231 ) & 0xF ];
                instrument->pan_env.loop_end_tick = instrument->pan_env.points_tick[ data_u8( data, offset + 232 ) & 0xF ];
                instrument->vol_env.enabled = instrument->vol_env.num_points > 0 && ( data_u8( data, offset + 233 ) & 0x1 );
                instrument->vol_env.sustain = ( data_u8( data, offset + 233 ) & 0x2 ) > 0;
                instrument->vol_env.looped = ( data_u8( data, offset + 233 ) & 0x4 ) > 0;
                instrument->pan_env.enabled = instrument->pan_env.num_points > 0 && ( data_u8( data, offset + 234 ) & 0x1 );
                instrument->pan_env.sustain = ( data_u8( data, offset + 234 ) & 0x2 ) > 0;
                instrument->pan_env.looped = ( data_u8( data, offset + 234 ) & 0x4 ) > 0;
                instrument->vib_type = data_u8( data, offset + 235 );
                instrument->vib_sweep = data_u8( data, offset + 236 );
                instrument->vib_depth = data_u8( data, offset + 237 );
                instrument->vib_rate = data_u8( data, offset + 238 );
                instrument->vol_fadeout = data_u16le( data, offset + 239 );
            }
            offset += data_u32le( data, offset );
            sam_head_offset = offset;
            offset += num_samples * 40;
            for( sam = 0; sam < num_samples; sam++ ) {
                sample = &instrument->samples[ sam ];
                sam_data_bytes = data_u32le( data, sam_head_offset );
                sam_loop_start = data_u32le( data, sam_head_offset + 4 );
                sam_loop_length = data_u32le( data, sam_head_offset + 8 );
                sample->volume = data_u8( data, sam_head_offset + 12 );
                sample->fine_tune = data_s8( data, sam_head_offset + 13 );
                looped = ( data_u8( data, sam_head_offset + 14 ) & 0x3 ) > 0;
                ping_pong = ( data_u8( data, sam_head_offset + 14 ) & 0x2 ) > 0;
                sixteen_bit = ( data_u8( data, sam_head_offset + 14 ) & 0x10 ) > 0;
                sample->panning = data_u8( data, sam_head_offset + 15 ) + 1;
                sample->rel_note = data_s8( data, sam_head_offset + 16 );
                data_ascii( data, sam_head_offset + 18, 22, sample->name );
                sam_head_offset += 40;
                sam_data_samples = sam_data_bytes;
                if( sixteen_bit ) {
                    sam_data_samples = sam_data_samples >> 1;
                    sam_loop_start = sam_loop_start >> 1;
                    sam_loop_length = sam_loop_length >> 1;
                }
                if( !looped || ( sam_loop_start + sam_loop_length ) > sam_data_samples ) {
                    sam_loop_start = sam_data_samples;
                    sam_loop_length = 0;
                }
                sample->loop_start = sam_loop_start;
                sample->loop_length = sam_loop_length;
                sample->data = calloc( sam_data_samples + 1, sizeof( short ) );
                if( sample->data ) {
                    if( sixteen_bit ) {
                        data_sam_s16le( data, offset, sam_data_samples, sample->data );
                    } else {
                        data_sam_s8( data, offset, sam_data_samples, sample->data );
                    }
                    amp = 0;
                    for( idx = 0; idx < sam_data_samples; idx++ ) {
                        amp = amp + sample->data[ idx ];
                        amp = ( amp & 0x7FFF ) - ( amp & 0x8000 );
                        sample->data[ idx ] = amp;
                    }
                    sample->data[ sam_loop_start + sam_loop_length ] = sample->data[ sam_loop_start ];
                    if( ping_pong ) {
                        sample_ping_pong( sample );
                    }
                } else {
                    dispose_module( module );
                    return NULL;
                }
                offset += sam_data_bytes;
            }
        }
    }
    return module;
}

static struct module* module_load_s3m( struct data *data, char *message ) {
    int idx, module_data_idx, inst_offset, flags;
    int version, sixteen_bit, tune, signed_samples;
    int stereo_mode, default_pan, channel_map[ 32 ];
    int sample_offset, sample_length, loop_start, loop_length;
    int pat_offset, note_offset, row, chan, token;
    int key, ins, volume, effect, param, panning;
    char *pattern_data;
    struct instrument *instrument;
    struct sample *sample;
    struct module *module = calloc( 1, sizeof( struct module ) );
    if( module ) {
        data_ascii( data, 0, 28, module->name );
        module->sequence_len = data_u16le( data, 32 );
        module->num_instruments = data_u16le( data, 34 );
        module->num_patterns = data_u16le( data, 36 );
        flags = data_u16le( data, 38 );
        version = data_u16le( data, 40 );
        module->fast_vol_slides = ( ( flags & 0x40 ) == 0x40 ) || version == 0x1300;
        signed_samples = data_u16le( data, 42 ) == 1;
        if( data_u32le( data, 44 ) != 0x4d524353 ) {
            strcpy( message, "Not an S3M file!" );
            dispose_module( module );
            return NULL;
        }
        module->default_gvol = data_u8( data, 48 );
        module->default_speed = data_u8( data, 49 );
        module->default_tempo = data_u8( data, 50 );
        module->c2_rate = 8363;
        module->gain = data_u8( data, 51 ) & 0x7F;
        stereo_mode = ( data_u8( data, 51 ) & 0x80 ) == 0x80;
        default_pan = data_u8( data, 53 ) == 0xFC;
        for( idx = 0; idx < 32; idx++ ) {
            channel_map[ idx ] = -1;
            if( data_u8( data, 64 + idx ) < 16 ) {
                channel_map[ idx ] = module->num_channels++;
            }
        }
        module->sequence = calloc( module->sequence_len, sizeof( unsigned char ) );
        if( !module->sequence ){
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->sequence_len; idx++ ) {
            module->sequence[ idx ] = data_u8( data, 96 + idx );
        }
        module_data_idx = 96 + module->sequence_len;
        module->instruments = calloc( module->num_instruments + 1, sizeof( struct instrument ) );
        if( !module->instruments ) {
            dispose_module( module );
            return NULL;
        }
        instrument = &module->instruments[ 0 ];
        instrument->num_samples = 1;
        instrument->samples = calloc( 1, sizeof( struct sample ) );
        if( !instrument->samples ) {
            dispose_module( module );
            return NULL;
        }
        for( ins = 1; ins <= module->num_instruments; ins++ ) {
            instrument = &module->instruments[ ins ];
            instrument->num_samples = 1;
            instrument->samples = calloc( 1, sizeof( struct sample ) );
            if( !instrument->samples ) {
                dispose_module( module );
                return NULL;
            }
            sample = &instrument->samples[ 0 ];
            inst_offset = data_u16le( data, module_data_idx ) << 4;
            module_data_idx += 2;
            data_ascii( data, inst_offset + 48, 28, instrument->name );
            if( data_u8( data, inst_offset ) == 1 && data_u16le( data, inst_offset + 76 ) == 0x4353 ) {
                sample_offset = ( data_u8( data, inst_offset + 13 ) << 20 )
                                + ( data_u16le( data, inst_offset + 14 ) << 4 );
                sample_length = data_u32le( data, inst_offset + 16 );
                loop_start = data_u32le( data, inst_offset + 20 );
                loop_length = data_u32le( data, inst_offset + 24 ) - loop_start;
                sample->volume = data_u8( data, inst_offset + 28 );
                if( data_u8( data, inst_offset + 30 ) != 0 ) {
                    strcpy( message, "Packed samples not supported!" );
                    dispose_module( module );
                    return NULL;
                }
                if( loop_start + loop_length > sample_length ) {
                    loop_length = sample_length - loop_start;
                }
                if( loop_length < 1 || !( data_u8( data, inst_offset + 31 ) & 0x1 ) ) {
                    loop_start = sample_length;
                    loop_length = 0;
                }
                sample->loop_start = loop_start;
                sample->loop_length = loop_length;
                /* stereo = data_u8( data, inst_offset + 31 ) & 0x2; */
                sixteen_bit = data_u8( data, inst_offset + 31 ) & 0x4;
                tune = ( log_2( data_u32le( data, inst_offset + 32 ) ) - log_2( module->c2_rate ) ) * 12;
                sample->rel_note = tune >> FP_SHIFT;
                sample->fine_tune = ( tune & FP_MASK ) >> ( FP_SHIFT - 7 );
                sample->data = calloc( sample_length + 1, sizeof( short ) );
                if( sample->data ) {
                    if( sixteen_bit ) {
                        data_sam_s16le( data, sample_offset, sample_length, sample->data );
                    } else {
                        data_sam_s8( data, sample_offset, sample_length, sample->data );
                    }
                    if( !signed_samples ) {
                        for( idx = 0; idx < sample_length; idx++ ) {
                            sample->data[ idx ] = ( sample->data[ idx ] & 0xFFFF ) - 32768;
                        }
                    }
                    sample->data[ loop_start + loop_length ] = sample->data[ loop_start ];
                } else {
                    dispose_module( module );
                    return NULL;
                }
            }
        }
        module->patterns = calloc( module->num_patterns, sizeof( struct pattern ) );
        if( !module->patterns ) {
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->num_patterns; idx++ ) {
            module->patterns[ idx ].num_channels = module->num_channels;
            module->patterns[ idx ].num_rows = 64;
            pattern_data = calloc( module->num_channels * 64, 5 );
            if( !pattern_data ) {
                dispose_module( module );
                return NULL;
            }
            module->patterns[ idx ].data = pattern_data;
            pat_offset = ( data_u16le( data, module_data_idx ) << 4 ) + 2;
            row = 0;
            while( row < 64 ) {
                token = data_u8( data, pat_offset++ );
                if( token ) {
                    key = ins = 0;
                    if( ( token & 0x20 ) == 0x20 ) {
                        /* Key + Instrument.*/
                        key = data_u8( data, pat_offset++ );
                        ins = data_u8( data, pat_offset++ );
                        if( key < 0xFE ) {
                            key = ( key >> 4 ) * 12 + ( key & 0xF ) + 1;
                        } else if( key == 0xFF ) {
                            key = 0;
                        }
                    }
                    volume = 0;
                    if( ( token & 0x40 ) == 0x40 ) {
                        /* Volume Column.*/
                        volume = ( data_u8( data, pat_offset++ ) & 0x7F ) + 0x10;
                        if( volume > 0x50 ) {
                            volume = 0;
                        }
                    }
                    effect = param = 0;
                    if( ( token & 0x80 ) == 0x80 ) {
                        /* Effect + Param.*/
                        effect = data_u8( data, pat_offset++ );
                        param = data_u8( data, pat_offset++ );
                        if( effect < 1 || effect >= 0x40 ) {
                            effect = param = 0;
                        } else if( effect > 0 ) {
                            effect += 0x80;
                        }
                    }
                    chan = channel_map[ token & 0x1F ];
                    if( chan >= 0 ) {
                        note_offset = ( row * module->num_channels + chan ) * 5;
                        pattern_data[ note_offset     ] = key;
                        pattern_data[ note_offset + 1 ] = ins;
                        pattern_data[ note_offset + 2 ] = volume;
                        pattern_data[ note_offset + 3 ] = effect;
                        pattern_data[ note_offset + 4 ] = param;
                    }
                } else {
                    row++;
                }
            }
            module_data_idx += 2;
        }
        module->default_panning = calloc( module->num_channels, sizeof( unsigned char ) );
        if( module->default_panning ) {
            for( chan = 0; chan < 32; chan++ ) {
                if( channel_map[ chan ] >= 0 ) {
                    panning = 7;
                    if( stereo_mode ) {
                        panning = 12;
                        if( data_u8( data, 64 + chan ) < 8 ) {
                            panning = 3;
                        }
                    }
                    if( default_pan ) {
                        flags = data_u8( data, module_data_idx + chan );
                        if( ( flags & 0x20 ) == 0x20 ) {
                            panning = flags & 0xF;
                        }
                    }
                    module->default_panning[ channel_map[ chan ] ] = panning * 17;
                }
            }
        } else {
            dispose_module( module );
            return NULL;
        }
    }
    return module;
}

static struct module* module_load_mod( struct data *data, char *message ) {
    int idx, pat, module_data_idx, pat_data_len, pat_data_idx;
    int period, key, ins, effect, param, fine_tune;
    int sample_length, loop_start, loop_length;
    char *pattern_data;
    struct instrument *instrument;
    struct sample *sample;
    struct module *module = calloc( 1, sizeof( struct module ) );
    if( module ) {
        data_ascii( data, 0, 20, module->name );
        module->sequence_len = data_u8( data, 950 ) & 0x7F;
        module->restart_pos = data_u8( data, 951 ) & 0x7F;
        if( module->restart_pos >= module->sequence_len ) {
            module->restart_pos = 0;
        }
        module->sequence = calloc( 128, sizeof( unsigned char ) );
        if( !module->sequence ){
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < 128; idx++ ) {
            pat = data_u8( data, 952 + idx ) & 0x7F;
            module->sequence[ idx ] = pat;
            if( pat >= module->num_patterns ) {
                module->num_patterns = pat + 1;
            }
        }
        switch( data_u16be( data, 1082 ) ) {
            case 0x4b2e: /* M.K. */
            case 0x4b21: /* M!K! */
            case 0x5434: /* FLT4 */
                module->num_channels = 4;
                module->c2_rate = 8287;
                module->gain = 64;
                break;
            case 0x484e: /* xCHN */
                module->num_channels = data_u8( data, 1080 ) - 48;
                module->c2_rate = 8363;
                module->gain = 32;
                break;
            case 0x4348: /* xxCH */
                module->num_channels = ( data_u8( data, 1080 ) - 48 ) * 10;
                module->num_channels += data_u8( data, 1081 ) - 48;
                module->c2_rate = 8363;
                module->gain = 32;
                break;
            default:
                strcpy( message, "MOD Format not recognised!" );
                dispose_module( module );
                return NULL;
        }
        module->default_gvol = 64;
        module->default_speed = 6;
        module->default_tempo = 125;
        module->default_panning = calloc( module->num_channels, sizeof( unsigned char ) );
        if( !module->default_panning ) {
            dispose_module( module );
            return NULL;
        }
        for( idx = 0; idx < module->num_channels; idx++ ) {
            module->default_panning[ idx ] = 128 - MOD_STEREO_SEPARATION / 2;
            if( ( idx & 3 ) == 1 || ( idx & 3 ) == 2 ) {
                module->default_panning[ idx ] = 128 + MOD_STEREO_SEPARATION / 2;
            }
        }
        module_data_idx = 1084;
        module->patterns = calloc( module->num_patterns, sizeof( struct pattern ) );
        if( !module->patterns ) {
            dispose_module( module );
            return NULL;
        }
        pat_data_len = module->num_channels * 64 * 5;
        for( pat = 0; pat < module->num_patterns; pat++ ) {
            module->patterns[ pat ].num_channels = module->num_channels;
            module->patterns[ pat ].num_rows = 64;
            pattern_data = calloc( 1, pat_data_len );
            if( !pattern_data ) {
                dispose_module( module );
                return NULL;
            }
            module->patterns[ pat ].data = pattern_data;
            for( pat_data_idx = 0; pat_data_idx < pat_data_len; pat_data_idx += 5 ) {
                period = ( data_u8( data, module_data_idx ) & 0xF ) << 8;
                period = ( period | data_u8( data, module_data_idx + 1 ) ) * 4;
                if( period >= 112 && period <= 6848 ) {
                    key = -12 * log_2( ( period << FP_SHIFT ) / 29021 );
                    key = ( key + ( key & ( FP_ONE >> 1 ) ) ) >> FP_SHIFT;
                    pattern_data[ pat_data_idx ] = key;
                }
                ins = ( data_u8( data, module_data_idx + 2 ) & 0xF0 ) >> 4;
                ins = ins | ( data_u8( data, module_data_idx ) & 0x10 );
                pattern_data[ pat_data_idx + 1 ] = ins;
                effect = data_u8( data, module_data_idx + 2 ) & 0x0F;
                param  = data_u8( data, module_data_idx + 3 );
                if( param == 0 && ( effect < 3 || effect == 0xA ) ) {
                    effect = 0;
                }
                if( param == 0 && ( effect == 5 || effect == 6 ) ) {
                    effect -= 2;
                }
                if( effect == 8 ) {
                    if( module->num_channels == 4 ) {
                        effect = param = 0;
                    } else if( param > 128 ) {
                        param = 128;
                    } else {
                        param = ( param * 255 ) >> 7;
                    }
                }
                pattern_data[ pat_data_idx + 3 ] = effect;
                pattern_data[ pat_data_idx + 4 ] = param;
                module_data_idx += 4;
            }
        }
        module->num_instruments = 31;
        module->instruments = calloc( module->num_instruments + 1, sizeof( struct instrument ) );
        if( !module->instruments ) {
            dispose_module( module );
            return NULL;
        }
        instrument = &module->instruments[ 0 ];
        instrument->num_samples = 1;
        instrument->samples = calloc( 1, sizeof( struct sample ) );
        if( !instrument->samples ) {
            dispose_module( module );
            return NULL;
        }
        for( ins = 1; ins <= module->num_instruments; ins++ ) {
            instrument = &module->instruments[ ins ];
            instrument->num_samples = 1;
            instrument->samples = calloc( 1, sizeof( struct sample ) );
            if( !instrument->samples ) {
                dispose_module( module );
                return NULL;
            }
            sample = &instrument->samples[ 0 ];
            data_ascii( data, ins * 30 - 10, 22, instrument->name );
            sample_length = data_u16be( data, ins * 30 + 12 ) * 2;
            fine_tune = ( data_u8( data, ins * 30 + 14 ) & 0xF ) << 4;
            sample->fine_tune = ( fine_tune & 0x7F ) - ( fine_tune & 0x80 );
            sample->volume = data_u8( data, ins * 30 + 15 ) & 0x7F;
            if( sample->volume > 64 ) {
                sample->volume = 64;
            }
            loop_start = data_u16be( data, ins * 30 + 16 ) * 2;
            loop_length = data_u16be( data, ins * 30 + 18 ) * 2;
            if( loop_start + loop_length > sample_length ) {
                if( loop_start / 2 + loop_length <= sample_length ) {
                    /* Some old modules have loop start in bytes. */
                    loop_start = loop_start / 2;
                } else {
                    loop_length = sample_length - loop_start;
                }
            }
            if( loop_length < 4 ) {
                loop_start = sample_length;
                loop_length = 0;
            }
            sample->loop_start = loop_start;
            sample->loop_length = loop_length;
            sample->data = calloc( sample_length + 1, sizeof( short ) );
            if( sample->data ) {
                data_sam_s8( data, module_data_idx, sample_length, sample->data );
                sample->data[ loop_start + loop_length ] = sample->data[ loop_start ];
            } else {
                dispose_module( module );
                return NULL;
            }
            module_data_idx += sample_length;
        }
    }
    return module;
}

/* Allocate and initialize a module from the specified data, returns NULL on error.
   Message must point to a 64-character buffer to receive error messages. */
struct module* module_load( struct data *data, char *message ) {
    char ascii[ 16 ];
    struct module* module;
    if( !memcmp( data_ascii( data, 0, 16, ascii ), "Extended Module:", 16 ) ) {
        module = module_load_xm( data, message );
    } else if( !memcmp( data_ascii( data, 44, 4, ascii ), "SCRM", 4 ) ) {
        module = module_load_s3m( data, message );
    } else {
        module = module_load_mod( data, message );
    }
    return module;
}

static void pattern_get_note( struct pattern *pattern, int row, int chan, struct note *dest ) {
    int offset = ( row * pattern->num_channels + chan ) * 5;
    if( offset >= 0 && row < pattern->num_rows && chan < pattern->num_channels ) {
        dest->key = pattern->data[ offset ];
        dest->instrument = pattern->data[ offset + 1 ];
        dest->volume = pattern->data[ offset + 2 ];
        dest->effect = pattern->data[ offset + 3 ];
        dest->param = pattern->data[ offset + 4 ];
    } else {
        memset( dest, 0, sizeof( struct note ) );
    }
}

static void channel_init( struct channel *channel, struct replay *replay, int idx ) {
    memset( channel, 0, sizeof( struct channel ) );
    channel->replay = replay;
    channel->id = idx;
    channel->panning = replay->module->default_panning[ idx ];
    channel->instrument = &replay->module->instruments[ 0 ];
    channel->sample = &channel->instrument->samples[ 0 ];
    channel->random_seed = ( idx + 1 ) * 0xABCDEF;
}

static void channel_volume_slide( struct channel *channel ) {
    int up = channel->vol_slide_param >> 4;
    int down = channel->vol_slide_param & 0xF;
    if( down == 0xF && up > 0 ) {
        /* Fine slide up.*/
        if( channel->fx_count == 0 ) {
            channel->volume += up;
        }
    } else if( up == 0xF && down > 0 ) {
        /* Fine slide down.*/
        if( channel->fx_count == 0 ) {
            channel->volume -= down;
        }
    } else if( channel->fx_count > 0 || channel->replay->module->fast_vol_slides ) {
        /* Normal.*/
        channel->volume += up - down;
    }
    if( channel->volume > 64 ) {
        channel->volume = 64;
    }
    if( channel->volume < 0 ) {
        channel->volume = 0;
    }
}

static void channel_porta_up( struct channel *channel, int param ) {
    switch( param & 0xF0 ) {
        case 0xE0: /* Extra-fine porta.*/
            if( channel->fx_count == 0 ) {
                channel->period -= param & 0xF;
            }
            break;
        case 0xF0: /* Fine porta.*/
            if( channel->fx_count == 0 ) {
                channel->period -= ( param & 0xF ) << 2;
            }
            break;
        default:/* Normal porta.*/
            if( channel->fx_count > 0 ) {
                channel->period -= param << 2;
            }
            break;
    }
    if( channel->period < 0 ) {
        channel->period = 0;
    }
}

static void channel_porta_down( struct channel *channel, int param ) {
    if( channel->period > 0 ) {
        switch( param & 0xF0 ) {
            case 0xE0: /* Extra-fine porta.*/
                if( channel->fx_count == 0 ) {
                    channel->period += param & 0xF;
                }
                break;
            case 0xF0: /* Fine porta.*/
                if( channel->fx_count == 0 ) {
                    channel->period += ( param & 0xF ) << 2;
                }
                break;
            default:/* Normal porta.*/
                if( channel->fx_count > 0 ) {
                    channel->period += param << 2;
                }
                break;
        }
        if( channel->period > 65535 ) {
            channel->period = 65535;
        }
    }
}

static void channel_tone_porta( struct channel *channel ) {
    if( channel->period > 0 ) {
        if( channel->period < channel->porta_period ) {
            channel->period += channel->tone_porta_param << 2;
            if( channel->period > channel->porta_period ) {
                channel->period = channel->porta_period;
            }
        } else {
            channel->period -= channel->tone_porta_param << 2;
            if( channel->period < channel->porta_period ) {
                channel->period = channel->porta_period;
            }
        }
    }
}

static int channel_waveform( struct channel *channel, int phase, int type ) {
    int amplitude = 0;
    switch( type ) {
        default: /* Sine. */
            amplitude = sine_table[ phase & 0x1F ];
            if( ( phase & 0x20 ) > 0 ) {
                amplitude = -amplitude;
            }
            break;
        case 6: /* Saw Up.*/
            amplitude = ( ( ( phase + 0x20 ) & 0x3F ) << 3 ) - 255;
            break;
        case 1: case 7: /* Saw Down. */
            amplitude = 255 - ( ( ( phase + 0x20 ) & 0x3F ) << 3 );
            break;
        case 2: case 5: /* Square. */
            amplitude = ( phase & 0x20 ) > 0 ? 255 : -255;
            break;
        case 3: case 8: /* Random. */
            amplitude = ( channel->random_seed >> 20 ) - 255;
            channel->random_seed = ( channel->random_seed * 65 + 17 ) & 0x1FFFFFFF;
            break;
    }
    return amplitude;
}

static void channel_vibrato( struct channel *channel, int fine ) {
    int wave = channel_waveform( channel, channel->vibrato_phase, channel->vibrato_type & 0x3 );
    channel->vibrato_add = wave * channel->vibrato_depth >> ( fine ? 7 : 5 );
}

static void channel_tremolo( struct channel *channel ) {
    int wave = channel_waveform( channel, channel->tremolo_phase, channel->tremolo_type & 0x3 );
    channel->tremolo_add = wave * channel->tremolo_depth >> 6;
}

static void channel_tremor( struct channel *channel ) {
    if( channel->retrig_count >= channel->tremor_on_ticks ) {
        channel->tremolo_add = -64;
    }
    if( channel->retrig_count >= ( channel->tremor_on_ticks + channel->tremor_off_ticks ) ) {
        channel->tremolo_add = channel->retrig_count = 0;
    }
}

static void channel_retrig_vol_slide( struct channel *channel ) {
    if( channel->retrig_count >= channel->retrig_ticks ) {
        channel->retrig_count = channel->sample_idx = channel->sample_fra = 0;
        switch( channel->retrig_volume ) {
            case 0x1: channel->volume = channel->volume -  1; break;
            case 0x2: channel->volume = channel->volume -  2; break;
            case 0x3: channel->volume = channel->volume -  4; break;
            case 0x4: channel->volume = channel->volume -  8; break;
            case 0x5: channel->volume = channel->volume - 16; break;
            case 0x6: channel->volume = channel->volume * 2 / 3; break;
            case 0x7: channel->volume = channel->volume >> 1; break;
            case 0x8: /* ? */ break;
            case 0x9: channel->volume = channel->volume +  1; break;
            case 0xA: channel->volume = channel->volume +  2; break;
            case 0xB: channel->volume = channel->volume +  4; break;
            case 0xC: channel->volume = channel->volume +  8; break;
            case 0xD: channel->volume = channel->volume + 16; break;
            case 0xE: channel->volume = channel->volume * 3 / 2; break;
            case 0xF: channel->volume = channel->volume << 1; break;
        }
        if( channel->volume <  0 ) {
            channel->volume = 0;
        }
        if( channel->volume > 64 ) {
            channel->volume = 64;
        }
    }
}

static void channel_trigger( struct channel *channel ) {
    int key, sam, porta, period, fine_tune, ins = channel->note.instrument;
    struct sample *sample;
    if( ins > 0 && ins <= channel->replay->module->num_instruments ) {
        channel->instrument = &channel->replay->module->instruments[ ins ];
        key = channel->note.key < 97 ? channel->note.key : 0;
        sam = channel->instrument->key_to_sample[ key ];
        sample = &channel->instrument->samples[ sam ];
        channel->volume = sample->volume >= 64 ? 64 : sample->volume & 0x3F;
        if( sample->panning > 0 ) {
            channel->panning = ( sample->panning - 1 ) & 0xFF;
        }
        if( channel->period > 0 && sample->loop_length > 1 ) {
            /* Amiga trigger.*/
            channel->sample = sample;
        }
        channel->sample_off = 0;
        channel->vol_env_tick = channel->pan_env_tick = 0;
        channel->fadeout_vol = 32768;
        channel->key_on = 1;
    }
    if( channel->note.effect == 0x09 || channel->note.effect == 0x8F ) {
        /* Set Sample Offset. */
        if( channel->note.param > 0 ) {
            channel->offset_param = channel->note.param;
        }
        channel->sample_off = channel->offset_param << 8;
    }
    if( channel->note.volume >= 0x10 && channel->note.volume < 0x60 ) {
        channel->volume = channel->note.volume < 0x50 ? channel->note.volume - 0x10 : 64;
    }
    switch( channel->note.volume & 0xF0 ) {
        case 0x80: /* Fine Vol Down.*/
            channel->volume -= channel->note.volume & 0xF;
            if( channel->volume < 0 ) {
                channel->volume = 0;
            }
            break;
        case 0x90: /* Fine Vol Up.*/
            channel->volume += channel->note.volume & 0xF;
            if( channel->volume > 64 ) {
                channel->volume = 64;
            }
            break;
        case 0xA0: /* Set Vibrato Speed.*/
            if( ( channel->note.volume & 0xF ) > 0 ) {
                channel->vibrato_speed = channel->note.volume & 0xF;
            }
            break;
        case 0xB0: /* Vibrato.*/
            if( ( channel->note.volume & 0xF ) > 0 ) {
                channel->vibrato_depth = channel->note.volume & 0xF;
            }
            channel_vibrato( channel, 0 );
            break;
        case 0xC0: /* Set Panning.*/
            channel->panning = ( channel->note.volume & 0xF ) * 17;
            break;
        case 0xF0: /* Tone Porta.*/
            if( ( channel->note.volume & 0xF ) > 0 ) {
                channel->tone_porta_param = channel->note.volume & 0xF;
            }
            break;
    }
    if( channel->note.key > 0 ) {
        if( channel->note.key > 96 ) {
            channel->key_on = 0;
        } else {
            porta = ( channel->note.volume & 0xF0 ) == 0xF0 ||
                    channel->note.effect == 0x03 || channel->note.effect == 0x05 ||
                    channel->note.effect == 0x87 || channel->note.effect == 0x8C;
            if( !porta ) {
                ins = channel->instrument->key_to_sample[ channel->note.key ];
                channel->sample = &channel->instrument->samples[ ins ];
            }
            fine_tune = channel->sample->fine_tune;
            if( channel->note.effect == 0x75 || channel->note.effect == 0xF2 ) {
                /* Set Fine Tune. */
                fine_tune = ( ( channel->note.param & 0xF ) << 4 ) - 128;
            }
            key = channel->note.key + channel->sample->rel_note;
            if( key < 1 ) {
                key = 1;
            }
            if( key > 120 ) {
                key = 120;
            }
            period = ( key << 6 ) + ( fine_tune >> 1 );
            if( channel->replay->module->linear_periods ) {
                channel->porta_period = 7744 - period;
            } else {
                channel->porta_period = 29021 * exp_2( ( period << FP_SHIFT ) / -768 ) >> FP_SHIFT;
            }
            if( !porta ) {
                channel->period = channel->porta_period;
                channel->sample_idx = channel->sample_off;
                channel->sample_fra = 0;
                if( channel->vibrato_type < 4 ) {
                    channel->vibrato_phase = 0;
                }
                if( channel->tremolo_type < 4 ) {
                    channel->tremolo_phase = 0;
                }
                channel->retrig_count = channel->av_count = 0;
            }
        }
    }
}

static void channel_update_envelopes( struct channel *channel ) {
    if( channel->instrument->vol_env.enabled ) {
        if( !channel->key_on ) {
            channel->fadeout_vol -= channel->instrument->vol_fadeout;
            if( channel->fadeout_vol < 0 ) {
                channel->fadeout_vol = 0;
            }
        }
        channel->vol_env_tick = envelope_next_tick( &channel->instrument->vol_env,
                                                    channel->vol_env_tick, channel->key_on );
    }
    if( channel->instrument->pan_env.enabled ) {
        channel->pan_env_tick = envelope_next_tick( &channel->instrument->pan_env,
                                                    channel->pan_env_tick, channel->key_on );
    }
}

static void channel_auto_vibrato( struct channel *channel ) {
    int sweep, rate, type, wave;
    int depth = channel->instrument->vib_depth & 0x7F;
    if( depth > 0 ) {
        sweep = channel->instrument->vib_sweep & 0x7F;
        rate = channel->instrument->vib_rate & 0x7F;
        type = channel->instrument->vib_type;
        if( channel->av_count < sweep ) {
            depth = depth * channel->av_count / sweep;
        }
        wave = channel_waveform( channel, channel->av_count * rate >> 2, type + 4 );
        channel->vibrato_add += wave * depth >> 8;
        channel->av_count++;
    }
}

static void channel_calculate_freq( struct channel *channel ) {
    int per = channel->period + channel->vibrato_add;
    if( channel->replay->module->linear_periods ) {
        per = per - ( channel->arpeggio_add << 6 );
        if( per < 28 || per > 7680 ) {
            per = 7680;
        }
        channel->freq = ( ( channel->replay->module->c2_rate >> 4 )
                          * exp_2( ( ( 4608 - per ) << FP_SHIFT ) / 768 ) ) >> ( FP_SHIFT - 4 );
    } else {
        if( per > 29021 ) {
            per = 29021;
        }
        per = ( per << FP_SHIFT ) / exp_2( ( channel->arpeggio_add << FP_SHIFT ) / 12 );
        if( per < 28 ) {
            per = 29021;
        }
        channel->freq = channel->replay->module->c2_rate * 1712 / per;
    }
}

static void channel_calculate_ampl( struct channel *channel ) {
    int vol, range, env_pan = 32, env_vol = channel->key_on ? 64 : 0;
    if( channel->instrument->vol_env.enabled ) {
        env_vol = envelope_calculate_ampl( &channel->instrument->vol_env, channel->vol_env_tick );
    }
    vol = channel->volume + channel->tremolo_add;
    if( vol > 64 ) {
        vol = 64;
    }
    if( vol < 0 ) {
        vol = 0;
    }
    vol = ( vol * channel->replay->module->gain * FP_ONE ) >> 13;
    vol = ( vol * channel->fadeout_vol ) >> 15;
    channel->ampl = ( vol * channel->replay->global_vol * env_vol ) >> 12;
    if( channel->instrument->pan_env.enabled ) {
        env_pan = envelope_calculate_ampl( &channel->instrument->pan_env, channel->pan_env_tick );
    }
    range = ( channel->panning < 128 ) ? channel->panning : ( 255 - channel->panning );
    channel->pann = channel->panning + ( range * ( env_pan - 32 ) >> 5 );
}

static void channel_tick( struct channel *channel ) {
    channel->vibrato_add = 0;
    channel->fx_count++;
    channel->retrig_count++;
    if( !( channel->note.effect == 0x7D && channel->fx_count <= channel->note.param ) ) {
        switch( channel->note.volume & 0xF0 ) {
            case 0x60: /* Vol Slide Down.*/
                channel->volume -= channel->note.volume & 0xF;
                if( channel->volume < 0 ) {
                    channel->volume = 0;
                }
                break;
            case 0x70: /* Vol Slide Up.*/
                channel->volume += channel->note.volume & 0xF;
                if( channel->volume > 64 ) {
                    channel->volume = 64;
                }
                break;
            case 0xB0: /* Vibrato.*/
                channel->vibrato_phase += channel->vibrato_speed;
                channel_vibrato( channel, 0 );
                break;
            case 0xD0: /* Pan Slide Left.*/
                channel->panning -= channel->note.volume & 0xF;
                if( channel->panning < 0 ) {
                    channel->panning = 0;
                }
                break;
            case 0xE0: /* Pan Slide Right.*/
                channel->panning += channel->note.volume & 0xF;
                if( channel->panning > 255 ) {
                    channel->panning = 255;
                }
                break;
            case 0xF0: /* Tone Porta.*/
                channel_tone_porta( channel );
                break;
        }
    }
    switch( channel->note.effect ) {
        case 0x01: case 0x86: /* Porta Up. */
            channel_porta_up( channel, channel->porta_up_param );
            break;
        case 0x02: case 0x85: /* Porta Down. */
            channel_porta_down( channel, channel->porta_down_param );
            break;
        case 0x03: case 0x87: /* Tone Porta. */
            channel_tone_porta( channel );
            break;
        case 0x04: case 0x88: /* Vibrato. */
            channel->vibrato_phase += channel->vibrato_speed;
            channel_vibrato( channel, 0 );
            break;
        case 0x05: case 0x8C: /* Tone Porta + Vol Slide. */
            channel_tone_porta( channel );
            channel_volume_slide( channel );
            break;
        case 0x06: case 0x8B: /* Vibrato + Vol Slide. */
            channel->vibrato_phase += channel->vibrato_speed;
            channel_vibrato( channel, 0 );
            channel_volume_slide( channel );
            break;
        case 0x07: case 0x92: /* Tremolo. */
            channel->tremolo_phase += channel->tremolo_speed;
            channel_tremolo( channel );
            break;
        case 0x0A: case 0x84: /* Vol Slide. */
            channel_volume_slide( channel );
            break;
        case 0x11: /* Global Volume Slide. */
            channel->replay->global_vol = channel->replay->global_vol
                                          + ( channel->gvol_slide_param >> 4 )
                                          - ( channel->gvol_slide_param & 0xF );
            if( channel->replay->global_vol < 0 ) {
                channel->replay->global_vol = 0;
            }
            if( channel->replay->global_vol > 64 ) {
                channel->replay->global_vol = 64;
            }
            break;
        case 0x19: /* Panning Slide. */
            channel->panning = channel->panning
                               + ( channel->pan_slide_param >> 4 )
                               - ( channel->pan_slide_param & 0xF );
            if( channel->panning < 0 ) {
                channel->panning = 0;
            }
            if( channel->panning > 255 ) {
                channel->panning = 255;
            }
            break;
        case 0x1B: case 0x91: /* Retrig + Vol Slide. */
            channel_retrig_vol_slide( channel );
            break;
        case 0x1D: case 0x89: /* Tremor. */
            channel_tremor( channel );
            break;
        case 0x79: /* Retrig. */
            if( channel->fx_count >= channel->note.param ) {
                channel->fx_count = 0;
                channel->sample_idx = channel->sample_fra = 0;
            }
            break;
        case 0x7C: case 0xFC: /* Note Cut. */
            if( channel->note.param == channel->fx_count ) {
                channel->volume = 0;
            }
            break;
        case 0x7D: case 0xFD: /* Note Delay. */
            if( channel->note.param == channel->fx_count ) {
                channel_trigger( channel );
            }
            break;
        case 0x8A: /* Arpeggio. */
            if( channel->fx_count == 1 ) {
                channel->arpeggio_add = channel->arpeggio_param >> 4;
            } else if( channel->fx_count == 2 ) {
                channel->arpeggio_add = channel->arpeggio_param & 0xF;
            } else {
                channel->arpeggio_add = channel->fx_count = 0;
            }
            break;
        case 0x95: /* Fine Vibrato. */
            channel->vibrato_phase += channel->vibrato_speed;
            channel_vibrato( channel, 1 );
            break;
    }
    channel_auto_vibrato( channel );
    channel_calculate_freq( channel );
    channel_calculate_ampl( channel );
    channel_update_envelopes( channel );
}

static void channel_row( struct channel *channel, struct note *note ) {
    channel->note = *note;
    channel->retrig_count++;
    channel->vibrato_add = channel->tremolo_add = channel->arpeggio_add = channel->fx_count = 0;
    if( !( ( note->effect == 0x7D || note->effect == 0xFD ) && note->param > 0 ) ) {
        /* Not note delay.*/
        channel_trigger( channel );
    }
    switch( channel->note.effect ) {
        case 0x01: case 0x86: /* Porta Up. */
            if( channel->note.param > 0 ) {
                channel->porta_up_param = channel->note.param;
            }
            channel_porta_up( channel, channel->porta_up_param );
            break;
        case 0x02: case 0x85: /* Porta Down. */
            if( channel->note.param > 0 ) {
                channel->porta_down_param = channel->note.param;
            }
            channel_porta_down( channel, channel->porta_down_param );
            break;
        case 0x03: case 0x87: /* Tone Porta. */
            if( channel->note.param > 0 ) {
                channel->tone_porta_param = channel->note.param;
            }
            break;
        case 0x04: case 0x88: /* Vibrato. */
            if( ( channel->note.param >> 4 ) > 0 ) {
                channel->vibrato_speed = channel->note.param >> 4;
            }
            if( ( channel->note.param & 0xF ) > 0 ) {
                channel->vibrato_depth = channel->note.param & 0xF;
            }
            channel_vibrato( channel, 0 );
            break;
        case 0x05: case 0x8C: /* Tone Porta + Vol Slide. */
            if( channel->note.param > 0 ) {
                channel->vol_slide_param = channel->note.param;
            }
            channel_volume_slide( channel );
            break;
        case 0x06: case 0x8B: /* Vibrato + Vol Slide. */
            if( channel->note.param > 0 ) {
                channel->vol_slide_param = channel->note.param;
            }
            channel_vibrato( channel, 0 );
            channel_volume_slide( channel );
            break;
        case 0x07: case 0x92: /* Tremolo. */
            if( ( channel->note.param >> 4 ) > 0 ) {
                channel->tremolo_speed = channel->note.param >> 4;
            }
            if( ( channel->note.param & 0xF ) > 0 ) {
                channel->tremolo_depth = channel->note.param & 0xF;
            }
            channel_tremolo( channel );
            break;
        case 0x08: /* Set Panning.*/
            channel->panning = channel->note.param & 0xFF;
            break;
        case 0x0A: case 0x84: /* Vol Slide. */
            if( channel->note.param > 0 ) {
                channel->vol_slide_param = channel->note.param;
            }
            channel_volume_slide( channel );
            break;
        case 0x0C: /* Set Volume. */
            channel->volume = channel->note.param >= 64 ? 64 : channel->note.param & 0x3F;
            break;
        case 0x10: case 0x96: /* Set Global Volume. */
            channel->replay->global_vol = channel->note.param >= 64 ? 64 : channel->note.param & 0x3F;
            break;
        case 0x11: /* Global Volume Slide. */
            if( channel->note.param > 0 ) {
                channel->gvol_slide_param = channel->note.param;
            }
            break;
        case 0x14: /* Key Off. */
            channel->key_on = 0;
            break;
        case 0x15: /* Set Envelope Tick. */
            channel->vol_env_tick = channel->pan_env_tick = channel->note.param & 0xFF;
            break;
        case 0x19: /* Panning Slide. */
            if( channel->note.param > 0 ) {
                channel->pan_slide_param = channel->note.param;
            }
            break;
        case 0x1B: case 0x91: /* Retrig + Vol Slide. */
            if( ( channel->note.param >> 4 ) > 0 ) {
                channel->retrig_volume = channel->note.param >> 4;
            }
            if( ( channel->note.param & 0xF ) > 0 ) {
                channel->retrig_ticks = channel->note.param & 0xF;
            }
            channel_retrig_vol_slide( channel );
            break;
        case 0x1D: case 0x89: /* Tremor. */
            if( ( channel->note.param >> 4 ) > 0 ) {
                channel->tremor_on_ticks = channel->note.param >> 4;
            }
            if( ( channel->note.param & 0xF ) > 0 ) {
                channel->tremor_off_ticks = channel->note.param & 0xF;
            }
            channel_tremor( channel );
            break;
        case 0x21: /* Extra Fine Porta. */
            if( channel->note.param > 0 ) {
                channel->xfine_porta_param = channel->note.param;
            }
            switch( channel->xfine_porta_param & 0xF0 ) {
                case 0x10:
                    channel_porta_up( channel, 0xE0 | ( channel->xfine_porta_param & 0xF ) );
                    break;
                case 0x20:
                    channel_porta_down( channel, 0xE0 | ( channel->xfine_porta_param & 0xF ) );
                    break;
            }
            break;
        case 0x71: /* Fine Porta Up. */
            if( channel->note.param > 0 ) {
                channel->fine_porta_up_param = channel->note.param;
            }
            channel_porta_up( channel, 0xF0 | ( channel->fine_porta_up_param & 0xF ) );
            break;
        case 0x72: /* Fine Porta Down. */
            if( channel->note.param > 0 ) {
                channel->fine_porta_down_param = channel->note.param;
            }
            channel_porta_down( channel, 0xF0 | ( channel->fine_porta_down_param & 0xF ) );
            break;
        case 0x74: case 0xF3: /* Set Vibrato Waveform. */
            if( channel->note.param < 8 ) {
                channel->vibrato_type = channel->note.param;
            }
            break;
        case 0x77: case 0xF4: /* Set Tremolo Waveform. */
            if( channel->note.param < 8 ) {
                channel->tremolo_type = channel->note.param;
            }
            break;
        case 0x7A: /* Fine Vol Slide Up. */
            if( channel->note.param > 0 ) {
                channel->fine_vslide_up_param = channel->note.param;
            }
            channel->volume += channel->fine_vslide_up_param;
            if( channel->volume > 64 ) {
                channel->volume = 64;
            }
            break;
        case 0x7B: /* Fine Vol Slide Down. */
            if( channel->note.param > 0 ) {
                channel->fine_vslide_down_param = channel->note.param;
            }
            channel->volume -= channel->fine_vslide_down_param;
            if( channel->volume < 0 ) {
                channel->volume = 0;
            }
            break;
        case 0x7C: case 0xFC: /* Note Cut. */
            if( channel->note.param <= 0 ) {
                channel->volume = 0;
            }
            break;
        case 0x8A: /* Arpeggio. */
            if( channel->note.param > 0 ) {
                channel->arpeggio_param = channel->note.param;
            }
            break;
        case 0x95: /* Fine Vibrato.*/
            if( ( channel->note.param >> 4 ) > 0 ) {
                channel->vibrato_speed = channel->note.param >> 4;
            }
            if( ( channel->note.param & 0xF ) > 0 ) {
                channel->vibrato_depth = channel->note.param & 0xF;
            }
            channel_vibrato( channel, 1 );
            break;
        case 0xF8: /* Set Panning. */
            channel->panning = channel->note.param * 17;
            break;
    }
    channel_auto_vibrato( channel );
    channel_calculate_freq( channel );
    channel_calculate_ampl( channel );
    channel_update_envelopes( channel );
}

static void channel_resample( struct channel *channel, int *mix_buf,
                              int offset, int count, int sample_rate, int interpolate ) {
    struct sample *sample = channel->sample;
    int l_gain, r_gain, sam_idx, sam_fra, step;
    int loop_len, loop_end, out_idx, out_end, y, m, c;
    short *sample_data = channel->sample->data;
    if( channel->ampl > 0 ) {
        l_gain = channel->ampl * ( 255 - channel->pann ) >> 8;
        r_gain = channel->ampl * channel->pann >> 8;
        sam_idx = channel->sample_idx;
        sam_fra = channel->sample_fra;
        step = ( channel->freq << ( FP_SHIFT - 3 ) ) / ( sample_rate >> 3 );
        loop_len = sample->loop_length;
        loop_end = sample->loop_start + loop_len;
        out_idx = offset * 2;
        out_end = ( offset + count ) * 2;
        if( interpolate ) {
            while( out_idx < out_end ) {
                if( sam_idx >= loop_end ) {
                    if( loop_len > 1 ) {
                        while( sam_idx >= loop_end ) {
                            sam_idx -= loop_len;
                        }
                    } else {
                        break;
                    }
                }
                c = sample_data[ sam_idx ];
                m = sample_data[ sam_idx + 1 ] - c;
                y = ( ( m * sam_fra ) >> FP_SHIFT ) + c;
                mix_buf[ out_idx++ ] += ( y * l_gain ) >> FP_SHIFT;
                mix_buf[ out_idx++ ] += ( y * r_gain ) >> FP_SHIFT;
                sam_fra += step;
                sam_idx += sam_fra >> FP_SHIFT;
                sam_fra &= FP_MASK;
            }
        } else {
            while( out_idx < out_end ) {
                if( sam_idx >= loop_end ) {
                    if( loop_len > 1 ) {
                        while( sam_idx >= loop_end ) {
                            sam_idx -= loop_len;
                        }
                    } else {
                        break;
                    }
                }
                y = sample_data[ sam_idx ];
                mix_buf[ out_idx++ ] += ( y * l_gain ) >> FP_SHIFT;
                mix_buf[ out_idx++ ] += ( y * r_gain ) >> FP_SHIFT;
                sam_fra += step;
                sam_idx += sam_fra >> FP_SHIFT;
                sam_fra &= FP_MASK;
            }
        }
    }
}

static void channel_update_sample_idx( struct channel *channel, int count, int sample_rate ) {
    struct sample *sample = channel->sample;
    int step = ( channel->freq << ( FP_SHIFT - 3 ) ) / ( sample_rate >> 3 );
    channel->sample_fra += step * count;
    channel->sample_idx += channel->sample_fra >> FP_SHIFT;
    if( channel->sample_idx > sample->loop_start ) {
        if( sample->loop_length > 1 ) {
            channel->sample_idx = sample->loop_start
                                  + ( channel->sample_idx - sample->loop_start ) % sample->loop_length;
        } else {
            channel->sample_idx = sample->loop_start;
        }
    }
    channel->sample_fra &= FP_MASK;
}

static void replay_row( struct replay *replay ) {
    int idx, count;
    struct note note;
    struct pattern *pattern;
    struct channel *channel;
    struct module *module = replay->module;
    if( replay->next_row < 0 ) {
        replay->break_pos = replay->seq_pos + 1;
        replay->next_row = 0;
    }
    if( replay->break_pos >= 0 ) {
        if( replay->break_pos >= module->sequence_len ) {
            replay->break_pos = replay->next_row = 0;
        }
        while( module->sequence[ replay->break_pos ] >= module->num_patterns ) {
            replay->break_pos++;
            if( replay->break_pos >= module->sequence_len ) {
                replay->break_pos = replay->next_row = 0;
            }
        }
        replay->seq_pos = replay->break_pos;
        for( idx = 0; idx < module->num_channels; idx++ ) {
            replay->channels[ idx ].pl_row = 0;
        }
        replay->break_pos = -1;
    }
    pattern = &module->patterns[ module->sequence[ replay->seq_pos ] ];
    replay->row = replay->next_row;
    if( replay->row >= pattern->num_rows ) {
        replay->row = 0;
    }
    if( replay->play_count && replay->play_count[ 0 ] ) {
        count = replay->play_count[ replay->seq_pos ][ replay->row ];
        if( replay->pl_count < 0 && count < 127 ) {
            replay->play_count[ replay->seq_pos ][ replay->row ] = count + 1;
        }
    }
    replay->next_row = replay->row + 1;
    if( replay->next_row >= pattern->num_rows ) {
        replay->next_row = -1;
    }
    for( idx = 0; idx < module->num_channels; idx++ ) {
        channel = &replay->channels[ idx ];
        pattern_get_note( pattern, replay->row, idx, &note );
        if( note.effect == 0xE ) {
            note.effect = 0x70 | ( note.param >> 4 );
            note.param &= 0xF;
        }
        if( note.effect == 0x93 ) {
            note.effect = 0xF0 | ( note.param >> 4 );
            note.param &= 0xF;
        }
        if( note.effect == 0 && note.param > 0 ) {
            note.effect = 0x8A;
        }
        channel_row( channel, &note );
        switch( note.effect ) {
            case 0x81: /* Set Speed. */
                if( note.param > 0 ) {
                    replay->tick = replay->speed = note.param;
                }
                break;
            case 0xB: case 0x82: /* Pattern Jump.*/
                if( replay->pl_count < 0 ) {
                    replay->break_pos = note.param;
                    replay->next_row = 0;
                }
                break;
            case 0xD: case 0x83: /* Pattern Break.*/
                if( replay->pl_count < 0 ) {
                    if( replay->break_pos < 0 ) {
                        replay->break_pos = replay->seq_pos + 1;
                    }
                    replay->next_row = ( note.param >> 4 ) * 10 + ( note.param & 0xF );
                }
                break;
            case 0xF: /* Set Speed/Tempo.*/
                if( note.param > 0 ) {
                    if( note.param < 32 ) {
                        replay->tick = replay->speed = note.param;
                    } else {
                        replay->tempo = note.param;
                    }
                }
                break;
            case 0x94: /* Set Tempo.*/
                if( note.param > 32 ) {
                    replay->tempo = note.param;
                }
                break;
            case 0x76: case 0xFB : /* Pattern Loop.*/
                if( note.param == 0 ) {
                    /* Set loop marker on this channel. */
                    channel->pl_row = replay->row;
                }
                if( channel->pl_row < replay->row && replay->break_pos < 0 ) {
                    /* Marker valid. */
                    if( replay->pl_count < 0 ) {
                        /* Not already looping, begin. */
                        replay->pl_count = note.param;
                        replay->pl_chan = idx;
                    }
                    if( replay->pl_chan == idx ) {
                        /* Next Loop.*/
                        if( replay->pl_count == 0 ) {
                            /* Loop finished. Invalidate current marker. */
                            channel->pl_row = replay->row + 1;
                        } else {
                            /* Loop. */
                            replay->next_row = channel->pl_row;
                        }
                        replay->pl_count--;
                    }
                }
                break;
            case 0x7E: case 0xFE: /* Pattern Delay.*/
                replay->tick = replay->speed + replay->speed * note.param;
                break;
        }
    }
}

static int replay_tick( struct replay *replay ) {
    int idx, num_channels, count = 1;
    if( --replay->tick <= 0 ) {
        replay->tick = replay->speed;
        replay_row( replay );
    } else {
        num_channels = replay->module->num_channels;
        for( idx = 0; idx < num_channels; idx++ ) {
            channel_tick( &replay->channels[ idx ] );
        }
    }
    if( replay->play_count && replay->play_count[ 0 ] ) {
        count = replay->play_count[ replay->seq_pos ][ replay->row ] - 1;
    }
    return count;
}

static int module_init_play_count( struct module *module, char **play_count ) {
    int idx, pat, rows, len = 0;
    for( idx = 0; idx < module->sequence_len; idx++ ) {
        pat = module->sequence[ idx ];
        rows = ( pat < module->num_patterns ) ? module->patterns[ pat ].num_rows : 0;
        if( play_count ) {
            play_count[ idx ] = play_count[ 0 ] ? &play_count[ 0 ][ len ] : NULL;
        }
        len += rows;
    }
    return len;
}

/* Set the pattern in the sequence to play. The tempo is reset to the default. */
void replay_set_sequence_pos( struct replay *replay, int pos ) {
    int idx;
    struct module *module = replay->module;
    if( pos >= module->sequence_len ) {
        pos = 0;
    }
    replay->break_pos = pos;
    replay->next_row = 0;
    replay->tick = 1;
    replay->global_vol = module->default_gvol;
    replay->speed = module->default_speed > 0 ? module->default_speed : 6;
    replay->tempo = module->default_tempo > 0 ? module->default_tempo : 125;
    replay->pl_count = replay->pl_chan = -1;
    if( replay->play_count ) {
        free( replay->play_count[ 0 ] );
        free( replay->play_count );
    }
    replay->play_count = calloc( module->sequence_len, sizeof( char * ) );
    if( replay->play_count ) {
        replay->play_count[ 0 ] = calloc( module_init_play_count( module, NULL ), sizeof( char ) );
        module_init_play_count( module, replay->play_count );
    }
    for( idx = 0; idx < module->num_channels; idx++ ) {
        channel_init( &replay->channels[ idx ], replay, idx );
    }
    memset( replay->ramp_buf, 0, 128 * sizeof( int ) );
    replay_tick( replay );
}

/* Deallocate the specified replay. */
void dispose_replay( struct replay *replay ) {
    if( replay->play_count ) {
        free( replay->play_count[ 0 ] );
        free( replay->play_count );
    }
    free( replay->ramp_buf );
    free( replay->channels );
    free( replay );
}

/* Allocate and initialize a replay with the specified sampling rate and interpolation. */
struct replay* new_replay( struct module *module, int sample_rate, int interpolation ) {
    struct replay *replay = calloc( 1, sizeof( struct replay ) );
    if( replay ) {
        replay->module = module;
        replay->sample_rate = sample_rate;
        replay->interpolation = interpolation;
        replay->ramp_buf = calloc( 128, sizeof( int ) );
        replay->channels = calloc( module->num_channels, sizeof( struct channel ) );
        if( replay->ramp_buf && replay->channels ) {
            replay_set_sequence_pos( replay, 0 );
        } else {
            dispose_replay( replay );
            replay = NULL;
        }
    }
    return replay;
}

static int calculate_tick_len( int tempo, int sample_rate, int speed_percent ) {
    return 100 * ( sample_rate * 5 ) / ( tempo * 2 ) / speed_percent;
}

/* Returns the length of the output buffer required by replay_get_audio(). */
int calculate_mix_buf_len( int sample_rate, int speed_percent ) {
    return ( calculate_tick_len( 32, sample_rate, speed_percent ) + 65 ) * 4;
}

/* Returns the song duration in samples at the current sampling rate. */
int replay_calculate_duration( struct replay *replay, int speed_multiplier_percent ) {
    int count = 0, duration = 0;
    replay_set_sequence_pos( replay, 0 );
    while( count < 1 ) {
        duration += calculate_tick_len( replay->tempo, replay->sample_rate, speed_multiplier_percent );
        count = replay_tick( replay );
    }
    replay_set_sequence_pos( replay, 0 );
    return duration;
}

/* Seek to approximately the specified sample position.
   The actual sample position reached is returned. */
/*
int replay_seek( struct replay *replay, int sample_pos ) {
    int idx, tick_len, current_pos = 0;
    replay_set_sequence_pos( replay, 0 );
    tick_len = calculate_tick_len( replay->tempo, replay->sample_rate );
    while( ( sample_pos - current_pos ) >= tick_len ) {
        for( idx = 0; idx < replay->module->num_channels; idx++ ) {
            channel_update_sample_idx( &replay->channels[ idx ],
                                       tick_len * 2, replay->sample_rate * 2 );
        }
        current_pos += tick_len;
        replay_tick( replay );
        tick_len = calculate_tick_len( replay->tempo, replay->sample_rate );
    }
    return current_pos;
}
 */

static void replay_volume_ramp( struct replay *replay, int *mix_buf, int tick_len ) {
    int idx, a1, a2, ramp_rate = 256 * 2048 / replay->sample_rate;
    for( idx = 0, a1 = 0; a1 < 256; idx += 2, a1 += ramp_rate ) {
        a2 = 256 - a1;
        mix_buf[ idx     ] = ( mix_buf[ idx     ] * a1 + replay->ramp_buf[ idx     ] * a2 ) >> 8;
        mix_buf[ idx + 1 ] = ( mix_buf[ idx + 1 ] * a1 + replay->ramp_buf[ idx + 1 ] * a2 ) >> 8;
    }
    memcpy( replay->ramp_buf, &mix_buf[ tick_len * 2 ], 128 * sizeof( int ) );
}

/* 2:1 downsampling with simple but effective anti-aliasing. Buf must contain count * 2 + 1 stereo samples. */
static void downsample( int *buf, int count ) {
    int idx, out_idx, out_len = count * 2;
    for( idx = 0, out_idx = 0; out_idx < out_len; idx += 4, out_idx += 2 ) {
        buf[ out_idx     ] = ( buf[ idx     ] >> 2 ) + ( buf[ idx + 2 ] >> 1 ) + ( buf[ idx + 4 ] >> 2 );
        buf[ out_idx + 1 ] = ( buf[ idx + 1 ] >> 2 ) + ( buf[ idx + 3 ] >> 1 ) + ( buf[ idx + 5 ] >> 2 );
    }
}

/* Generates audio and returns the number of stereo samples written into mix_buf.
   Individual channels may be excluded using the mute bitmask. */
int replay_get_audio( struct replay *replay, int *mix_buf, int mute, int speed_multiplier ) {
    struct channel *channel;
    int idx, num_channels, tick_len = calculate_tick_len( replay->tempo, replay->sample_rate, speed_multiplier );
    /* Clear output buffer. */
    memset( mix_buf, 0, ( tick_len + 65 ) * 4 * sizeof( int ) );
    /* Resample. */
    num_channels = replay->module->num_channels;
    for( idx = 0; idx < num_channels; idx++ ) {
        channel = &replay->channels[ idx ];
        if( !( mute & 1 ) ) {
            channel_resample( channel, mix_buf, 0, ( tick_len + 65 ) * 2,
                              replay->sample_rate * 2, replay->interpolation );
        }
        channel_update_sample_idx( channel, tick_len * 2, replay->sample_rate * 2 );
        mute >>= 1;
    }
    downsample( mix_buf, tick_len + 64 );
    replay_volume_ramp( replay, mix_buf, tick_len );
    replay_tick( replay );
    return tick_len;
}

/* Returns the currently playing pattern in the sequence.*/
int replay_get_sequence_pos( struct replay *replay ) {
    return replay->seq_pos;
}

/* Returns the currently playing row in the pattern. */
int replay_get_row( struct replay *replay ) {
    return replay->row;
}