ref: 3c8b42f039405f6938faaa32234292b55e1b8eea
dir: /src/mask.c/
/*
* July 5, 1991
* Copyright 1991 Lance Norskog And Sundry Contributors
* This source code is freely redistributable and may be used for
* any purpose. This copyright notice must be maintained.
* Lance Norskog And Sundry Contributors are not responsible for
* the consequences of using this software.
*/
/*
* Sound Tools masking noise effect file.
*/
#include <stdlib.h>
#include <math.h>
#include "st_i.h"
static st_effect_t st_mask_effect;
#define HALFABIT 1.44 /* square root of 2 */
/*
* Problems:
* 1) doesn't allow specification of noise depth
* 2) does triangular noise, could do local shaping
* 3) can run over 32 bits.
*/
/*
* Process options
*/
static int st_mask_getopts(eff_t effp UNUSED, int n, char **argv UNUSED)
{
if (n)
{
st_fail(st_mask_effect.usage);
return (ST_EOF);
}
/* should take # of bits */
st_initrand();
return (ST_SUCCESS);
}
/*
* Processed signed long samples from ibuf to obuf.
* Return number of samples processed.
*/
static int st_mask_flow(eff_t effp, const st_sample_t *ibuf, st_sample_t *obuf,
st_size_t *isamp, st_size_t *osamp)
{
int len, done;
st_sample_t l;
st_sample_t tri16; /* 16 signed bits of triangular noise */
len = ((*isamp > *osamp) ? *osamp : *isamp);
switch (effp->outinfo.encoding) {
case ST_ENCODING_ULAW:
case ST_ENCODING_ALAW:
for(done = 0; done < len; done++) {
tri16 =
((rand()%32768L) + (rand()%32768L)) - 32767;
l = *ibuf++ + tri16*16*HALFABIT; /* 2^4.5 */
*obuf++ = l;
}
break;
default:
switch (effp->outinfo.size) {
case ST_SIZE_BYTE:
for(done = 0; done < len; done++) {
tri16 =
((rand()%32768L) + (rand()%32768L)) - 32767;
l = *ibuf++ + tri16*256*HALFABIT; /* 2^8.5 */
*obuf++ = l;
}
break;
case ST_SIZE_WORD:
for(done = 0; done < len; done++) {
tri16 =
((rand()%32768L) + (rand()%32768L)) - 32767;
l = *ibuf++ + tri16*HALFABIT; /* 2^.5 */
*obuf++ = l;
}
break;
default: /* Mask (dither) not needed at >= 24 bits */
for(done = 0; done < len; done++) {
*obuf++ = *ibuf++;
}
break;
}
}
*isamp = done;
*osamp = done;
return (ST_SUCCESS);
}
static st_effect_t st_mask_effect = {
"mask",
"Usage: Mask effect takes no options",
ST_EFF_MCHAN,
st_mask_getopts,
st_effect_nothing,
st_mask_flow,
st_effect_nothing_drain,
st_effect_nothing
};
const st_effect_t *st_mask_effect_fn(void)
{
return &st_mask_effect;
}