ref: 20c032d27c59d65b19b8ffbb2608e5282fe817eb
dir: /silk/LPC_analysis_filter.c/
/***********************************************************************
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***********************************************************************/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
#include "celt_lpc.h"
/*******************************************/
/* LPC analysis filter */
/* NB! State is kept internally and the */
/* filter always starts with zero state */
/* first d output samples are set to zero */
/*******************************************/
/* OPT: Using celt_fir() for this function should be faster, but it may cause
integer overflows in intermediate values (not final results), which the
current implementation silences by casting to unsigned. Enabling
this should be safe in pretty much all cases, even though it is not technically
C89-compliant. */
#define USE_CELT_FIR 0
void silk_LPC_analysis_filter(
opus_int16 *out, /* O Output signal */
const opus_int16 *in, /* I Input signal */
const opus_int16 *B, /* I MA prediction coefficients, Q12 [order] */
const opus_int32 len, /* I Signal length */
const opus_int32 d, /* I Filter order */
int arch /* I Run-time architecture */
)
{
opus_int j;
#if defined(FIXED_POINT) && USE_CELT_FIR
opus_int16 num[SILK_MAX_ORDER_LPC];
#else
int ix;
opus_int32 out32_Q12, out32;
const opus_int16 *in_ptr;
#endif
celt_assert( d >= 6 );
celt_assert( (d & 1) == 0 );
celt_assert( d <= len );
#if defined(FIXED_POINT) && USE_CELT_FIR
celt_assert( d <= SILK_MAX_ORDER_LPC );
for ( j = 0; j < d; j++ ) {
num[ j ] = -B[ j ];
}
celt_fir( in + d, num, out + d, len - d, d, arch );
for ( j = 0; j < d; j++ ) {
out[ j ] = 0;
}
#else
(void)arch;
for( ix = d; ix < len; ix++ ) {
in_ptr = &in[ ix - 1 ];
out32_Q12 = silk_SMULBB( in_ptr[ 0 ], B[ 0 ] );
/* Allowing wrap around so that two wraps can cancel each other. The rare
cases where the result wraps around can only be triggered by invalid streams*/
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -1 ], B[ 1 ] );
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -2 ], B[ 2 ] );
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -3 ], B[ 3 ] );
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -4 ], B[ 4 ] );
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -5 ], B[ 5 ] );
for( j = 6; j < d; j += 2 ) {
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -j ], B[ j ] );
out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -j - 1 ], B[ j + 1 ] );
}
/* Subtract prediction */
out32_Q12 = silk_SUB32_ovflw( silk_LSHIFT( (opus_int32)in_ptr[ 1 ], 12 ), out32_Q12 );
/* Scale to Q0 */
out32 = silk_RSHIFT_ROUND( out32_Q12, 12 );
/* Saturate output */
out[ ix ] = (opus_int16)silk_SAT16( out32 );
}
/* Set first d output samples to zero */
silk_memset( out, 0, d * sizeof( opus_int16 ) );
#endif
}