ref: a1330dd9e6d91aa52faa914a9f38eb5790edde8a
dir: /libgsm/lpc.c/
/*
* Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
* Universitaet Berlin. See the accompanying file "COPYRIGHT" for
* details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
*/
/* $Header: /cvsroot/sox/sox/libgsm/lpc.c,v 1.2 2007/11/04 16:32:36 robs Exp $ */
#include <stdio.h>
#include <assert.h>
#include "private.h"
#include "gsm.h"
/*
* 4.2.4 .. 4.2.7 LPC ANALYSIS SECTION
*/
/* 4.2.4 */
static void Autocorrelation (
word * s, /* [0..159] IN/OUT */
longword * L_ACF) /* [0..8] OUT */
/*
* The goal is to compute the array L_ACF[k]. The signal s[i] must
* be scaled in order to avoid an overflow situation.
*/
{
register int k, i;
word temp, smax, scalauto;
#ifdef USE_FLOAT_MUL
float float_s[160];
#endif
/* Dynamic scaling of the array s[0..159]
*/
/* Search for the maximum.
*/
smax = 0;
for (k = 0; k <= 159; k++) {
temp = GSM_ABS( s[k] );
if (temp > smax) smax = temp;
}
/* Computation of the scaling factor.
*/
if (smax == 0) scalauto = 0;
else {
assert(smax > 0);
scalauto = 4 - gsm_norm( (longword)smax << 16 );/* sub(4,..) */
}
/* Scaling of the array s[0...159]
*/
if (scalauto > 0) {
# ifdef USE_FLOAT_MUL
# define SCALE(n) \
case n: for (k = 0; k <= 159; k++) \
float_s[k] = (float) \
(s[k] = GSM_MULT_R(s[k], 16384 >> (n-1)));\
break;
# else
# define SCALE(n) \
case n: for (k = 0; k <= 159; k++) \
s[k] = GSM_MULT_R( s[k], 16384 >> (n-1) );\
break;
# endif /* USE_FLOAT_MUL */
switch (scalauto) {
SCALE(1)
SCALE(2)
SCALE(3)
SCALE(4)
}
# undef SCALE
}
# ifdef USE_FLOAT_MUL
else for (k = 0; k <= 159; k++) float_s[k] = (float) s[k];
# endif
/* Compute the L_ACF[..].
*/
{
# ifdef USE_FLOAT_MUL
register float * sp = float_s;
register float sl = *sp;
# define STEP(k) L_ACF[k] += (longword)(sl * sp[ -(k) ]);
# else
word * sp = s;
word sl = *sp;
# define STEP(k) L_ACF[k] += ((longword)sl * sp[ -(k) ]);
# endif
# define NEXTI sl = *++sp
for (k = 9; k--; L_ACF[k] = 0) ;
STEP (0);
NEXTI;
STEP(0); STEP(1);
NEXTI;
STEP(0); STEP(1); STEP(2);
NEXTI;
STEP(0); STEP(1); STEP(2); STEP(3);
NEXTI;
STEP(0); STEP(1); STEP(2); STEP(3); STEP(4);
NEXTI;
STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5);
NEXTI;
STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6);
NEXTI;
STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); STEP(7);
for (i = 8; i <= 159; i++) {
NEXTI;
STEP(0);
STEP(1); STEP(2); STEP(3); STEP(4);
STEP(5); STEP(6); STEP(7); STEP(8);
}
for (k = 9; k--; L_ACF[k] <<= 1) ;
}
/* Rescaling of the array s[0..159]
*/
if (scalauto > 0) {
assert(scalauto <= 4);
for (k = 160; k--; *s++ <<= scalauto) ;
}
}
#if defined(USE_FLOAT_MUL) && defined(FAST)
static void Fast_Autocorrelation (
word * s, /* [0..159] IN/OUT */
longword * L_ACF) /* [0..8] OUT */
{
register int k, i;
float f_L_ACF[9];
float scale;
float s_f[160];
register float *sf = s_f;
for (i = 0; i < 160; ++i) sf[i] = s[i];
for (k = 0; k <= 8; k++) {
register float L_temp2 = 0;
register float *sfl = sf - k;
for (i = k; i < 160; ++i) L_temp2 += sf[i] * sfl[i];
f_L_ACF[k] = L_temp2;
}
scale = MAX_LONGWORD / f_L_ACF[0];
for (k = 0; k <= 8; k++) {
L_ACF[k] = f_L_ACF[k] * scale;
}
}
#endif /* defined (USE_FLOAT_MUL) && defined (FAST) */
/* 4.2.5 */
static void Reflection_coefficients (
longword * L_ACF, /* 0...8 IN */
register word * r /* 0...7 OUT */
)
{
register int i, m, n;
register word temp;
register longword ltmp;
word ACF[9]; /* 0..8 */
word P[ 9]; /* 0..8 */
word K[ 9]; /* 2..8 */
/* Schur recursion with 16 bits arithmetic.
*/
if (L_ACF[0] == 0) {
for (i = 8; i--; *r++ = 0) ;
return;
}
assert( L_ACF[0] != 0 );
temp = gsm_norm( L_ACF[0] );
assert(temp >= 0 && temp < 32);
/* ? overflow ? */
for (i = 0; i <= 8; i++) ACF[i] = SASR( L_ACF[i] << temp, 16 );
/* Initialize array P[..] and K[..] for the recursion.
*/
for (i = 1; i <= 7; i++) K[ i ] = ACF[ i ];
for (i = 0; i <= 8; i++) P[ i ] = ACF[ i ];
/* Compute reflection coefficients
*/
for (n = 1; n <= 8; n++, r++) {
temp = P[1];
temp = GSM_ABS(temp);
if (P[0] < temp) {
for (i = n; i <= 8; i++) *r++ = 0;
return;
}
*r = gsm_div( temp, P[0] );
assert(*r >= 0);
if (P[1] > 0) *r = -*r; /* r[n] = sub(0, r[n]) */
assert (*r != MIN_WORD);
if (n == 8) return;
/* Schur recursion
*/
temp = GSM_MULT_R( P[1], *r );
P[0] = GSM_ADD( P[0], temp );
for (m = 1; m <= 8 - n; m++) {
temp = GSM_MULT_R( K[ m ], *r );
P[m] = GSM_ADD( P[ m+1 ], temp );
temp = GSM_MULT_R( P[ m+1 ], *r );
K[m] = GSM_ADD( K[ m ], temp );
}
}
}
/* 4.2.6 */
static void Transformation_to_Log_Area_Ratios (
register word * r /* 0..7 IN/OUT */
)
/*
* The following scaling for r[..] and LAR[..] has been used:
*
* r[..] = integer( real_r[..]*32768. ); -1 <= real_r < 1.
* LAR[..] = integer( real_LAR[..] * 16384 );
* with -1.625 <= real_LAR <= 1.625
*/
{
register word temp;
register int i;
/* Computation of the LAR[0..7] from the r[0..7]
*/
for (i = 1; i <= 8; i++, r++) {
temp = *r;
temp = GSM_ABS(temp);
assert(temp >= 0);
if (temp < 22118) {
temp >>= 1;
} else if (temp < 31130) {
assert( temp >= 11059 );
temp -= 11059;
} else {
assert( temp >= 26112 );
temp -= 26112;
temp <<= 2;
}
*r = *r < 0 ? -temp : temp;
assert( *r != MIN_WORD );
}
}
/* 4.2.7 */
static void Quantization_and_coding (
register word * LAR /* [0..7] IN/OUT */
)
{
register word temp;
longword ltmp;
/* This procedure needs four tables; the following equations
* give the optimum scaling for the constants:
*
* A[0..7] = integer( real_A[0..7] * 1024 )
* B[0..7] = integer( real_B[0..7] * 512 )
* MAC[0..7] = maximum of the LARc[0..7]
* MIC[0..7] = minimum of the LARc[0..7]
*/
# undef STEP
# define STEP( A, B, MAC, MIC ) \
temp = GSM_MULT( A, *LAR ); \
temp = GSM_ADD( temp, B ); \
temp = GSM_ADD( temp, 256 ); \
temp = SASR( temp, 9 ); \
*LAR = temp>MAC ? MAC - MIC : (temp<MIC ? 0 : temp - MIC); \
LAR++;
STEP( 20480, 0, 31, -32 );
STEP( 20480, 0, 31, -32 );
STEP( 20480, 2048, 15, -16 );
STEP( 20480, -2560, 15, -16 );
STEP( 13964, 94, 7, -8 );
STEP( 15360, -1792, 7, -8 );
STEP( 8534, -341, 3, -4 );
STEP( 9036, -1144, 3, -4 );
# undef STEP
}
void Gsm_LPC_Analysis (
struct gsm_state *S,
word * s, /* 0..159 signals IN/OUT */
word * LARc) /* 0..7 LARc's OUT */
{
longword L_ACF[9];
(void)S; /* Denotes intentionally unused */
#if defined(USE_FLOAT_MUL) && defined(FAST)
if (S->fast) Fast_Autocorrelation (s, L_ACF );
else
#endif
Autocorrelation (s, L_ACF );
Reflection_coefficients (L_ACF, LARc );
Transformation_to_Log_Area_Ratios (LARc);
Quantization_and_coding (LARc);
}