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/* libFLAC - Free Lossless Audio Codec library
* Copyright (C) 2000,2001 Josh Coalson
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include "FLAC/format.h"
#include "private/lpc.h"
#ifndef M_LN2
/* math.h in VC++ doesn't seem to have this (how Microsoft is that?) */
#define M_LN2 0.69314718055994530942
#endif
#define LOCAL_FABS(x) ((x)<0.0? -(x):(x))
void FLAC__lpc_compute_autocorrelation(const real data[], unsigned data_len, unsigned lag, real autoc[])
{
/* a readable, but slower, version */
#if 0
real d;
unsigned i;
assert(lag > 0);
assert(lag <= data_len);
while(lag--) {
for(i = lag, d = 0.0; i < data_len; i++)
d += data[i] * data[i - lag];
autoc[lag] = d;
}
#endif
/*
* this version tends to run faster because of better data locality
* ('data_len' is usually much larger than 'lag')
*/
real d;
unsigned sample, coeff;
const unsigned limit = data_len - lag;
assert(lag > 0);
assert(lag <= data_len);
for(coeff = 0; coeff < lag; coeff++)
autoc[coeff] = 0.0;
for(sample = 0; sample <= limit; sample++) {
d = data[sample];
for(coeff = 0; coeff < lag; coeff++)
autoc[coeff] += d * data[sample+coeff];
}
for(; sample < data_len; sample++) {
d = data[sample];
for(coeff = 0; coeff < data_len - sample; coeff++)
autoc[coeff] += d * data[sample+coeff];
}
}
void FLAC__lpc_compute_lp_coefficients(const real autoc[], unsigned max_order, real lp_coeff[][FLAC__MAX_LPC_ORDER], real error[])
{
unsigned i, j;
real r, err, ref[FLAC__MAX_LPC_ORDER], lpc[FLAC__MAX_LPC_ORDER];
assert(0 < max_order);
assert(max_order <= FLAC__MAX_LPC_ORDER);
assert(autoc[0] != 0.0);
err = autoc[0];
for(i = 0; i < max_order; i++) {
/* Sum up this iteration's reflection coefficient. */
r = -autoc[i+1];
for(j = 0; j < i; j++)
r -= lpc[j] * autoc[i-j];
ref[i] = (r/=err);
/* Update LPC coefficients and total error. */
lpc[i]=r;
for(j = 0; j < (i>>1); j++) {
real tmp = lpc[j];
lpc[j] += r * lpc[i-1-j];
lpc[i-1-j] += r * tmp;
}
if(i & 1)
lpc[j] += lpc[j] * r;
err *= (1.0 - r * r);
/* save this order */
for(j = 0; j <= i; j++)
lp_coeff[i][j] = -lpc[j]; /* negate FIR filter coeff to get predictor coeff */
error[i] = err;
}
}
int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsigned precision, unsigned bits_per_sample, int32 qlp_coeff[], int *shift)
{
unsigned i;
real d, cmax = -1e10;
assert(bits_per_sample > 0);
assert(bits_per_sample <= sizeof(int32)*8);
assert(precision > 0);
assert(precision >= FLAC__MIN_QLP_COEFF_PRECISION);
assert(precision + bits_per_sample < sizeof(int32)*8);
#ifdef NDEBUG
(void)bits_per_sample; /* silence compiler warning about unused parameter */
#endif
/* drop one bit for the sign; from here on out we consider only |lp_coeff[i]| */
precision--;
for(i = 0; i < order; i++) {
if(lp_coeff[i] == 0.0)
continue;
d = LOCAL_FABS(lp_coeff[i]);
if(d > cmax)
cmax = d;
}
if(cmax < 0.0) {
/* => coefficients are all 0, which means our constant-detect didn't work */
return 2;
}
else {
const int maxshift = (int)precision - (int)floor(log(cmax) / M_LN2) - 1;
const int max_shiftlimit = (1 << (FLAC__SUBFRAME_LPC_QLP_SHIFT_LEN-1)) - 1;
const int min_shiftlimit = -max_shiftlimit - 1;
*shift = maxshift;
if(*shift < min_shiftlimit || *shift > max_shiftlimit) {
return 1;
}
}
if(*shift != 0) { /* just to avoid wasting time... */
for(i = 0; i < order; i++)
qlp_coeff[i] = (int32)floor(lp_coeff[i] * (real)(1 << *shift));
}
return 0;
}
void FLAC__lpc_compute_residual_from_qlp_coefficients(const int32 data[], unsigned data_len, const int32 qlp_coeff[], unsigned order, int lp_quantization, int32 residual[])
{
#ifdef FLAC__OVERFLOW_DETECT
int64 sumo;
#endif
unsigned i, j;
int32 sum;
const int32 *history;
#ifdef FLAC__OVERFLOW_DETECT_VERBOSE
fprintf(stderr,"FLAC__lpc_compute_residual_from_qlp_coefficients: data_len=%d, order=%u, lpq=%d",data_len,order,lp_quantization);
for(i=0;i<order;i++)
fprintf(stderr,", q[%u]=%d",i,qlp_coeff[i]);
fprintf(stderr,"\n");
#endif
assert(order > 0);
for(i = 0; i < data_len; i++) {
#ifdef FLAC__OVERFLOW_DETECT
sumo = 0;
#endif
sum = 0;
history = data;
for(j = 0; j < order; j++) {
sum += qlp_coeff[j] * (*(--history));
#ifdef FLAC__OVERFLOW_DETECT
sumo += (int64)qlp_coeff[j] * (int64)(*history);
if(sumo > 2147483647ll || sumo < -2147483648ll) {
fprintf(stderr,"FLAC__lpc_compute_residual_from_qlp_coefficients: OVERFLOW, i=%u, j=%u, c=%d, d=%d, sumo=%lld\n",i,j,qlp_coeff[j],*history,sumo);
}
#endif
}
*(residual++) = *(data++) - (sum >> lp_quantization);
}
/* Here's a slower but clearer version:
for(i = 0; i < data_len; i++) {
sum = 0;
for(j = 0; j < order; j++)
sum += qlp_coeff[j] * data[i-j-1];
residual[i] = data[i] - (sum >> lp_quantization);
}
*/
}
void FLAC__lpc_restore_signal(const int32 residual[], unsigned data_len, const int32 qlp_coeff[], unsigned order, int lp_quantization, int32 data[])
{
#ifdef FLAC__OVERFLOW_DETECT
int64 sumo;
#endif
unsigned i, j;
int32 sum;
const int32 *history;
#ifdef FLAC__OVERFLOW_DETECT_VERBOSE
fprintf(stderr,"FLAC__lpc_restore_signal: data_len=%d, order=%u, lpq=%d",data_len,order,lp_quantization);
for(i=0;i<order;i++)
fprintf(stderr,", q[%u]=%d",i,qlp_coeff[i]);
fprintf(stderr,"\n");
#endif
assert(order > 0);
for(i = 0; i < data_len; i++) {
#ifdef FLAC__OVERFLOW_DETECT
sumo = 0;
#endif
sum = 0;
history = data;
for(j = 0; j < order; j++) {
sum += qlp_coeff[j] * (*(--history));
#ifdef FLAC__OVERFLOW_DETECT
sumo += (int64)qlp_coeff[j] * (int64)(*history);
if(sumo > 2147483647ll || sumo < -2147483648ll) {
fprintf(stderr,"FLAC__lpc_restore_signal: OVERFLOW, i=%u, j=%u, c=%d, d=%d, sumo=%lld\n",i,j,qlp_coeff[j],*history,sumo);
}
#endif
}
*(data++) = *(residual++) + (sum >> lp_quantization);
}
/* Here's a slower but clearer version:
for(i = 0; i < data_len; i++) {
sum = 0;
for(j = 0; j < order; j++)
sum += qlp_coeff[j] * data[i-j-1];
data[i] = residual[i] + (sum >> lp_quantization);
}
*/
}
real FLAC__lpc_compute_expected_bits_per_residual_sample(real lpc_error, unsigned total_samples)
{
real error_scale;
assert(total_samples > 0);
error_scale = 0.5 * M_LN2 * M_LN2 / (real)total_samples;
if(lpc_error > 0.0) {
real bps = 0.5 * log(error_scale * lpc_error) / M_LN2;
if(bps >= 0.0)
return bps;
else
return 0.0;
}
else if(lpc_error < 0.0) { /* error should not be negative but can happen due to inadequate float resolution */
return 1e10;
}
else {
return 0.0;
}
}
real FLAC__lpc_compute_expected_bits_per_residual_sample_with_error_scale(real lpc_error, real error_scale)
{
if(lpc_error > 0.0) {
real bps = 0.5 * log(error_scale * lpc_error) / M_LN2;
if(bps >= 0.0)
return bps;
else
return 0.0;
}
else if(lpc_error < 0.0) { /* error should not be negative but can happen due to inadequate float resolution */
return 1e10;
}
else {
return 0.0;
}
}
unsigned FLAC__lpc_compute_best_order(const real lpc_error[], unsigned max_order, unsigned total_samples, unsigned bits_per_signal_sample)
{
unsigned order, best_order;
real best_bits, tmp_bits, error_scale;
assert(max_order > 0);
assert(total_samples > 0);
error_scale = 0.5 * M_LN2 * M_LN2 / (real)total_samples;
best_order = 0;
best_bits = FLAC__lpc_compute_expected_bits_per_residual_sample_with_error_scale(lpc_error[0], error_scale) * (real)total_samples;
for(order = 1; order < max_order; order++) {
tmp_bits = FLAC__lpc_compute_expected_bits_per_residual_sample_with_error_scale(lpc_error[order], error_scale) * (real)(total_samples - order) + (real)(order * bits_per_signal_sample);
if(tmp_bits < best_bits) {
best_order = order;
best_bits = tmp_bits;
}
}
return best_order+1; /* +1 since index of lpc_error[] is order-1 */
}
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