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add dithering to lp coeff quantization

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This commit is contained in:
Josh Coalson
2007-02-02 06:14:41 +00:00
parent f57bd7abbd
commit 0486d4352a
1 changed files with 44 additions and 24 deletions
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68
src/libFLAC/lpc.c
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@@ -152,10 +152,8 @@ void FLAC__lpc_compute_lp_coefficients(const FLAC__real autoc[], unsigned *max_o
int FLAC__lpc_quantize_coefficients(const FLAC__real lp_coeff[], unsigned order, unsigned precision, FLAC__int32 qlp_coeff[], int *shift)
{
unsigned i;
FLAC__double d, cmax = -1e32;
FLAC__double cmax;
FLAC__int32 qmax, qmin;
const int max_shiftlimit = (1 << (FLAC__SUBFRAME_LPC_QLP_SHIFT_LEN-1)) - 1;
const int min_shiftlimit = -max_shiftlimit - 1;
FLAC__ASSERT(precision > 0);
FLAC__ASSERT(precision >= FLAC__MIN_QLP_COEFF_PRECISION);
@@ -166,19 +164,21 @@ int FLAC__lpc_quantize_coefficients(const FLAC__real lp_coeff[], unsigned order,
qmin = -qmax;
qmax--;
/* calc cmax = max( |lp_coeff[i]| ) */
cmax = 0.0;
for(i = 0; i < order; i++) {
if(lp_coeff[i] == 0.0)
continue;
d = fabs(lp_coeff[i]);
const FLAC__double d = fabs(lp_coeff[i]);
if(d > cmax)
cmax = d;
}
redo_it:
if(cmax <= 0.0) {
/* => coefficients are all 0, which means our constant-detect didn't work */
return 2;
}
else {
const int max_shiftlimit = (1 << (FLAC__SUBFRAME_LPC_QLP_SHIFT_LEN-1)) - 1;
const int min_shiftlimit = -max_shiftlimit - 1;
int log2cmax;
(void)frexp(cmax, &log2cmax);
@@ -186,6 +186,9 @@ redo_it:
*shift = (int)precision - log2cmax - 1;
if(*shift < min_shiftlimit || *shift > max_shiftlimit) {
#ifdef FLAC__OVERFLOW_DETECT
fprintf(stderr,"FLAC__lpc_quantize_coefficients: shift out of limit: shift=%d cmax=%f precision=%u\n",q,qmax,*shift,cmax,precision+1);
#endif
#if 0
/*@@@ this does not seem to help at all, but was not extensively tested either: */
if(*shift > max_shiftlimit)
@@ -197,36 +200,53 @@ redo_it:
}
if(*shift >= 0) {
FLAC__double error = 0.0;
FLAC__int32 q;
for(i = 0; i < order; i++) {
qlp_coeff[i] = (FLAC__int32)floor((FLAC__double)lp_coeff[i] * (FLAC__double)(1 << *shift));
/* double-check the result */
if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) {
error += lp_coeff[i] * (1 << *shift);
q = lround(error); /* round() is also suitable */
#ifdef FLAC__OVERFLOW_DETECT
fprintf(stderr,"FLAC__lpc_quantize_coefficients: compensating for overflow, qlp_coeff[%u]=%d, lp_coeff[%u]=%f, cmax=%f, precision=%u, shift=%d, q=%f, f(q)=%f\n", i, qlp_coeff[i], i, lp_coeff[i], cmax, precision, *shift, (FLAC__double)lp_coeff[i] * (FLAC__double)(1 << *shift), floor((FLAC__double)lp_coeff[i] * (FLAC__double)(1 << *shift)));
if(q > qmax)
fprintf(stderr,"FLAC__lpc_quantize_coefficients: quantizer overflow: q>qmax %d>%d shift=%d cmax=%f precision=%u lpc[%u]=%f\n",q,qmax,*shift,cmax,precision+1,i,lp_coeff[i]);
else if(q < qmin)
fprintf(stderr,"FLAC__lpc_quantize_coefficients: quantizer overflow: q<qmin %d<%d shift=%d cmax=%f precision=%u lpc[%u]=%f\n",q,qmin,*shift,cmax,precision+1,i,lp_coeff[i]);
#endif
cmax *= 2.0;
goto redo_it;
}
if(q > qmax)
q = qmax;
else if(q < qmin)
q = qmin;
error -= q;
qlp_coeff[i] = q;
}
}
else { /* (*shift < 0) */
/* negative shift is very rare but due to design flaw, negative shift is
* a NOP in the decoder, so it must be handled specially by scaling down
* coeffs
*/
else {
const int nshift = -(*shift);
FLAC__double error = 0.0;
FLAC__int32 q;
#ifdef DEBUG
fprintf(stderr,"FLAC__lpc_quantize_coefficients: negative shift = %d\n", *shift);
#endif
for(i = 0; i < order; i++) {
qlp_coeff[i] = (FLAC__int32)floor((FLAC__double)lp_coeff[i] / (FLAC__double)(1 << nshift));
/* double-check the result */
if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) {
error += lp_coeff[i] / (1 << nshift);
q = lround(error); /* round() is also suitable */
#ifdef FLAC__OVERFLOW_DETECT
fprintf(stderr,"FLAC__lpc_quantize_coefficients: compensating for overflow, qlp_coeff[%u]=%d, lp_coeff[%u]=%f, cmax=%f, precision=%u, shift=%d, q=%f, f(q)=%f\n", i, qlp_coeff[i], i, lp_coeff[i], cmax, precision, *shift, (FLAC__double)lp_coeff[i] / (FLAC__double)(1 << nshift), floor((FLAC__double)lp_coeff[i] / (FLAC__double)(1 << nshift)));
if(q > qmax)
fprintf(stderr,"FLAC__lpc_quantize_coefficients: quantizer overflow: q>qmax %d>%d shift=%d cmax=%f precision=%u lpc[%u]=%f\n",q,qmax,*shift,cmax,precision+1,i,lp_coeff[i]);
else if(q < qmin)
fprintf(stderr,"FLAC__lpc_quantize_coefficients: quantizer overflow: q<qmin %d<%d shift=%d cmax=%f precision=%u lpc[%u]=%f\n",q,qmin,*shift,cmax,precision+1,i,lp_coeff[i]);
#endif
cmax *= 2.0;
goto redo_it;
}
if(q > qmax)
q = qmax;
else if(q < qmin)
q = qmin;
error -= q;
qlp_coeff[i] = q;
}
*shift = 0;
}
return 0;