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rework LPC coefficient quantizer

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This commit is contained in:
Josh Coalson 2001-02-28 23:56:03 +00:00
parent 74ce843cb7
commit c625f9033c
2 changed files with 69 additions and 13 deletions
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14
src/libFLAC/include/private/lpc.h
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@ -71,15 +71,15 @@ void FLAC__lpc_compute_lp_coefficients(const real autoc[], unsigned max_order, r
* bit) of largest coefficient
* IN bits_per_sample > 0 bits per sample of the originial signal
* OUT qlp_coeff[0,order-1] quantized coefficients
* OUT bits # of bits to shift right to get approximated
* LP coefficients. NOTE: could be negative,
* but |*bits| will always be <= precision
* OUT shift # of bits to shift right to get approximated
* LP coefficients. NOTE: could be negative.
* RETURN 0 => quantization OK
* 1 => coefficients vary too much to quantize to the desired
* precision. 'bits' is unset
* 2 => coefficients are all zero, which is bad. 'bits' is unset
* 1 => coefficients require too much shifting for *shift to
* fit in the LPC subframe header. 'shift' is unset.
* 2 => coefficients are all zero, which is bad. 'shift' is
* unset.
*/
int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsigned precision, unsigned bits_per_sample, int32 qlp_coeff[], int *bits);
int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsigned precision, unsigned bits_per_sample, int32 qlp_coeff[], int *shift);
/*
* FLAC__lpc_compute_residual_from_qlp_coefficients()

68
src/libFLAC/lpc.c
View File

@ -80,7 +80,8 @@ void FLAC__lpc_compute_lp_coefficients(const real autoc[], unsigned max_order, r
}
}
int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsigned precision, unsigned bits_per_sample, int32 qlp_coeff[], int *bits)
#if 0
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, rprecision = (real)precision, maxlog = -1e99, minlog = 1e99;
@ -109,15 +110,70 @@ int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsig
else if((rprecision-1.0) - maxlog >= (real)(precision+1))
rprecision = (real)precision + maxlog + 1.0;
*bits = (int)floor((rprecision-1.0) - maxlog); /* '-1' because bits can be negative and the sign bit costs 1 bit */
if(*bits > (int)precision || *bits <= -(int)precision) {
fprintf(stderr, "@@@ FLAC__lpc_quantize_coefficients(): ERROR: *bits=%d, maxlog=%f, minlog=%f, precision=%u, rprecision=%f\n", *bits, maxlog, minlog, precision, rprecision);
*shift = (int)floor((rprecision-1.0) - maxlog); /* '-1' because *shift can be negative and the sign bit costs 1 bit */
if(*shift > (int)precision || *shift <= -(int)precision) {
fprintf(stderr, "@@@ FLAC__lpc_quantize_coefficients(): ERROR: *shift=%d, maxlog=%f, minlog=%f, precision=%u, rprecision=%f\n", *shift, maxlog, minlog, precision, rprecision);
return 1;
}
if(*bits != 0) { /* just to avoid wasting time... */
if(*shift != 0) { /* just to avoid wasting time... */
for(i = 0; i < order; i++)
qlp_coeff[i] = (int32)floor(lp_coeff[i] * (real)(1 << *bits));
qlp_coeff[i] = (int32)floor(lp_coeff[i] * (real)(1 << *shift));
}
return 0;
}
#endif
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 = -1e99;//@@@, cmin = 1e99;
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 = fabs(lp_coeff[i]);
if(d > cmax)
cmax = d;
//@@@ if(d < cmin)
//@@@ cmin = d;
}
//@@@ if(cmax < cmin)
if(cmax < 0) {
/* => coeffients are all 0, which means our constant-detect didn't work */
fprintf(stderr,"@@@ LPCQ ERROR, all lpc_coeffs are 0\n");
return 2;
}
else {
//@@@ const int minshift = (int)precision - floor(log(cmin) / M_LN2) - 1;
const int maxshift = (int)precision - floor(log(cmax) / M_LN2) - 1;
//@@@ assert(maxshift >= minshift);
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) {
fprintf(stderr,"@@@ LPCQ ERROR, shift is outside shiftlimit\n");
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;
}