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switch to better method for getting floor(log2(double))

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This commit is contained in:
Josh Coalson
2001-07-19 17:07:13 +00:00
parent aeeaa1b3d5
commit 8c6f90f1aa
1 changed files with 6 additions and 5 deletions
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11
src/libFLAC/lpc.c
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@@ -145,10 +145,11 @@ redo_it:
return 2; return 2;
} }
else { else {
const int log2cmax = (int)floor(log(cmax) / M_LN2); /* this is a good estimate but may not be precise enough, so we have to check for corner cases later when shifting */ int log2cmax;
const int maxshift = (int)precision - log2cmax - 1;
*shift = maxshift; (void)frexp(cmax, &log2cmax);
log2cmax--;
*shift = (int)precision - log2cmax - 1;
if(*shift < min_shiftlimit || *shift > max_shiftlimit) { if(*shift < min_shiftlimit || *shift > max_shiftlimit) {
return 1; return 1;
@@ -159,7 +160,7 @@ redo_it:
for(i = 0; i < order; i++) { for(i = 0; i < order; i++) {
qlp_coeff[i] = (FLAC__int32)floor((double)lp_coeff[i] * (double)(1 << *shift)); qlp_coeff[i] = (FLAC__int32)floor((double)lp_coeff[i] * (double)(1 << *shift));
/* check for corner cases mentioned in the comment for log2cmax above */ /* double-check the result */
if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) { if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) {
#ifdef FLAC__OVERFLOW_DETECT #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, (double)lp_coeff[i] * (double)(1 << *shift), floor((double)lp_coeff[i] * (double)(1 << *shift))); 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, (double)lp_coeff[i] * (double)(1 << *shift), floor((double)lp_coeff[i] * (double)(1 << *shift)));
@@ -177,7 +178,7 @@ redo_it:
for(i = 0; i < order; i++) { for(i = 0; i < order; i++) {
qlp_coeff[i] = (FLAC__int32)floor((double)lp_coeff[i] / (double)(1 << nshift)); qlp_coeff[i] = (FLAC__int32)floor((double)lp_coeff[i] / (double)(1 << nshift));
/* check for corner cases mentioned in the comment for log2cmax above */ /* double-check the result */
if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) { if(qlp_coeff[i] > qmax || qlp_coeff[i] < qmin) {
#ifdef FLAC__OVERFLOW_DETECT #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, (double)lp_coeff[i] / (double)(1 << nshift), floor((double)lp_coeff[i] / (double)(1 << nshift))); 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, (double)lp_coeff[i] / (double)(1 << nshift), floor((double)lp_coeff[i] / (double)(1 << nshift)));