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/**************************************************************************************
* Fixed-point MP3 decoder
* Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
* June 2003
*
* dequant.c - dequantization, stereo processing (intensity, mid-side), short-block
* coefficient reordering
**************************************************************************************/
#include "coder.h"
#include "assembly.h"
/**************************************************************************************
* Function: Dequantize
*
* Description: dequantize coefficients, decode stereo, reorder short blocks
* (one granule-worth)
*
* Inputs: MP3DecInfo structure filled by UnpackFrameHeader(), UnpackSideInfo(),
* UnpackScaleFactors(), and DecodeHuffman() (for this granule)
* index of current granule
*
* Outputs: dequantized and reordered coefficients in hi->huffDecBuf
* (one granule-worth, all channels), format = Q26
* operates in-place on huffDecBuf but also needs di->workBuf
* updated hi->nonZeroBound index for both channels
*
* Return: 0 on success, -1 if null input pointers
*
* Notes: In calling output Q(DQ_FRACBITS_OUT), we assume an implicit bias
* of 2^15. Some (floating-point) reference implementations factor this
* into the 2^(0.25 * gain) scaling explicitly. But to avoid precision
* loss, we don't do that. Instead take it into account in the final
* round to PCM (>> by 15 less than we otherwise would have).
* Equivalently, we can think of the dequantized coefficients as
* Q(DQ_FRACBITS_OUT - 15) with no implicit bias.
**************************************************************************************/
int Dequantize(MP3DecInfo *mp3DecInfo, int gr)
{
int i, ch, nSamps, mOut[2];
FrameHeader *fh;
SideInfo *si;
ScaleFactorInfo *sfi;
HuffmanInfo *hi;
DequantInfo *di;
CriticalBandInfo *cbi;
/* validate pointers */
if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->ScaleFactorInfoPS ||
!mp3DecInfo->HuffmanInfoPS || !mp3DecInfo->DequantInfoPS)
return -1;
fh = (FrameHeader *)(mp3DecInfo->FrameHeaderPS);
/* si is an array of up to 4 structs, stored as gr0ch0, gr0ch1, gr1ch0, gr1ch1 */
si = (SideInfo *)(mp3DecInfo->SideInfoPS);
sfi = (ScaleFactorInfo *)(mp3DecInfo->ScaleFactorInfoPS);
hi = (HuffmanInfo *)mp3DecInfo->HuffmanInfoPS;
di = (DequantInfo *)mp3DecInfo->DequantInfoPS;
cbi = di->cbi;
mOut[0] = mOut[1] = 0;
/* dequantize all the samples in each channel */
for (ch = 0; ch < mp3DecInfo->nChans; ch++) {
hi->gb[ch] = DequantChannel(hi->huffDecBuf[ch], di->workBuf, &hi->nonZeroBound[ch], fh,
&si->sis[gr][ch], &sfi->sfis[gr][ch], &cbi[ch]);
}
/* joint stereo processing assumes one guard bit in input samples
* it's extremely rare not to have at least one gb, so if this is the case
* just make a pass over the data and clip to [-2^30+1, 2^30-1]
* in practice this may never happen
*/
if (fh->modeExt && (hi->gb[0] < 1 || hi->gb[1] < 1)) {
for (i = 0; i < hi->nonZeroBound[0]; i++) {
if (hi->huffDecBuf[0][i] < -0x3fffffff) hi->huffDecBuf[0][i] = -0x3fffffff;
if (hi->huffDecBuf[0][i] > 0x3fffffff) hi->huffDecBuf[0][i] = 0x3fffffff;
}
for (i = 0; i < hi->nonZeroBound[1]; i++) {
if (hi->huffDecBuf[1][i] < -0x3fffffff) hi->huffDecBuf[1][i] = -0x3fffffff;
if (hi->huffDecBuf[1][i] > 0x3fffffff) hi->huffDecBuf[1][i] = 0x3fffffff;
}
}
/* do mid-side stereo processing, if enabled */
if (fh->modeExt >> 1) {
if (fh->modeExt & 0x01) {
/* intensity stereo enabled - run mid-side up to start of right zero region */
if (cbi[1].cbType == 0)
nSamps = fh->sfBand->l[cbi[1].cbEndL + 1];
else
nSamps = 3 * fh->sfBand->s[cbi[1].cbEndSMax + 1];
} else {
/* intensity stereo disabled - run mid-side on whole spectrum */
nSamps = MAX(hi->nonZeroBound[0], hi->nonZeroBound[1]);
}
MidSideProc(hi->huffDecBuf, nSamps, mOut);
}
/* do intensity stereo processing, if enabled */
if (fh->modeExt & 0x01) {
nSamps = hi->nonZeroBound[0];
if (fh->ver == MPEG1) {
IntensityProcMPEG1(hi->huffDecBuf, nSamps, fh, &sfi->sfis[gr][1], di->cbi,
fh->modeExt >> 1, si->sis[gr][1].mixedBlock, mOut);
} else {
IntensityProcMPEG2(hi->huffDecBuf, nSamps, fh, &sfi->sfis[gr][1], di->cbi, &sfi->sfjs,
fh->modeExt >> 1, si->sis[gr][1].mixedBlock, mOut);
}
}
/* adjust guard bit count and nonZeroBound if we did any stereo processing */
if (fh->modeExt) {
hi->gb[0] = CLZ(mOut[0]) - 1;
hi->gb[1] = CLZ(mOut[1]) - 1;
nSamps = MAX(hi->nonZeroBound[0], hi->nonZeroBound[1]);
hi->nonZeroBound[0] = nSamps;
hi->nonZeroBound[1] = nSamps;
}
/* output format Q(DQ_FRACBITS_OUT) */
return 0;
}