IMDCT() [2/2]

int32_t fl::third_party::IMDCT	(	MP3DecInfo *	mp3DecInfo,
		int32_t	gr,
		int32_t	ch )

Definition at line 736 of file imdct.hpp.

{
    int32_t nBfly, blockCutoff;
    FrameHeader *fh;
    SideInfo *si;
    HuffmanInfo *hi;
    IMDCTInfo *mi;
    BlockCount bc;
 
    /* validate pointers */
    if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || 
        !mp3DecInfo->HuffmanInfoPS || !mp3DecInfo->IMDCTInfoPS)
        return -1;
 
    /* si is an array of up to 4 structs, stored as gr0ch0, gr0ch1, gr1ch0, gr1ch1 */
    fh = (FrameHeader *)(mp3DecInfo->FrameHeaderPS);
    si = (SideInfo *)(mp3DecInfo->SideInfoPS);
    hi = (HuffmanInfo*)(mp3DecInfo->HuffmanInfoPS);
    mi = (IMDCTInfo *)(mp3DecInfo->IMDCTInfoPS);
 
    /* anti-aliasing done on whole long blocks only
     * for mixed blocks, nBfly always 1, except 3 for 8 kHz MPEG 2.5 (see sfBandTab) 
     *   nLongBlocks = number of blocks with (possibly) non-zero power 
     *   nBfly = number of butterflies to do (nLongBlocks - 1, unless no long blocks)
     */
    blockCutoff = fh->sfBand->l[(fh->ver == MPEG1 ? 8 : 6)] / 18;    /* same as 3* num short sfb's in spec */
    if (si->sis[gr][ch].blockType != 2) {
        /* all long transforms */
        bc.nBlocksLong = MIN((hi->nonZeroBound[ch] + 7) / 18 + 1, 32);    
        nBfly = bc.nBlocksLong - 1;
    } else if (si->sis[gr][ch].blockType == 2 && si->sis[gr][ch].mixedBlock) {
        /* mixed block - long transforms until cutoff, then short transforms */
        bc.nBlocksLong = blockCutoff;    
        nBfly = bc.nBlocksLong - 1;
    } else {
        /* all short transforms */
        bc.nBlocksLong = 0;
        nBfly = 0;
    }
 
    AntiAlias(hi->huffDecBuf[ch], nBfly);
    hi->nonZeroBound[ch] = MAX(hi->nonZeroBound[ch], (nBfly * 18) + 8);
 
    ASSERT(hi->nonZeroBound[ch] <= MAX_NSAMP);
 
    /* for readability, use a struct instead of passing a million parameters to HybridTransform() */
    bc.nBlocksTotal = (hi->nonZeroBound[ch] + 17) / 18;
    bc.nBlocksPrev = mi->numPrevIMDCT[ch];
    bc.prevType = mi->prevType[ch];
    bc.prevWinSwitch = mi->prevWinSwitch[ch];
    bc.currWinSwitch = (si->sis[gr][ch].mixedBlock ? blockCutoff : 0);    /* where WINDOW switches (not nec. transform) */
    bc.gbIn = hi->gb[ch];
 
    mi->numPrevIMDCT[ch] = HybridTransform(hi->huffDecBuf[ch], mi->overBuf[ch], mi->outBuf[ch], &si->sis[gr][ch], &bc);
    mi->prevType[ch] = si->sis[gr][ch].blockType;
    mi->prevWinSwitch[ch] = bc.currWinSwitch;     /* 0 means not a mixed block (either all short or all long) */
    mi->gb[ch] = bc.gbOut;
 
    ASSERT(mi->numPrevIMDCT[ch] <= NBANDS);
 
    /* output has gained 2 int bits */
    return 0;
}

References AntiAlias(), ASSERT, fl::third_party::_SideInfoSub::blockType, fl::third_party::_BlockCount::currWinSwitch, FL_NOEXCEPT, fl::third_party::_HuffmanInfo::gb, fl::third_party::_IMDCTInfo::gb, fl::third_party::_BlockCount::gbIn, fl::third_party::_BlockCount::gbOut, fl::third_party::_HuffmanInfo::huffDecBuf, HybridTransform(), fl::third_party::_SFBandTable::l, MAX, MAX_NSAMP, MIN, fl::third_party::_SideInfoSub::mixedBlock, MPEG1, NBANDS, fl::third_party::_BlockCount::nBlocksLong, fl::third_party::_BlockCount::nBlocksPrev, fl::third_party::_BlockCount::nBlocksTotal, fl::third_party::_HuffmanInfo::nonZeroBound, fl::third_party::_IMDCTInfo::numPrevIMDCT, fl::third_party::_IMDCTInfo::outBuf, fl::third_party::_IMDCTInfo::overBuf, fl::third_party::_BlockCount::prevType, fl::third_party::_IMDCTInfo::prevType, fl::third_party::_BlockCount::prevWinSwitch, fl::third_party::_IMDCTInfo::prevWinSwitch, fl::third_party::_FrameHeader::sfBand, fl::third_party::_SideInfo::sis, and fl::third_party::_FrameHeader::ver.

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