huffman.c

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/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
 * July 2003
 *
 * huffman.c - Huffman decoding of transform coefficients
 **************************************************************************************/
 
#include "coder.h"
 
/* helper macros - see comments in hufftabs.c about the format of the huffman tables */
#define GetMaxbits(x)   ((int)( (((unsigned short)(x)) >>  0) & 0x000f))
#define GetHLen(x)      ((int)( (((unsigned short)(x)) >> 12) & 0x000f))
#define GetCWY(x)       ((int)( (((unsigned short)(x)) >>  8) & 0x000f))
#define GetCWX(x)       ((int)( (((unsigned short)(x)) >>  4) & 0x000f))
#define GetSignBits(x)  ((int)( (((unsigned short)(x)) >>  0) & 0x000f))
 
#define GetHLenQ(x)     ((int)( (((unsigned char)(x)) >> 4) & 0x0f))
#define GetCWVQ(x)      ((int)( (((unsigned char)(x)) >> 3) & 0x01))
#define GetCWWQ(x)      ((int)( (((unsigned char)(x)) >> 2) & 0x01))
#define GetCWXQ(x)      ((int)( (((unsigned char)(x)) >> 1) & 0x01))
#define GetCWYQ(x)      ((int)( (((unsigned char)(x)) >> 0) & 0x01))
 
/* apply sign of s to the positive number x (save in MSB, will do two's complement in dequant) */
#define ApplySign(x, s) { (x) |= ((s) & 0x80000000); }
 
/**************************************************************************************
 * Function:    DecodeHuffmanPairs
 *
 * Description: decode 2-way vector Huffman codes in the "bigValues" region of spectrum
 *
 * Inputs:      valid BitStreamInfo struct, pointing to start of pair-wise codes
 *              pointer to xy buffer to received decoded values
 *              number of codewords to decode
 *              index of Huffman table to use
 *              number of bits remaining in bitstream
 *
 * Outputs:     pairs of decoded coefficients in vwxy
 *              updated BitStreamInfo struct
 *
 * Return:      number of bits used, or -1 if out of bits
 *
 * Notes:       assumes that nVals is an even number
 *              si_huff.bit tests every Huffman codeword in every table (though not
 *                necessarily all linBits outputs for x,y > 15)
 **************************************************************************************/
// no improvement with section=data
static int DecodeHuffmanPairs(int *xy, int nVals, int tabIdx, int bitsLeft, unsigned char *buf, int bitOffset)
{
  int i, x, y;
  int cachedBits, padBits, len, startBits, linBits, maxBits, minBits;
  HuffTabType tabType;
  unsigned short cw, *tBase, *tCurr;
  unsigned int cache;
 
  if(nVals <= 0) 
    return 0;
 
  if (bitsLeft < 0)
    return -1;
  startBits = bitsLeft;
 
  tBase = (unsigned short *)(huffTable + huffTabOffset[tabIdx]);
  linBits = huffTabLookup[tabIdx].linBits;
  tabType = huffTabLookup[tabIdx].tabType;
 
  ASSERT(!(nVals & 0x01));
  ASSERT(tabIdx < HUFF_PAIRTABS);
  ASSERT(tabIdx >= 0);
  ASSERT(tabType != invalidTab);
 
  /* initially fill cache with any partial byte */
  cache = 0;
  cachedBits = (8 - bitOffset) & 0x07;
  if (cachedBits)
    cache = (unsigned int)(*buf++) << (32 - cachedBits);
  bitsLeft -= cachedBits;
 
  if (tabType == noBits) {
    /* table 0, no data, x = y = 0 */
    for (i = 0; i < nVals; i+=2) {
      xy[i+0] = 0;
      xy[i+1] = 0;
    }
    return 0;
  } else if (tabType == oneShot) {
    /* single lookup, no escapes */
    maxBits = GetMaxbits(tBase[0]);
    tBase++;
    padBits = 0;
    while (nVals > 0) {
      /* refill cache - assumes cachedBits <= 16 */
      if (bitsLeft >= 16) {
        /* load 2 new bytes into left-justified cache */
        cache |= (unsigned int)(*buf++) << (24 - cachedBits);
        cache |= (unsigned int)(*buf++) << (16 - cachedBits);
        cachedBits += 16;
        bitsLeft -= 16;
      } else {
        /* last time through, pad cache with zeros and drain cache */
        if (cachedBits + bitsLeft <= 0) return -1;
        if (bitsLeft > 0) cache |= (unsigned int)(*buf++) << (24 - cachedBits);
        if (bitsLeft > 8) cache |= (unsigned int)(*buf++) << (16 - cachedBits);
        cachedBits += bitsLeft;
        bitsLeft = 0;
 
        cache &= (signed int)0x80000000 >> (cachedBits - 1);
        padBits = 11;
        cachedBits += padBits;  /* okay if this is > 32 (0's automatically shifted in from right) */
      }
 
      /* largest maxBits = 9, plus 2 for sign bits, so make sure cache has at least 11 bits */
      while (nVals > 0 && cachedBits >= 11 ) {
        cw = tBase[cache >> (32 - maxBits)];
        len = GetHLen(cw);
        cachedBits -= len;
        cache <<= len;
 
        x = GetCWX(cw);   if (x)  {ApplySign(x, cache); cache <<= 1; cachedBits--;}
        y = GetCWY(cw);   if (y)  {ApplySign(y, cache); cache <<= 1; cachedBits--;}
 
        /* ran out of bits - should never have consumed padBits */
        if (cachedBits < padBits)
          return -1;
 
        *xy++ = x;
        *xy++ = y;
        nVals -= 2;
      }
    }
    bitsLeft += (cachedBits - padBits);
    return (startBits - bitsLeft);
  } else if (tabType == loopLinbits || tabType == loopNoLinbits) {
    tCurr = tBase;
    padBits = 0;
    while (nVals > 0) {
      /* refill cache - assumes cachedBits <= 16 */
      if (bitsLeft >= 16) {
        /* load 2 new bytes into left-justified cache */
        cache |= (unsigned int)(*buf++) << (24 - cachedBits);
        cache |= (unsigned int)(*buf++) << (16 - cachedBits);
        cachedBits += 16;
        bitsLeft -= 16;
      } else {
        /* last time through, pad cache with zeros and drain cache */
        if (cachedBits + bitsLeft <= 0) return -1;
        if (bitsLeft > 0) cache |= (unsigned int)(*buf++) << (24 - cachedBits);
        if (bitsLeft > 8) cache |= (unsigned int)(*buf++) << (16 - cachedBits);
        cachedBits += bitsLeft;
        bitsLeft = 0;
 
        cache &= (signed int)0x80000000 >> (cachedBits - 1);
        padBits = 11;
        cachedBits += padBits;  /* okay if this is > 32 (0's automatically shifted in from right) */
      }
 
      /* largest maxBits = 9, plus 2 for sign bits, so make sure cache has at least 11 bits */
      while (nVals > 0 && cachedBits >= 11 ) {
        maxBits = GetMaxbits(tCurr[0]);
        cw = tCurr[(cache >> (32 - maxBits)) + 1];
        len = GetHLen(cw);
        if (!len) {
          cachedBits -= maxBits;
          cache <<= maxBits;
          tCurr += cw;
          continue;
        }
        cachedBits -= len;
        cache <<= len;
      
        x = GetCWX(cw);
        y = GetCWY(cw);
 
        if (x == 15 && tabType == loopLinbits) {
          minBits = linBits + 1 + (y ? 1 : 0);
          if (cachedBits + bitsLeft < minBits)
            return -1;
          while (cachedBits < minBits) {
            cache |= (unsigned int)(*buf++) << (24 - cachedBits);
            cachedBits += 8;
            bitsLeft -= 8;
          }
          if (bitsLeft < 0) {
            cachedBits += bitsLeft;
            bitsLeft = 0;
            cache &= (signed int)0x80000000 >> (cachedBits - 1);
          }
          x += (int)(cache >> (32 - linBits));
          cachedBits -= linBits;
          cache <<= linBits;
        }
        if (x)  {ApplySign(x, cache); cache <<= 1; cachedBits--;}
 
        if (y == 15 && tabType == loopLinbits) {
          minBits = linBits + 1;
          if (cachedBits + bitsLeft < minBits)
            return -1;
          while (cachedBits < minBits) {
            cache |= (unsigned int)(*buf++) << (24 - cachedBits);
            cachedBits += 8;
            bitsLeft -= 8;
          }
          if (bitsLeft < 0) {
            cachedBits += bitsLeft;
            bitsLeft = 0;
            cache &= (signed int)0x80000000 >> (cachedBits - 1);
          }
          y += (int)(cache >> (32 - linBits));
          cachedBits -= linBits;
          cache <<= linBits;
        }
        if (y)  {ApplySign(y, cache); cache <<= 1; cachedBits--;}
 
        /* ran out of bits - should never have consumed padBits */
        if (cachedBits < padBits)
          return -1;
 
        *xy++ = x;
        *xy++ = y;
        nVals -= 2;
        tCurr = tBase;
      }
    }
    bitsLeft += (cachedBits - padBits);
    return (startBits - bitsLeft);
  }
 
  /* error in bitstream - trying to access unused Huffman table */
  return -1;
}
 
/**************************************************************************************
 * Function:    DecodeHuffmanQuads
 *
 * Description: decode 4-way vector Huffman codes in the "count1" region of spectrum
 *
 * Inputs:      valid BitStreamInfo struct, pointing to start of quadword codes
 *              pointer to vwxy buffer to received decoded values
 *              maximum number of codewords to decode
 *              index of quadword table (0 = table A, 1 = table B)
 *              number of bits remaining in bitstream
 *
 * Outputs:     quadruples of decoded coefficients in vwxy
 *              updated BitStreamInfo struct
 *
 * Return:      index of the first "zero_part" value (index of the first sample 
 *                of the quad word after which all samples are 0)
 * 
 * Notes:        si_huff.bit tests every vwxy output in both quad tables
 **************************************************************************************/
// no improvement with section=data
static int DecodeHuffmanQuads(int *vwxy, int nVals, int tabIdx, int bitsLeft, unsigned char *buf, int bitOffset)
{
  int i, v, w, x, y;
  int len, maxBits, cachedBits, padBits;
  unsigned int cache;
  unsigned char cw, *tBase;
 
  if (bitsLeft <= 0)
    return 0;
 
  tBase = (unsigned char *)quadTable + quadTabOffset[tabIdx];
  maxBits = quadTabMaxBits[tabIdx];
 
  /* initially fill cache with any partial byte */
  cache = 0;
  cachedBits = (8 - bitOffset) & 0x07;
  if (cachedBits)
    cache = (unsigned int)(*buf++) << (32 - cachedBits);
  bitsLeft -= cachedBits;
 
  i = padBits = 0;
  while (i < (nVals - 3)) {
    /* refill cache - assumes cachedBits <= 16 */
    if (bitsLeft >= 16) {
      /* load 2 new bytes into left-justified cache */
      cache |= (unsigned int)(*buf++) << (24 - cachedBits);
      cache |= (unsigned int)(*buf++) << (16 - cachedBits);
      cachedBits += 16;
      bitsLeft -= 16;
    } else {
      /* last time through, pad cache with zeros and drain cache */
      if (cachedBits + bitsLeft <= 0) return i;
      if (bitsLeft > 0) cache |= (unsigned int)(*buf++) << (24 - cachedBits);
      if (bitsLeft > 8) cache |= (unsigned int)(*buf++) << (16 - cachedBits);
      cachedBits += bitsLeft;
      bitsLeft = 0;
 
      cache &= (signed int)0x80000000 >> (cachedBits - 1);
      padBits = 10;
      cachedBits += padBits;  /* okay if this is > 32 (0's automatically shifted in from right) */
    }
 
    /* largest maxBits = 6, plus 4 for sign bits, so make sure cache has at least 10 bits */
    while (i < (nVals - 3) && cachedBits >= 10 ) {
      cw = tBase[cache >> (32 - maxBits)];
      len = GetHLenQ(cw);
      cachedBits -= len;
      cache <<= len;
 
      v = GetCWVQ(cw);  if(v) {ApplySign(v, cache); cache <<= 1; cachedBits--;}
      w = GetCWWQ(cw);  if(w) {ApplySign(w, cache); cache <<= 1; cachedBits--;}
      x = GetCWXQ(cw);  if(x) {ApplySign(x, cache); cache <<= 1; cachedBits--;}
      y = GetCWYQ(cw);  if(y) {ApplySign(y, cache); cache <<= 1; cachedBits--;}
 
      /* ran out of bits - okay (means we're done) */
      if (cachedBits < padBits)
        return i;
 
      *vwxy++ = v;
      *vwxy++ = w;
      *vwxy++ = x;
      *vwxy++ = y;
      i += 4;
    }
  }
 
  /* decoded max number of quad values */
  return i;
}
 
/**************************************************************************************
 * Function:    DecodeHuffman
 *
 * Description: decode one granule, one channel worth of Huffman codes
 *
 * Inputs:      MP3DecInfo structure filled by UnpackFrameHeader(), UnpackSideInfo(),
 *                and UnpackScaleFactors() (for this granule)
 *              buffer pointing to start of Huffman data in MP3 frame
 *              pointer to bit offset (0-7) indicating starting bit in buf[0]
 *              number of bits in the Huffman data section of the frame
 *                (could include padding bits)
 *              index of current granule and channel
 *
 * Outputs:     decoded coefficients in hi->huffDecBuf[ch] (hi pointer in mp3DecInfo)
 *              updated bitOffset
 *
 * Return:      length (in bytes) of Huffman codes
 *              bitOffset also returned in parameter (0 = MSB, 7 = LSB of 
 *                byte located at buf + offset)
 *              -1 if null input pointers, huffBlockBits < 0, or decoder runs 
 *                out of bits prematurely (invalid bitstream)
 **************************************************************************************/
// .data about 1ms faster per frame
int DecodeHuffman(MP3DecInfo *mp3DecInfo, unsigned char *buf, int *bitOffset, int huffBlockBits, int gr, int ch)
{
  int r1Start, r2Start, rEnd[4];  /* region boundaries */
  int i, w, bitsUsed, bitsLeft;
  unsigned char *startBuf = buf;
 
  FrameHeader *fh;
  SideInfo *si;
  SideInfoSub *sis;
  HuffmanInfo *hi;
 
  /* validate pointers */
  if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->ScaleFactorInfoPS || !mp3DecInfo->HuffmanInfoPS)
    return -1;
 
  fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
  si = ((SideInfo *)(mp3DecInfo->SideInfoPS));
  sis = &si->sis[gr][ch];
  hi = (HuffmanInfo*)(mp3DecInfo->HuffmanInfoPS);
 
  if (huffBlockBits < 0)
    return -1;
 
  /* figure out region boundaries (the first 2*bigVals coefficients divided into 3 regions) */
  if (sis->winSwitchFlag && sis->blockType == 2) {
    if (sis->mixedBlock == 0) {
      r1Start = fh->sfBand->s[(sis->region0Count + 1)/3] * 3;
    } else {
      if (fh->ver == MPEG1) {
        r1Start = fh->sfBand->l[sis->region0Count + 1];
      } else {
        /* see MPEG2 spec for explanation */
        w = fh->sfBand->s[4] - fh->sfBand->s[3];
        r1Start = fh->sfBand->l[6] + 2*w;
      }
    }
    r2Start = MAX_NSAMP;  /* short blocks don't have region 2 */
  } else {
    r1Start = fh->sfBand->l[sis->region0Count + 1];
    r2Start = fh->sfBand->l[sis->region0Count + 1 + sis->region1Count + 1];
  }
 
  /* offset rEnd index by 1 so first region = rEnd[1] - rEnd[0], etc. */
  rEnd[3] = MIN(MAX_NSAMP, 2 * sis->nBigvals);
  rEnd[2] = MIN(r2Start, rEnd[3]);
  rEnd[1] = MIN(r1Start, rEnd[3]);
  rEnd[0] = 0;
 
  /* rounds up to first all-zero pair (we don't check last pair for (x,y) == (non-zero, zero)) */
  hi->nonZeroBound[ch] = rEnd[3];
 
  /* decode Huffman pairs (rEnd[i] are always even numbers) */
  bitsLeft = huffBlockBits;
  for (i = 0; i < 3; i++) {
    bitsUsed = DecodeHuffmanPairs(hi->huffDecBuf[ch] + rEnd[i], rEnd[i+1] - rEnd[i], sis->tableSelect[i], bitsLeft, buf, *bitOffset);
    if (bitsUsed < 0 || bitsUsed > bitsLeft)  /* error - overran end of bitstream */
      return -1;
 
    /* update bitstream position */
    buf += (bitsUsed + *bitOffset) >> 3;
    *bitOffset = (bitsUsed + *bitOffset) & 0x07;
    bitsLeft -= bitsUsed;
  }
 
  /* decode Huffman quads (if any) */
  hi->nonZeroBound[ch] += DecodeHuffmanQuads(hi->huffDecBuf[ch] + rEnd[3], MAX_NSAMP - rEnd[3], sis->count1TableSelect, bitsLeft, buf, *bitOffset);
 
  ASSERT(hi->nonZeroBound[ch] <= MAX_NSAMP);
  for (i = hi->nonZeroBound[ch]; i < MAX_NSAMP; i++)
    hi->huffDecBuf[ch][i] = 0;
  
  /* If bits used for 576 samples < huffBlockBits, then the extras are considered
   *  to be stuffing bits (throw away, but need to return correct bitstream position) 
   */
  buf += (bitsLeft + *bitOffset) >> 3;
  *bitOffset = (bitsLeft + *bitOffset) & 0x07;
  
  return (int)(buf - startBuf);
}