dqchan.c

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/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
 * August 2003
 *
 * dqchan.c - dequantization of transform coefficients
 **************************************************************************************/
 
#include "coder.h"
#include "assembly.h"
 
typedef int ARRAY3[3];  /* for short-block reordering */
 
/* optional pre-emphasis for high-frequency scale factor bands */
static const char preTab[22] = { 0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,2,2,3,3,3,2,0 };
 
/* pow(2,-i/4) for i=0..3, Q31 format */
int pow14[4] = { 
  0x7fffffff, 0x6ba27e65, 0x5a82799a, 0x4c1bf829
};
 
/* pow(2,-i/4) * pow(j,4/3) for i=0..3 j=0..15, Q25 format */
int pow43_14[4][16] = {
{ 0x00000000, 0x10000000, 0x285145f3, 0x453a5cdb, /* Q28 */
  0x0cb2ff53, 0x111989d6, 0x15ce31c8, 0x1ac7f203, 
  0x20000000, 0x257106b9, 0x2b16b4a3, 0x30ed74b4, 
  0x36f23fa5, 0x3d227bd3, 0x437be656, 0x49fc823c, },
 
{ 0x00000000, 0x0d744fcd, 0x21e71f26, 0x3a36abd9, 
  0x0aadc084, 0x0e610e6e, 0x12560c1d, 0x168523cf, 
  0x1ae89f99, 0x1f7c03a4, 0x243bae49, 0x29249c67, 
  0x2e34420f, 0x33686f85, 0x38bf3dff, 0x3e370182, },
 
{ 0x00000000, 0x0b504f33, 0x1c823e07, 0x30f39a55, 
  0x08facd62, 0x0c176319, 0x0f6b3522, 0x12efe2ad, 
  0x16a09e66, 0x1a79a317, 0x1e77e301, 0x2298d5b4, 
  0x26da56fc, 0x2b3a902a, 0x2fb7e7e7, 0x3450f650, },
 
{ 0x00000000, 0x09837f05, 0x17f910d7, 0x2929c7a9, 
  0x078d0dfa, 0x0a2ae661, 0x0cf73154, 0x0fec91cb, 
  0x1306fe0a, 0x16434a6c, 0x199ee595, 0x1d17ae3d, 
  0x20abd76a, 0x2459d551, 0x28204fbb, 0x2bfe1808, },
};
 
/* pow(j,4/3) for j=16..63, Q23 format */
int pow43[] = {
  0x1428a2fa, 0x15db1bd6, 0x1796302c, 0x19598d85, 
  0x1b24e8bb, 0x1cf7fcfa, 0x1ed28af2, 0x20b4582a, 
  0x229d2e6e, 0x248cdb55, 0x26832fda, 0x28800000, 
  0x2a832287, 0x2c8c70a8, 0x2e9bc5d8, 0x30b0ff99, 
  0x32cbfd4a, 0x34eca001, 0x3712ca62, 0x393e6088, 
  0x3b6f47e0, 0x3da56717, 0x3fe0a5fc, 0x4220ed72, 
  0x44662758, 0x46b03e7c, 0x48ff1e87, 0x4b52b3f3, 
  0x4daaebfd, 0x5007b497, 0x5268fc62, 0x54ceb29c, 
  0x5738c721, 0x59a72a59, 0x5c19cd35, 0x5e90a129, 
  0x610b9821, 0x638aa47f, 0x660db90f, 0x6894c90b, 
  0x6b1fc80c, 0x6daeaa0d, 0x70416360, 0x72d7e8b0, 
  0x75722ef9, 0x78102b85, 0x7ab1d3ec, 0x7d571e09, 
};
 
/* sqrt(0.5) in Q31 format */
#define SQRTHALF 0x5a82799a
 
/*
 * Minimax polynomial approximation to pow(x, 4/3), over the range
 *  poly43lo: x = [0.5, 0.7071]
 *  poly43hi: x = [0.7071, 1.0]
 *
 * Relative error < 1E-7
 * Coefs are scaled by 4, 2, 1, 0.5, 0.25
 */
int poly43lo[5] = { 0x29a0bda9, 0xb02e4828, 0x5957aa1b, 0x236c498d, 0xff581859 };
int poly43hi[5] = { 0x10852163, 0xd333f6a4, 0x46e9408b, 0x27c2cef0, 0xfef577b4 };
 
/* pow(2, i*4/3) as exp and frac */
int pow2exp[8]  = { 14, 13, 11, 10, 9, 7, 6, 5 };
 
int pow2frac[8] = {
  0x6597fa94, 0x50a28be6, 0x7fffffff, 0x6597fa94, 
  0x50a28be6, 0x7fffffff, 0x6597fa94, 0x50a28be6
};
 
/**************************************************************************************
 * Function:    DequantBlock
 *
 * Description: Ken's highly-optimized, low memory dequantizer performing the operation
 *              y = pow(x, 4.0/3.0) * pow(2, 25 - scale/4.0)
 *
 * Inputs:      input buffer of decode Huffman codewords (signed-magnitude)
 *              output buffer of same length (in-place (outbuf = inbuf) is allowed)
 *              number of samples
 *              
 * Outputs:     dequantized samples in Q25 format
 *
 * Return:      bitwise-OR of the unsigned outputs (for guard bit calculations)
 **************************************************************************************/
static int DequantBlock(int *inbuf, int *outbuf, int num, int scale)
{
  int tab4[4];
  int scalef, scalei, shift;
  int sx, x, y;
  int mask = 0;
  const int *tab16, *coef;
 
  tab16 = pow43_14[scale & 0x3];
  scalef = pow14[scale & 0x3];
  scalei = MIN(scale >> 2, 31); /* smallest input scale = -47, so smallest scalei = -12 */
 
  /* cache first 4 values */
  shift = MIN(scalei + 3, 31);
  shift = MAX(shift, 0);
  tab4[0] = 0;
  tab4[1] = tab16[1] >> shift;
  tab4[2] = tab16[2] >> shift;
  tab4[3] = tab16[3] >> shift;
 
  do {
 
    sx = *inbuf++;
    x = sx & 0x7fffffff;  /* sx = sign|mag */
 
    if (x < 4) {
 
      y = tab4[x];
 
    } else if (x < 16) {
 
      y = tab16[x];
      y = (scalei < 0) ? y << -scalei : y >> scalei;
 
    } else {
 
      if (x < 64) {
 
        y = pow43[x-16];
 
        /* fractional scale */
        y = MULSHIFT32(y, scalef);
        shift = scalei - 3;
 
      } else {
 
        /* normalize to [0x40000000, 0x7fffffff] */
        x <<= 17;
        shift = 0;
        if (x < 0x08000000)
          x <<= 4, shift += 4;
        if (x < 0x20000000)
          x <<= 2, shift += 2;
        if (x < 0x40000000)
          x <<= 1, shift += 1;
 
        coef = (x < SQRTHALF) ? poly43lo : poly43hi;
 
        /* polynomial */
        y = coef[0];
        y = MULSHIFT32(y, x) + coef[1];
        y = MULSHIFT32(y, x) + coef[2];
        y = MULSHIFT32(y, x) + coef[3];
        y = MULSHIFT32(y, x) + coef[4];
        y = MULSHIFT32(y, pow2frac[shift]) << 3;
 
        /* fractional scale */
        y = MULSHIFT32(y, scalef);
        shift = scalei - pow2exp[shift];
      }
 
      /* integer scale */
      if (shift < 0) {
        shift = -shift;
        if (y > (0x7fffffff >> shift))
          y = 0x7fffffff;   /* clip */
        else
          y <<= shift;
      } else {
        y >>= shift;
      }
    }
 
    /* sign and store */
    mask |= y;
    *outbuf++ = (sx < 0) ? -y : y;
 
  } while (--num);
 
  return mask;
}
 
/**************************************************************************************
 * Function:    DequantChannel
 *
 * Description: dequantize one granule, one channel worth of decoded Huffman codewords
 *
 * Inputs:      sample buffer (decoded Huffman codewords), length = MAX_NSAMP samples
 *              work buffer for reordering short-block, length = MAX_REORDER_SAMPS
 *                samples (3 * width of largest short-block critical band)
 *              non-zero bound for this channel/granule
 *              valid FrameHeader, SideInfoSub, ScaleFactorInfoSub, and CriticalBandInfo
 *                structures for this channel/granule
 *
 * Outputs:     MAX_NSAMP dequantized samples in sampleBuf
 *              updated non-zero bound (indicating which samples are != 0 after DQ)
 *              filled-in cbi structure indicating start and end critical bands
 *
 * Return:      minimum number of guard bits in dequantized sampleBuf
 *
 * Notes:       dequantized samples in Q(DQ_FRACBITS_OUT) format 
 **************************************************************************************/
int DequantChannel(int *sampleBuf, int *workBuf, int *nonZeroBound, FrameHeader *fh, SideInfoSub *sis, 
          ScaleFactorInfoSub *sfis, CriticalBandInfo *cbi)
{
  int i, j, w, cb;
  int cbEndL, cbStartS, cbEndS;
  int nSamps, nonZero, sfactMultiplier, gbMask;
  int globalGain, gainI;
  int cbMax[3];
  ARRAY3 *buf;    /* short block reorder */
  
  /* set default start/end points for short/long blocks - will update with non-zero cb info */
  if (sis->blockType == 2) {
    if (sis->mixedBlock) { 
      cbEndL = (fh->ver == MPEG1 ? 8 : 6); 
      cbStartS = 3; 
    } else {
      cbEndL = 0; 
      cbStartS = 0;
    }
    cbEndS = 13;
  } else {
    /* long block */
    cbEndL =   22;
    cbStartS = 13;
    cbEndS =   13;
  }
  cbMax[2] = cbMax[1] = cbMax[0] = 0;
  gbMask = 0;
  i = 0;
 
  /* sfactScale = 0 --> quantizer step size = 2
   * sfactScale = 1 --> quantizer step size = sqrt(2)
   *   so sfactMultiplier = 2 or 4 (jump through globalGain by powers of 2 or sqrt(2))
   */
  sfactMultiplier = 2 * (sis->sfactScale + 1);
 
  /* offset globalGain by -2 if midSide enabled, for 1/sqrt(2) used in MidSideProc()
   *  (DequantBlock() does 0.25 * gainI so knocking it down by two is the same as 
   *   dividing every sample by sqrt(2) = multiplying by 2^-.5)
   */
  globalGain = sis->globalGain;
  if (fh->modeExt >> 1)
     globalGain -= 2;
  globalGain += IMDCT_SCALE;    /* scale everything by sqrt(2), for fast IMDCT36 */
 
  /* long blocks */
  for (cb = 0; cb < cbEndL; cb++) {
 
    nonZero = 0;
    nSamps = fh->sfBand->l[cb + 1] - fh->sfBand->l[cb];
    gainI = 210 - globalGain + sfactMultiplier * (sfis->l[cb] + (sis->preFlag ? (int)preTab[cb] : 0));
 
    nonZero |= DequantBlock(sampleBuf + i, sampleBuf + i, nSamps, gainI);
    i += nSamps;
 
    /* update highest non-zero critical band */
    if (nonZero) 
      cbMax[0] = cb;
    gbMask |= nonZero;
 
    if (i >= *nonZeroBound) 
      break;
  }
 
  /* set cbi (Type, EndS[], EndSMax will be overwritten if we proceed to do short blocks) */
  cbi->cbType = 0;      /* long only */
  cbi->cbEndL  = cbMax[0];
  cbi->cbEndS[0] = cbi->cbEndS[1] = cbi->cbEndS[2] = 0;
  cbi->cbEndSMax = 0;
 
  /* early exit if no short blocks */
  if (cbStartS >= 12) 
    return CLZ(gbMask) - 1;
  
  /* short blocks */
  cbMax[2] = cbMax[1] = cbMax[0] = cbStartS;
  for (cb = cbStartS; cb < cbEndS; cb++) {
 
    nSamps = fh->sfBand->s[cb + 1] - fh->sfBand->s[cb];
    for (w = 0; w < 3; w++) {
      nonZero =  0;
      gainI = 210 - globalGain + 8*sis->subBlockGain[w] + sfactMultiplier*(sfis->s[cb][w]);
 
      nonZero |= DequantBlock(sampleBuf + i + nSamps*w, workBuf + nSamps*w, nSamps, gainI);
 
      /* update highest non-zero critical band */
      if (nonZero)
        cbMax[w] = cb;
      gbMask |= nonZero;
    }
 
    /* reorder blocks */
    buf = (ARRAY3 *)(sampleBuf + i);
    i += 3*nSamps;
    for (j = 0; j < nSamps; j++) {
      buf[j][0] = workBuf[0*nSamps + j];
      buf[j][1] = workBuf[1*nSamps + j];
      buf[j][2] = workBuf[2*nSamps + j];
    }
 
    ASSERT(3*nSamps <= MAX_REORDER_SAMPS);
 
    if (i >= *nonZeroBound) 
      break;
  }
 
  /* i = last non-zero INPUT sample processed, which corresponds to highest possible non-zero 
   *     OUTPUT sample (after reorder)
   * however, the original nzb is no longer necessarily true
   *   for each cb, buf[][] is updated with 3*nSamps samples (i increases 3*nSamps each time)
   *   (buf[j + 1][0] = 3 (input) samples ahead of buf[j][0])
     * so update nonZeroBound to i
   */
  *nonZeroBound = i;
 
  ASSERT(*nonZeroBound <= MAX_NSAMP);
 
  cbi->cbType = (sis->mixedBlock ? 2 : 1);  /* 2 = mixed short/long, 1 = short only */
 
  cbi->cbEndS[0] = cbMax[0];
  cbi->cbEndS[1] = cbMax[1];
  cbi->cbEndS[2] = cbMax[2];
 
  cbi->cbEndSMax = cbMax[0];
  cbi->cbEndSMax = MAX(cbi->cbEndSMax, cbMax[1]);
  cbi->cbEndSMax = MAX(cbi->cbEndSMax, cbMax[2]);
 
  return CLZ(gbMask) - 1;
}