scalfact.c

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/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
 * June 2003
 *
 * scalfact.c - scalefactor unpacking functions
 **************************************************************************************/
 
#include "coder.h"
 
/* scale factor lengths (num bits) */
static const char SFLenTab[16][2] = {
  {0, 0},    {0, 1},
  {0, 2},    {0, 3},
  {3, 0},    {1, 1},
  {1, 2},    {1, 3},
  {2, 1},    {2, 2},
  {2, 3},    {3, 1},
  {3, 2},    {3, 3},
  {4, 2},    {4, 3},
};
 
/**************************************************************************************
 * Function:    UnpackSFMPEG1
 *
 * Description: unpack MPEG 1 scalefactors from bitstream
 *
 * Inputs:      BitStreamInfo, SideInfoSub, ScaleFactorInfoSub structs for this
 *                granule/channel
 *              vector of scfsi flags from side info, length = 4 (MAX_SCFBD)
 *              index of current granule
 *              ScaleFactorInfoSub from granule 0 (for granule 1, if scfsi[i] is set, 
 *                then we just replicate the scale factors from granule 0 in the
 *                i'th set of scalefactor bands)
 *
 * Outputs:     updated BitStreamInfo struct
 *              scalefactors in sfis (short and/or long arrays, as appropriate)
 *
 * Return:      none
 *
 * Notes:       set order of short blocks to s[band][window] instead of s[window][band]
 *                so that we index through consectutive memory locations when unpacking 
 *                (make sure dequantizer follows same convention)
 *              Illegal Intensity Position = 7 (always) for MPEG1 scale factors
 **************************************************************************************/
static void UnpackSFMPEG1(BitStreamInfo *bsi, SideInfoSub *sis, ScaleFactorInfoSub *sfis, int *scfsi, int gr, ScaleFactorInfoSub *sfisGr0)
{
  int sfb;
  int slen0, slen1;
  
  /* these can be 0, so make sure GetBits(bsi, 0) returns 0 (no >> 32 or anything) */
  slen0 = (int)SFLenTab[sis->sfCompress][0];
  slen1 = (int)SFLenTab[sis->sfCompress][1];
  
  if (sis->blockType == 2) {
    /* short block, type 2 (implies winSwitchFlag == 1) */
    if (sis->mixedBlock) {          
      /* do long block portion */
      for (sfb = 0; sfb < 8; sfb++)
        sfis->l[sfb] =    (char)GetBits(bsi, slen0);
      sfb = 3;
    } else {
      /* all short blocks */
      sfb = 0;
    }
 
    for (      ; sfb < 6; sfb++) {
      sfis->s[sfb][0] = (char)GetBits(bsi, slen0);
      sfis->s[sfb][1] = (char)GetBits(bsi, slen0);
      sfis->s[sfb][2] = (char)GetBits(bsi, slen0);
    }
 
    for (      ; sfb < 12; sfb++) {
      sfis->s[sfb][0] = (char)GetBits(bsi, slen1);
      sfis->s[sfb][1] = (char)GetBits(bsi, slen1);
      sfis->s[sfb][2] = (char)GetBits(bsi, slen1);
    }
 
    /* last sf band not transmitted */
    sfis->s[12][0] = sfis->s[12][1] = sfis->s[12][2] = 0;
  } else {
    /* long blocks, type 0, 1, or 3 */
    if(gr == 0) {
      /* first granule */
      for (sfb = 0;  sfb < 11; sfb++) 
        sfis->l[sfb] = (char)GetBits(bsi, slen0);
      for (sfb = 11; sfb < 21; sfb++) 
        sfis->l[sfb] = (char)GetBits(bsi, slen1);
      return;
    } else {
      /* second granule
       * scfsi: 0 = different scalefactors for each granule, 1 = copy sf's from granule 0 into granule 1 
       * for block type == 2, scfsi is always 0
       */
      sfb = 0;
      if(scfsi[0])  for(  ; sfb < 6 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
      else          for(  ; sfb < 6 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen0);
      if(scfsi[1])  for(  ; sfb <11 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
      else          for(  ; sfb <11 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen0);
      if(scfsi[2])  for(  ; sfb <16 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
      else          for(  ; sfb <16 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen1);
      if(scfsi[3])  for(  ; sfb <21 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
      else          for(  ; sfb <21 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen1);
    }
    /* last sf band not transmitted */
    sfis->l[21] = 0;
    sfis->l[22] = 0;
  }
}
 
/* NRTab[size + 3*is_right][block type][partition]
 *   block type index: 0 = (bt0,bt1,bt3), 1 = bt2 non-mixed, 2 = bt2 mixed
 *   partition: scale factor groups (sfb1 through sfb4)
 * for block type = 2 (mixed or non-mixed) / by 3 is rolled into this table
 *   (for 3 short blocks per long block)
 * see 2.4.3.2 in MPEG 2 (low sample rate) spec
 * stuff rolled into this table:
 *   NRTab[x][1][y]   --> (NRTab[x][1][y])   / 3
 *   NRTab[x][2][>=1] --> (NRTab[x][2][>=1]) / 3  (first partition is long block)
 */
static const char NRTab[6][3][4] = {
  /* non-intensity stereo */
  { {6, 5, 5, 5},   
    {3, 3, 3, 3}, /* includes / 3 */  
    {6, 3, 3, 3},   /* includes / 3 except for first entry */
  },
  { {6, 5, 7, 3}, 
    {3, 3, 4, 2},
    {6, 3, 4, 2},
  },
  { {11, 10, 0, 0},
    {6, 6, 0, 0},
    {6, 3, 6, 0},  /* spec = [15,18,0,0], but 15 = 6L + 9S, so move 9/3=3 into col 1, 18/3=6 into col 2 and adj. slen[1,2] below */
  },
  /* intensity stereo, right chan */
  { {7, 7, 7, 0},
    {4, 4, 4, 0},
    {6, 5, 4, 0},
  },
  { {6, 6, 6, 3}, 
    {4, 3, 3, 2},
    {6, 4, 3, 2},
  },
  { {8, 8, 5, 0},
    {5, 4, 3, 0},
    {6, 6, 3, 0},
  }
};
 
/**************************************************************************************
 * Function:    UnpackSFMPEG2
 *
 * Description: unpack MPEG 2 scalefactors from bitstream
 *
 * Inputs:      BitStreamInfo, SideInfoSub, ScaleFactorInfoSub structs for this
 *                granule/channel
 *              index of current granule and channel
 *              ScaleFactorInfoSub from this granule 
 *              modeExt field from frame header, to tell whether intensity stereo is on
 *              ScaleFactorJS struct for storing IIP info used in Dequant()
 *
 * Outputs:     updated BitStreamInfo struct
 *              scalefactors in sfis (short and/or long arrays, as appropriate)
 *              updated intensityScale and preFlag flags
 *
 * Return:      none
 *
 * Notes:       Illegal Intensity Position = (2^slen) - 1 for MPEG2 scale factors
 *
 * TODO:        optimize the / and % stuff (only do one divide, get modulo x 
 *                with (x / m) * m, etc.)
 **************************************************************************************/
static void UnpackSFMPEG2(BitStreamInfo *bsi, SideInfoSub *sis, ScaleFactorInfoSub *sfis, int gr, int ch, int modeExt, ScaleFactorJS *sfjs)
{
 
  int i, sfb, sfcIdx, btIdx, nrIdx;
  int slen[4], nr[4];
  int sfCompress, preFlag, intensityScale;
  
  sfCompress = sis->sfCompress;
  preFlag = 0;
  intensityScale = 0;
 
  /* stereo mode bits (1 = on): bit 1 = mid-side on/off, bit 0 = intensity on/off */
  if (! ((modeExt & 0x01) && (ch == 1)) ) {
    /* in other words: if ((modeExt & 0x01) == 0 || ch == 0) */
    if (sfCompress < 400) {
      /* max slen = floor[(399/16) / 5] = 4 */
      slen[0] = (sfCompress >> 4) / 5;
      slen[1]= (sfCompress >> 4) % 5;
      slen[2]= (sfCompress & 0x0f) >> 2;
      slen[3]= (sfCompress & 0x03);
      sfcIdx = 0;
    } else if (sfCompress < 500) {
      /* max slen = floor[(99/4) / 5] = 4 */
      sfCompress -= 400;
      slen[0] = (sfCompress >> 2) / 5;
      slen[1]= (sfCompress >> 2) % 5;
      slen[2]= (sfCompress & 0x03);
      slen[3]= 0;
      sfcIdx = 1;
    } else {
      /* max slen = floor[11/3] = 3 (sfCompress = 9 bits in MPEG2) */
      sfCompress -= 500;
      slen[0] = sfCompress / 3;
      slen[1] = sfCompress % 3;
      slen[2] = slen[3] = 0;
      if (sis->mixedBlock) {
        /* adjust for long/short mix logic (see comment above in NRTab[] definition) */
        slen[2] = slen[1];  
        slen[1] = slen[0];
      }  
      preFlag = 1;
      sfcIdx = 2;
    }
  } else {    
    /* intensity stereo ch = 1 (right) */
    intensityScale = sfCompress & 0x01;
    sfCompress >>= 1;
    if (sfCompress < 180) {
      /* max slen = floor[35/6] = 5 (from mod 36) */
      slen[0] = (sfCompress / 36);
      slen[1] = (sfCompress % 36) / 6;
      slen[2] = (sfCompress % 36) % 6;
      slen[3] = 0;
      sfcIdx = 3;
    } else if (sfCompress < 244) {
      /* max slen = floor[63/16] = 3 */
      sfCompress -= 180;
      slen[0] = (sfCompress & 0x3f) >> 4;
      slen[1] = (sfCompress & 0x0f) >> 2;
      slen[2] = (sfCompress & 0x03);
      slen[3] = 0;
      sfcIdx = 4;
    } else {
      /* max slen = floor[11/3] = 3 (max sfCompress >> 1 = 511/2 = 255) */
      sfCompress -= 244;
      slen[0] = (sfCompress / 3);
      slen[1] = (sfCompress % 3);
      slen[2] = slen[3] = 0;
      sfcIdx = 5;
    }
  }
  
  /* set index based on block type: (0,1,3) --> 0, (2 non-mixed) --> 1, (2 mixed) ---> 2 */
  btIdx = 0;
  if (sis->blockType == 2) 
    btIdx = (sis->mixedBlock ? 2 : 1);
  for (i = 0; i < 4; i++)
    nr[i] = (int)NRTab[sfcIdx][btIdx][i];
 
  /* save intensity stereo scale factor info */
  if( (modeExt & 0x01) && (ch == 1) ) {
    for (i = 0; i < 4; i++) {
      sfjs->slen[i] = slen[i];
      sfjs->nr[i] = nr[i];
    }
    sfjs->intensityScale = intensityScale;
  }
  sis->preFlag = preFlag;
 
  /* short blocks */
  if(sis->blockType == 2) {
    if(sis->mixedBlock) {
      /* do long block portion */
      for (sfb=0; sfb < 6; sfb++) {
        sfis->l[sfb] = (char)GetBits(bsi, slen[0]);
      }
      sfb = 3;  /* start sfb for short */
      nrIdx = 1;
    } else {      
      /* all short blocks, so start nr, sfb at 0 */
      sfb = 0;
      nrIdx = 0;
    }
 
    /* remaining short blocks, sfb just keeps incrementing */
    for (    ; nrIdx <= 3; nrIdx++) {
      for (i=0; i < nr[nrIdx]; i++, sfb++) {
        sfis->s[sfb][0] = (char)GetBits(bsi, slen[nrIdx]);
        sfis->s[sfb][1] = (char)GetBits(bsi, slen[nrIdx]);
        sfis->s[sfb][2] = (char)GetBits(bsi, slen[nrIdx]);
      }
    }
    /* last sf band not transmitted */
    sfis->s[12][0] = sfis->s[12][1] = sfis->s[12][2] = 0;
  } else {
    /* long blocks */
    sfb = 0;
    for (nrIdx = 0; nrIdx <= 3; nrIdx++) {
      for(i=0; i < nr[nrIdx]; i++, sfb++) {
        sfis->l[sfb] = (char)GetBits(bsi, slen[nrIdx]);
      }
    }
    /* last sf band not transmitted */
    sfis->l[21] = sfis->l[22] = 0;
 
  }
}
 
/**************************************************************************************
 * Function:    UnpackScaleFactors
 *
 * Description: parse the fields of the MP3 scale factor data section
 *
 * Inputs:      MP3DecInfo structure filled by UnpackFrameHeader() and UnpackSideInfo()
 *              buffer pointing to the MP3 scale factor data
 *              pointer to bit offset (0-7) indicating starting bit in buf[0]
 *              number of bits available in data buffer
 *              index of current granule and channel
 *
 * Outputs:     updated platform-specific ScaleFactorInfo struct
 *              updated bitOffset
 *
 * Return:      length (in bytes) of scale factor data, -1 if null input pointers
 **************************************************************************************/
int UnpackScaleFactors(MP3DecInfo *mp3DecInfo, unsigned char *buf, int *bitOffset, int bitsAvail, int gr, int ch)
{
  int bitsUsed;
  unsigned char *startBuf;
  BitStreamInfo bitStreamInfo, *bsi;
  FrameHeader *fh;
  SideInfo *si;
  ScaleFactorInfo *sfi;
 
  /* validate pointers */
  if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->ScaleFactorInfoPS)
    return -1;
  fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
  si = ((SideInfo *)(mp3DecInfo->SideInfoPS));
  sfi = ((ScaleFactorInfo *)(mp3DecInfo->ScaleFactorInfoPS));
 
  /* init GetBits reader */
  startBuf = buf;
  bsi = &bitStreamInfo;
  SetBitstreamPointer(bsi, (bitsAvail + *bitOffset + 7) / 8, buf);
  if (*bitOffset)
    GetBits(bsi, *bitOffset);
 
  if (fh->ver == MPEG1) 
    UnpackSFMPEG1(bsi, &si->sis[gr][ch], &sfi->sfis[gr][ch], si->scfsi[ch], gr, &sfi->sfis[0][ch]);
  else 
    UnpackSFMPEG2(bsi, &si->sis[gr][ch], &sfi->sfis[gr][ch], gr, ch, fh->modeExt, &sfi->sfjs);
 
  mp3DecInfo->part23Length[gr][ch] = si->sis[gr][ch].part23Length;
 
  bitsUsed = CalcBitsUsed(bsi, buf, *bitOffset);
  buf += (bitsUsed + *bitOffset) >> 3;
  *bitOffset = (bitsUsed + *bitOffset) & 0x07;
 
  return (int)(buf - startBuf);
}