//------------------------------------------------------------------------
// Decoding a DCT stream (JPEG image)
// This code has been taken from Xpdf,
// Copyright 1996-2002 Glyph & Cog, LLC
//------------------------------------------------------------------------
/*

    This file is part of the extensible drawing editor Ipe.
    Copyright (C) 1993-2013  Otfried Cheong

    Ipe is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    As a special exception, you have permission to link Ipe with the
    CGAL library and distribute executables, as long as you follow the
    requirements of the Gnu General Public License in regard to all of
    the software in the executable aside from CGAL.

    Ipe is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
    License for more details.

    You should have received a copy of the GNU General Public License
    along with Ipe; if not, you can find it at
    "http://www.gnu.org/copyleft/gpl.html", or write to the Free
    Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#include "ipebase.h"

using namespace ipe;

// --------------------------------------------------------------------

// DCT component info
struct DCTCompInfo {
  int id;			// component ID
  int hSample, vSample;		// horiz/vert sampling resolutions
  int quantTable;		// quantization table number
  int prevDC;			// DC coefficient accumulator
};

struct DCTScanInfo {
  bool comp[4];	                // comp[i] is set if component i is
				//   included in this scan
  int numComps;			// number of components in the scan
  int dcHuffTable[4];		// DC Huffman table numbers
  int acHuffTable[4];		// AC Huffman table numbers
  int firstCoeff, lastCoeff;	// first and last DCT coefficient
  int ah, al;			// successive approximation parameters
};

// DCT Huffman decoding table
struct DCTHuffTable {
  uchar firstSym[17];		// first symbol for this bit length
  ushort firstCode[17];	        // first code for this bit length
  ushort numCodes[17];		// number of codes of this bit length
  uchar sym[256];		// symbols
};

// --------------------------------------------------------------------

class DCTStream {
public:

  DCTStream(DataSource &source);
  ~DCTStream();
  void reset();
  int getChar();

private:
  DataSource &iSource;

  bool progressive;		// set if in progressive mode
  bool interleaved;		// set if in interleaved mode
  int width, height;		// image size
  int mcuWidth, mcuHeight;	// size of min coding unit, in data units
  int bufWidth, bufHeight;	// frameBuf size
  DCTCompInfo compInfo[4];	// info for each component
  DCTScanInfo scanInfo;		// info for the current scan
  int numComps;			// number of components in image
  int colorXform;		// need YCbCr-to-RGB transform?
  bool gotAdobeMarker;		// set if APP14 Adobe marker was present
  int restartInterval;		// restart interval, in MCUs
  uchar quantTables[4][64];	// quantization tables
  int numQuantTables;		// number of quantization tables
  DCTHuffTable dcHuffTables[4];	// DC Huffman tables
  DCTHuffTable acHuffTables[4];	// AC Huffman tables
  int numDCHuffTables;		// number of DC Huffman tables
  int numACHuffTables;		// number of AC Huffman tables
  uchar *rowBuf[4][32];		// buffer for one MCU (non-progressive mode)
  int *frameBuf[4];		// buffer for frame (progressive mode)
  int comp, x, y, dy;		// current position within image/MCU
  int restartCtr;		// MCUs left until restart
  int restartMarker;		// next restart marker
  int eobRun;			// number of EOBs left in the current run
  int inputBuf;			// input buffer for variable length codes
  int inputBits;		// number of valid bits in input buffer

  void restart();
  bool readMCURow();
  void readScan();
  bool readDataUnit(DCTHuffTable *dcHuffTable,
		    DCTHuffTable *acHuffTable,
		    int *prevDC, int data[64]);
  bool readProgressiveDataUnit(DCTHuffTable *dcHuffTable,
			       DCTHuffTable *acHuffTable,
			       int *prevDC, int data[64]);
  void decodeImage();
  void transformDataUnit(uchar *quantTable,
			 int dataIn[64], uchar dataOut[64]);
  int readHuffSym(DCTHuffTable *table);
  int readAmp(int size);
  int readBit();
  bool readHeader();
  bool readBaselineSOF();
  bool readProgressiveSOF();
  bool readScanInfo();
  bool readQuantTables();
  bool readHuffmanTables();
  bool readRestartInterval();
  bool readAdobeMarker();
  bool readTrailer();
  int readMarker();
  int read16();
};

// --------------------------------------------------------------------

// IDCT constants (20.12 fixed point format)
#define dctCos1    4017		// cos(pi/16)
#define dctSin1     799		// sin(pi/16)
#define dctCos3    3406		// cos(3*pi/16)
#define dctSin3    2276		// sin(3*pi/16)
#define dctCos6    1567		// cos(6*pi/16)
#define dctSin6    3784		// sin(6*pi/16)
#define dctSqrt2   5793		// sqrt(2)
#define dctSqrt1d2 2896		// sqrt(2) / 2

// color conversion parameters (16.16 fixed point format)
#define dctCrToR   91881	//  1.4020
#define dctCbToG  -22553	// -0.3441363
#define dctCrToG  -46802	// -0.71413636
#define dctCbToB  116130	//  1.772

// clip [-256,511] --> [0,255]
#define dctClipOffset 256
static uchar dctClip[768];
static int dctClipInit = 0;

// zig zag decode map
static int dctZigZag[64] = {
   0,
   1,  8,
  16,  9,  2,
   3, 10, 17, 24,
  32, 25, 18, 11, 4,
   5, 12, 19, 26, 33, 40,
  48, 41, 34, 27, 20, 13,  6,
   7, 14, 21, 28, 35, 42, 49, 56,
  57, 50, 43, 36, 29, 22, 15,
  23, 30, 37, 44, 51, 58,
  59, 52, 45, 38, 31,
  39, 46, 53, 60,
  61, 54, 47,
  55, 62,
  63
};

// --------------------------------------------------------------------

DCTStream::DCTStream(DataSource &source)
  : iSource(source)
{
  int i, j;

  progressive = interleaved = false;
  width = height = 0;
  mcuWidth = mcuHeight = 0;
  numComps = 0;
  comp = 0;
  x = y = dy = 0;
  for (i = 0; i < 4; ++i) {
    for (j = 0; j < 32; ++j) {
      rowBuf[i][j] = 0;
    }
    frameBuf[i] = 0;
  }

  if (!dctClipInit) {
    for (i = -256; i < 0; ++i)
      dctClip[dctClipOffset + i] = 0;
    for (i = 0; i < 256; ++i)
      dctClip[dctClipOffset + i] = uchar(i);
    for (i = 256; i < 512; ++i)
      dctClip[dctClipOffset + i] = 255;
    dctClipInit = 1;
  }
}

DCTStream::~DCTStream()
{
  int i, j;
  if (progressive || !interleaved) {
    for (i = 0; i < numComps; ++i) {
      delete [] frameBuf[i];
    }
  } else {
    for (i = 0; i < numComps; ++i) {
      for (j = 0; j < mcuHeight; ++j) {
	delete [] rowBuf[i][j];
      }
    }
  }
}

void DCTStream::reset()
{
  int minHSample, minVSample;
  int i, j;

  progressive = interleaved = false;
  width = height = 0;
  numComps = 0;
  numQuantTables = 0;
  numDCHuffTables = 0;
  numACHuffTables = 0;
  colorXform = 0;
  gotAdobeMarker = false;
  restartInterval = 0;

  if (!readHeader()) {
    y = height;
    return;
  }

  // compute MCU size
  mcuWidth = minHSample = compInfo[0].hSample;
  mcuHeight = minVSample = compInfo[0].vSample;
  for (i = 1; i < numComps; ++i) {
    if (compInfo[i].hSample < minHSample)
      minHSample = compInfo[i].hSample;
    if (compInfo[i].vSample < minVSample)
      minVSample = compInfo[i].vSample;
    if (compInfo[i].hSample > mcuWidth)
      mcuWidth = compInfo[i].hSample;
    if (compInfo[i].vSample > mcuHeight)
      mcuHeight = compInfo[i].vSample;
  }
  for (i = 0; i < numComps; ++i) {
    compInfo[i].hSample /= minHSample;
    compInfo[i].vSample /= minVSample;
  }
  mcuWidth = (mcuWidth / minHSample) * 8;
  mcuHeight = (mcuHeight / minVSample) * 8;

  // figure out color transform
  if (!gotAdobeMarker && numComps == 3) {
    if (compInfo[0].id == 1 && compInfo[1].id == 2 && compInfo[2].id == 3) {
      colorXform = 1;
    }
  }

  if (progressive || !interleaved) {

    // allocate a buffer for the whole image
    bufWidth = ((width + mcuWidth - 1) / mcuWidth) * mcuWidth;
    bufHeight = ((height + mcuHeight - 1) / mcuHeight) * mcuHeight;
    for (i = 0; i < numComps; ++i) {
      frameBuf[i] = new int[bufWidth * bufHeight];
      memset(frameBuf[i], 0, bufWidth * bufHeight * sizeof(int));
    }

    // read the image data
    do {
      restartMarker = 0xd0;
      restart();
      readScan();
    } while (readHeader());

    // decode
    decodeImage();

    // initialize counters
    comp = 0;
    x = 0;
    y = 0;

  } else {

    // allocate a buffer for one row of MCUs
    bufWidth = ((width + mcuWidth - 1) / mcuWidth) * mcuWidth;
    for (i = 0; i < numComps; ++i) {
      for (j = 0; j < mcuHeight; ++j) {
	rowBuf[i][j] = new uchar[bufWidth];
      }
    }

    // initialize counters
    comp = 0;
    x = 0;
    y = 0;
    dy = mcuHeight;

    restartMarker = 0xd0;
    restart();
  }
}

int DCTStream::getChar()
{
  int c;

  if (y >= height) {
    return EOF;
  }
  if (progressive || !interleaved) {
    c = frameBuf[comp][y * bufWidth + x];
    if (++comp == numComps) {
      comp = 0;
      if (++x == width) {
	x = 0;
	++y;
      }
    }
  } else {
    if (dy >= mcuHeight) {
      if (!readMCURow()) {
	y = height;
	return EOF;
      }
      comp = 0;
      x = 0;
      dy = 0;
    }
    c = rowBuf[comp][dy][x];
    if (++comp == numComps) {
      comp = 0;
      if (++x == width) {
	x = 0;
	++y;
	++dy;
	if (y == height) {
	  readTrailer();
	}
      }
    }
  }
  return c;
}

void DCTStream::restart()
{
  int i;

  inputBits = 0;
  restartCtr = restartInterval;
  for (i = 0; i < numComps; ++i) {
    compInfo[i].prevDC = 0;
  }
  eobRun = 0;
}

// Read one row of MCUs from a sequential JPEG stream.
bool DCTStream::readMCURow()
{
  int data1[64];
  uchar data2[64];
  uchar *p1, *p2;
  int pY, pCb, pCr, pR, pG, pB;
  int h, v, horiz, vert, hSub, vSub;
  int x1, x2, y2, x3, y3, x4, y4, x5, y5, cc, i;
  int c;

  for (x1 = 0; x1 < width; x1 += mcuWidth) {

    // deal with restart marker
    if (restartInterval > 0 && restartCtr == 0) {
      c = readMarker();
      if (c != restartMarker) {
	ipeDebug("Bad DCT data: incorrect restart marker");
	return false;
      }
      if (++restartMarker == 0xd8)
	restartMarker = 0xd0;
      restart();
    }

    // read one MCU
    for (cc = 0; cc < numComps; ++cc) {
      h = compInfo[cc].hSample;
      v = compInfo[cc].vSample;
      horiz = mcuWidth / h;
      vert = mcuHeight / v;
      hSub = horiz / 8;
      vSub = vert / 8;
      for (y2 = 0; y2 < mcuHeight; y2 += vert) {
	for (x2 = 0; x2 < mcuWidth; x2 += horiz) {
	  if (!readDataUnit(&dcHuffTables[scanInfo.dcHuffTable[cc]],
			    &acHuffTables[scanInfo.acHuffTable[cc]],
			    &compInfo[cc].prevDC,
			    data1)) {
	    return false;
	  }
	  transformDataUnit(quantTables[compInfo[cc].quantTable],
			    data1, data2);
	  if (hSub == 1 && vSub == 1) {
	    for (y3 = 0, i = 0; y3 < 8; ++y3, i += 8) {
	      p1 = &rowBuf[cc][y2+y3][x1+x2];
	      p1[0] = data2[i];
	      p1[1] = data2[i+1];
	      p1[2] = data2[i+2];
	      p1[3] = data2[i+3];
	      p1[4] = data2[i+4];
	      p1[5] = data2[i+5];
	      p1[6] = data2[i+6];
	      p1[7] = data2[i+7];
	    }
	  } else if (hSub == 2 && vSub == 2) {
	    for (y3 = 0, i = 0; y3 < 16; y3 += 2, i += 8) {
	      p1 = &rowBuf[cc][y2+y3][x1+x2];
	      p2 = &rowBuf[cc][y2+y3+1][x1+x2];
	      p1[0] = p1[1] = p2[0] = p2[1] = data2[i];
	      p1[2] = p1[3] = p2[2] = p2[3] = data2[i+1];
	      p1[4] = p1[5] = p2[4] = p2[5] = data2[i+2];
	      p1[6] = p1[7] = p2[6] = p2[7] = data2[i+3];
	      p1[8] = p1[9] = p2[8] = p2[9] = data2[i+4];
	      p1[10] = p1[11] = p2[10] = p2[11] = data2[i+5];
	      p1[12] = p1[13] = p2[12] = p2[13] = data2[i+6];
	      p1[14] = p1[15] = p2[14] = p2[15] = data2[i+7];
	    }
	  } else {
	    i = 0;
	    for (y3 = 0, y4 = 0; y3 < 8; ++y3, y4 += vSub) {
	      for (x3 = 0, x4 = 0; x3 < 8; ++x3, x4 += hSub) {
		for (y5 = 0; y5 < vSub; ++y5)
		  for (x5 = 0; x5 < hSub; ++x5)
		    rowBuf[cc][y2+y4+y5][x1+x2+x4+x5] = data2[i];
		++i;
	      }
	    }
	  }
	}
      }
    }
    --restartCtr;

    // color space conversion
    if (colorXform) {
      // convert YCbCr to RGB
      if (numComps == 3) {
	for (y2 = 0; y2 < mcuHeight; ++y2) {
	  for (x2 = 0; x2 < mcuWidth; ++x2) {
	    pY = rowBuf[0][y2][x1+x2];
	    pCb = rowBuf[1][y2][x1+x2] - 128;
	    pCr = rowBuf[2][y2][x1+x2] - 128;
	    pR = ((pY << 16) + dctCrToR * pCr + 32768) >> 16;
	    rowBuf[0][y2][x1+x2] = dctClip[dctClipOffset + pR];
	    pG = ((pY << 16) + dctCbToG * pCb + dctCrToG * pCr + 32768) >> 16;
	    rowBuf[1][y2][x1+x2] = dctClip[dctClipOffset + pG];
	    pB = ((pY << 16) + dctCbToB * pCb + 32768) >> 16;
	    rowBuf[2][y2][x1+x2] = dctClip[dctClipOffset + pB];
	  }
	}
      // convert YCbCrK to CMYK (K is passed through unchanged)
      } else if (numComps == 4) {
	for (y2 = 0; y2 < mcuHeight; ++y2) {
	  for (x2 = 0; x2 < mcuWidth; ++x2) {
	    pY = rowBuf[0][y2][x1+x2];
	    pCb = rowBuf[1][y2][x1+x2] - 128;
	    pCr = rowBuf[2][y2][x1+x2] - 128;
	    pR = ((pY << 16) + dctCrToR * pCr + 32768) >> 16;
	    rowBuf[0][y2][x1+x2] = uchar(255 - dctClip[dctClipOffset + pR]);
	    pG = ((pY << 16) + dctCbToG * pCb + dctCrToG * pCr + 32768) >> 16;
	    rowBuf[1][y2][x1+x2] = uchar(255 - dctClip[dctClipOffset + pG]);
	    pB = ((pY << 16) + dctCbToB * pCb + 32768) >> 16;
	    rowBuf[2][y2][x1+x2] = uchar(255 - dctClip[dctClipOffset + pB]);
	  }
	}
      }
    }
  }
  return true;
}

// Read one scan from a progressive or non-interleaved JPEG stream.
void DCTStream::readScan()
{
  int data[64];
  int x1, y1, dy1, x2, y2, y3, cc, i;
  int h, v, horiz, vert, vSub;
  int *p1;
  int c;

  if (scanInfo.numComps == 1) {
    for (cc = 0; cc < numComps; ++cc) {
      if (scanInfo.comp[cc]) {
	break;
      }
    }
    dy1 = mcuHeight / compInfo[cc].vSample;
  } else {
    dy1 = mcuHeight;
  }

  for (y1 = 0; y1 < bufHeight; y1 += dy1) {
    for (x1 = 0; x1 < bufWidth; x1 += mcuWidth) {

      // deal with restart marker
      if (restartInterval > 0 && restartCtr == 0) {
	c = readMarker();
	if (c != restartMarker) {
	  ipeDebug("Bad DCT data: incorrect restart marker");
	  return;
	}
	if (++restartMarker == 0xd8) {
	  restartMarker = 0xd0;
	}
	restart();
      }

      // read one MCU
      for (cc = 0; cc < numComps; ++cc) {
	if (!scanInfo.comp[cc]) {
	  continue;
	}

	h = compInfo[cc].hSample;
	v = compInfo[cc].vSample;
	horiz = mcuWidth / h;
	vert = mcuHeight / v;
	// hSub = horiz / 8;
	vSub = vert / 8;
	for (y2 = 0; y2 < dy1; y2 += vert) {
	  for (x2 = 0; x2 < mcuWidth; x2 += horiz) {

	    // pull out the current values
	    p1 = &frameBuf[cc][(y1+y2) * bufWidth + (x1+x2)];
	    for (y3 = 0, i = 0; y3 < 8; ++y3, i += 8) {
	      data[i] = p1[0];
	      data[i+1] = p1[1];
	      data[i+2] = p1[2];
	      data[i+3] = p1[3];
	      data[i+4] = p1[4];
	      data[i+5] = p1[5];
	      data[i+6] = p1[6];
	      data[i+7] = p1[7];
	      p1 += bufWidth * vSub;
	    }

	    // read one data unit
	    if (progressive) {
	      if (!readProgressiveDataUnit(
		       &dcHuffTables[scanInfo.dcHuffTable[cc]],
		       &acHuffTables[scanInfo.acHuffTable[cc]],
		       &compInfo[cc].prevDC,
		       data)) {
		return;
	      }
	    } else {
	      if (!readDataUnit(&dcHuffTables[scanInfo.dcHuffTable[cc]],
				&acHuffTables[scanInfo.acHuffTable[cc]],
				&compInfo[cc].prevDC,
				data)) {
		return;
	      }
	    }

	    // add the data unit into frameBuf
	    p1 = &frameBuf[cc][(y1+y2) * bufWidth + (x1+x2)];
	    for (y3 = 0, i = 0; y3 < 8; ++y3, i += 8) {
	      p1[0] = data[i];
	      p1[1] = data[i+1];
	      p1[2] = data[i+2];
	      p1[3] = data[i+3];
	      p1[4] = data[i+4];
	      p1[5] = data[i+5];
	      p1[6] = data[i+6];
	      p1[7] = data[i+7];
	      p1 += bufWidth * vSub;
	    }
	  }
	}
      }
      --restartCtr;
    }
  }
}

// Read one data unit from a sequential JPEG stream.
bool DCTStream::readDataUnit(DCTHuffTable *dcHuffTable,
			     DCTHuffTable *acHuffTable,
			     int *prevDC, int data[64])
{
  int run, size, amp;
  int c;
  int i, j;

  if ((size = readHuffSym(dcHuffTable)) == 9999) {
    return false;
  }
  if (size > 0) {
    if ((amp = readAmp(size)) == 9999) {
      return false;
    }
  } else {
    amp = 0;
  }
  data[0] = *prevDC += amp;
  for (i = 1; i < 64; ++i) {
    data[i] = 0;
  }
  i = 1;
  while (i < 64) {
    run = 0;
    while ((c = readHuffSym(acHuffTable)) == 0xf0 && run < 0x30) {
      run += 0x10;
    }
    if (c == 9999) {
      return false;
    }
    if (c == 0x00) {
      break;
    } else {
      run += (c >> 4) & 0x0f;
      size = c & 0x0f;
      amp = readAmp(size);
      if (amp == 9999) {
	return false;
      }
      i += run;
      j = dctZigZag[i++];
      data[j] = amp;
    }
  }
  return true;
}

// Read one data unit from a sequential JPEG stream.
bool DCTStream::readProgressiveDataUnit(DCTHuffTable *dcHuffTable,
					DCTHuffTable *acHuffTable,
					int *prevDC, int data[64])
{
  int run, size, amp, bit, c;
  int i, j, k;

  // get the DC coefficient
  i = scanInfo.firstCoeff;
  if (i == 0) {
    if (scanInfo.ah == 0) {
      if ((size = readHuffSym(dcHuffTable)) == 9999) {
	return false;
      }
      if (size > 0) {
	if ((amp = readAmp(size)) == 9999) {
	  return false;
	}
      } else {
	amp = 0;
      }
      data[0] += (*prevDC += amp) << scanInfo.al;
    } else {
      if ((bit = readBit()) == 9999) {
	return false;
      }
      data[0] += bit << scanInfo.al;
    }
    ++i;
  }
  if (scanInfo.lastCoeff == 0) {
    return true;
  }

  // check for an EOB run
  if (eobRun > 0) {
    while (i <= scanInfo.lastCoeff) {
      j = dctZigZag[i++];
      if (data[j] != 0) {
	if ((bit = readBit()) == EOF) {
	  return false;
	}
	if (bit) {
	  data[j] += 1 << scanInfo.al;
	}
      }
    }
    --eobRun;
    return true;
  }

  // read the AC coefficients
  while (i <= scanInfo.lastCoeff) {
    if ((c = readHuffSym(acHuffTable)) == 9999) {
      return false;
    }

    // ZRL
    if (c == 0xf0) {
      k = 0;
      while (k < 16) {
	j = dctZigZag[i++];
	if (data[j] == 0) {
	  ++k;
	} else {
	  if ((bit = readBit()) == EOF) {
	    return false;
	  }
	  if (bit) {
	    data[j] += 1 << scanInfo.al;
	  }
	}
      }

    // EOB run
    } else if ((c & 0x0f) == 0x00) {
      j = c >> 4;
      eobRun = 0;
      for (k = 0; k < j; ++k) {
	if ((bit = readBit()) == EOF) {
	  return 9999;
	}
	eobRun = (eobRun << 1) | bit;
      }
      eobRun += 1 << j;
      while (i <= scanInfo.lastCoeff) {
	j = dctZigZag[i++];
	if (data[j] != 0) {
	  if ((bit = readBit()) == EOF) {
	    return false;
	  }
	  if (bit) {
	    data[j] += 1 << scanInfo.al;
	  }
	}
      }
      --eobRun;
      break;

    // zero run and one AC coefficient
    } else {
      run = (c >> 4) & 0x0f;
      size = c & 0x0f;
      if ((amp = readAmp(size)) == 9999) {
	return false;
      }
      k = 0;
      do {
	j = dctZigZag[i++];
	while (data[j] != 0) {
	  if ((bit = readBit()) == EOF) {
	    return false;
	  }
	  if (bit) {
	    data[j] += 1 << scanInfo.al;
	  }
	  j = dctZigZag[i++];
	}
	++k;
      } while (k <= run);
      data[j] = amp << scanInfo.al;
    }
  }

  return true;
}

// Decode a progressive JPEG image.
void DCTStream::decodeImage()
{
  int dataIn[64];
  uchar dataOut[64];
  uchar *quantTable;
  int pY, pCb, pCr, pR, pG, pB;
  int x1, y1, x2, y2, x3, y3, x4, y4, x5, y5, cc, i;
  int h, v, horiz, vert, hSub, vSub;
  int *p0, *p1, *p2;

  for (y1 = 0; y1 < bufHeight; y1 += mcuHeight) {
    for (x1 = 0; x1 < bufWidth; x1 += mcuWidth) {
      for (cc = 0; cc < numComps; ++cc) {
	quantTable = quantTables[compInfo[cc].quantTable];
	h = compInfo[cc].hSample;
	v = compInfo[cc].vSample;
	horiz = mcuWidth / h;
	vert = mcuHeight / v;
	hSub = horiz / 8;
	vSub = vert / 8;
	for (y2 = 0; y2 < mcuHeight; y2 += vert) {
	  for (x2 = 0; x2 < mcuWidth; x2 += horiz) {

	    // pull out the coded data unit
	    p1 = &frameBuf[cc][(y1+y2) * bufWidth + (x1+x2)];
	    for (y3 = 0, i = 0; y3 < 8; ++y3, i += 8) {
	      dataIn[i]   = p1[0];
	      dataIn[i+1] = p1[1];
	      dataIn[i+2] = p1[2];
	      dataIn[i+3] = p1[3];
	      dataIn[i+4] = p1[4];
	      dataIn[i+5] = p1[5];
	      dataIn[i+6] = p1[6];
	      dataIn[i+7] = p1[7];
	      p1 += bufWidth * vSub;
	    }

	    // transform
	    transformDataUnit(quantTable, dataIn, dataOut);

	    // store back into frameBuf, doing replication for
	    // subsampled components
	    p1 = &frameBuf[cc][(y1+y2) * bufWidth + (x1+x2)];
	    if (hSub == 1 && vSub == 1) {
	      for (y3 = 0, i = 0; y3 < 8; ++y3, i += 8) {
		p1[0] = dataOut[i] & 0xff;
		p1[1] = dataOut[i+1] & 0xff;
		p1[2] = dataOut[i+2] & 0xff;
		p1[3] = dataOut[i+3] & 0xff;
		p1[4] = dataOut[i+4] & 0xff;
		p1[5] = dataOut[i+5] & 0xff;
		p1[6] = dataOut[i+6] & 0xff;
		p1[7] = dataOut[i+7] & 0xff;
		p1 += bufWidth;
	      }
	    } else if (hSub == 2 && vSub == 2) {
	      p2 = p1 + bufWidth;
	      for (y3 = 0, i = 0; y3 < 16; y3 += 2, i += 8) {
		p1[0] = p1[1] = p2[0] = p2[1] = dataOut[i] & 0xff;
		p1[2] = p1[3] = p2[2] = p2[3] = dataOut[i+1] & 0xff;
		p1[4] = p1[5] = p2[4] = p2[5] = dataOut[i+2] & 0xff;
		p1[6] = p1[7] = p2[6] = p2[7] = dataOut[i+3] & 0xff;
		p1[8] = p1[9] = p2[8] = p2[9] = dataOut[i+4] & 0xff;
		p1[10] = p1[11] = p2[10] = p2[11] = dataOut[i+5] & 0xff;
		p1[12] = p1[13] = p2[12] = p2[13] = dataOut[i+6] & 0xff;
		p1[14] = p1[15] = p2[14] = p2[15] = dataOut[i+7] & 0xff;
		p1 += bufWidth * 2;
		p2 += bufWidth * 2;
	      }
	    } else {
	      i = 0;
	      for (y3 = 0, y4 = 0; y3 < 8; ++y3, y4 += vSub) {
		for (x3 = 0, x4 = 0; x3 < 8; ++x3, x4 += hSub) {
		  p2 = p1 + x4;
		  for (y5 = 0; y5 < vSub; ++y5) {
		    for (x5 = 0; x5 < hSub; ++x5) {
		      p2[x5] = dataOut[i] & 0xff;
		    }
		    p2 += bufWidth;
		  }
		  ++i;
		}
		p1 += bufWidth * vSub;
	      }
	    }
	  }
	}
      }

      // color space conversion
      if (colorXform) {
	// convert YCbCr to RGB
	if (numComps == 3) {
	  for (y2 = 0; y2 < mcuHeight; ++y2) {
	    p0 = &frameBuf[0][(y1+y2) * bufWidth + x1];
	    p1 = &frameBuf[1][(y1+y2) * bufWidth + x1];
	    p2 = &frameBuf[2][(y1+y2) * bufWidth + x1];
	    for (x2 = 0; x2 < mcuWidth; ++x2) {
	      pY = *p0;
	      pCb = *p1 - 128;
	      pCr = *p2 - 128;
	      pR = ((pY << 16) + dctCrToR * pCr + 32768) >> 16;
	      *p0++ = dctClip[dctClipOffset + pR];
	      pG = ((pY << 16) + dctCbToG * pCb + dctCrToG * pCr +
		    32768) >> 16;
	      *p1++ = dctClip[dctClipOffset + pG];
	      pB = ((pY << 16) + dctCbToB * pCb + 32768) >> 16;
	      *p2++ = dctClip[dctClipOffset + pB];
	    }
	  }
	// convert YCbCrK to CMYK (K is passed through unchanged)
	} else if (numComps == 4) {
	  for (y2 = 0; y2 < mcuHeight; ++y2) {
	    p0 = &frameBuf[0][(y1+y2) * bufWidth + x1];
	    p1 = &frameBuf[1][(y1+y2) * bufWidth + x1];
	    p2 = &frameBuf[2][(y1+y2) * bufWidth + x1];
	    for (x2 = 0; x2 < mcuWidth; ++x2) {
	      pY = *p0;
	      pCb = *p1 - 128;
	      pCr = *p2 - 128;
	      pR = ((pY << 16) + dctCrToR * pCr + 32768) >> 16;
	      *p0++ = 255 - dctClip[dctClipOffset + pR];
	      pG = ((pY << 16) + dctCbToG * pCb + dctCrToG * pCr +
		    32768) >> 16;
	      *p1++ = 255 - dctClip[dctClipOffset + pG];
	      pB = ((pY << 16) + dctCbToB * pCb + 32768) >> 16;
	      *p2++ = 255 - dctClip[dctClipOffset + pB];
	    }
	  }
	}
      }
    }
  }
}

// Transform one data unit -- this performs the dequantization and
// IDCT steps.  This IDCT algorithm is taken from:
//   Christoph Loeffler, Adriaan Ligtenberg, George S. Moschytz,
//   "Practical Fast 1-D DCT Algorithms with 11 Multiplications",
//   IEEE Intl. Conf. on Acoustics, Speech & Signal Processing, 1989,
//   988-991.
// The stage numbers mentioned in the comments refer to Figure 1 in this
// paper.
void DCTStream::transformDataUnit(uchar *quantTable,
				  int dataIn[64], uchar dataOut[64])
{
  int v0, v1, v2, v3, v4, v5, v6, v7, t;
  int *p;
  int i;

  // dequant
  for (i = 0; i < 64; ++i) {
    dataIn[i] *= quantTable[i];
  }

  // inverse DCT on rows
  for (i = 0; i < 64; i += 8) {
    p = dataIn + i;

    // check for all-zero AC coefficients
    if (p[1] == 0 && p[2] == 0 && p[3] == 0 &&
	p[4] == 0 && p[5] == 0 && p[6] == 0 && p[7] == 0) {
      t = (dctSqrt2 * p[0] + 512) >> 10;
      p[0] = t;
      p[1] = t;
      p[2] = t;
      p[3] = t;
      p[4] = t;
      p[5] = t;
      p[6] = t;
      p[7] = t;
      continue;
    }

    // stage 4
    v0 = (dctSqrt2 * p[0] + 128) >> 8;
    v1 = (dctSqrt2 * p[4] + 128) >> 8;
    v2 = p[2];
    v3 = p[6];
    v4 = (dctSqrt1d2 * (p[1] - p[7]) + 128) >> 8;
    v7 = (dctSqrt1d2 * (p[1] + p[7]) + 128) >> 8;
    v5 = p[3] << 4;
    v6 = p[5] << 4;

    // stage 3
    t = (v0 - v1+ 1) >> 1;
    v0 = (v0 + v1 + 1) >> 1;
    v1 = t;
    t = (v2 * dctSin6 + v3 * dctCos6 + 128) >> 8;
    v2 = (v2 * dctCos6 - v3 * dctSin6 + 128) >> 8;
    v3 = t;
    t = (v4 - v6 + 1) >> 1;
    v4 = (v4 + v6 + 1) >> 1;
    v6 = t;
    t = (v7 + v5 + 1) >> 1;
    v5 = (v7 - v5 + 1) >> 1;
    v7 = t;

    // stage 2
    t = (v0 - v3 + 1) >> 1;
    v0 = (v0 + v3 + 1) >> 1;
    v3 = t;
    t = (v1 - v2 + 1) >> 1;
    v1 = (v1 + v2 + 1) >> 1;
    v2 = t;
    t = (v4 * dctSin3 + v7 * dctCos3 + 2048) >> 12;
    v4 = (v4 * dctCos3 - v7 * dctSin3 + 2048) >> 12;
    v7 = t;
    t = (v5 * dctSin1 + v6 * dctCos1 + 2048) >> 12;
    v5 = (v5 * dctCos1 - v6 * dctSin1 + 2048) >> 12;
    v6 = t;

    // stage 1
    p[0] = v0 + v7;
    p[7] = v0 - v7;
    p[1] = v1 + v6;
    p[6] = v1 - v6;
    p[2] = v2 + v5;
    p[5] = v2 - v5;
    p[3] = v3 + v4;
    p[4] = v3 - v4;
  }

  // inverse DCT on columns
  for (i = 0; i < 8; ++i) {
    p = dataIn + i;

    // check for all-zero AC coefficients
    if (p[1*8] == 0 && p[2*8] == 0 && p[3*8] == 0 &&
	p[4*8] == 0 && p[5*8] == 0 && p[6*8] == 0 && p[7*8] == 0) {
      t = (dctSqrt2 * dataIn[i+0] + 8192) >> 14;
      p[0*8] = t;
      p[1*8] = t;
      p[2*8] = t;
      p[3*8] = t;
      p[4*8] = t;
      p[5*8] = t;
      p[6*8] = t;
      p[7*8] = t;
      continue;
    }

    // stage 4
    v0 = (dctSqrt2 * p[0*8] + 2048) >> 12;
    v1 = (dctSqrt2 * p[4*8] + 2048) >> 12;
    v2 = p[2*8];
    v3 = p[6*8];
    v4 = (dctSqrt1d2 * (p[1*8] - p[7*8]) + 2048) >> 12;
    v7 = (dctSqrt1d2 * (p[1*8] + p[7*8]) + 2048) >> 12;
    v5 = p[3*8];
    v6 = p[5*8];

    // stage 3
    t = (v0 - v1 + 1) >> 1;
    v0 = (v0 + v1 + 1) >> 1;
    v1 = t;
    t = (v2 * dctSin6 + v3 * dctCos6 + 2048) >> 12;
    v2 = (v2 * dctCos6 - v3 * dctSin6 + 2048) >> 12;
    v3 = t;
    t = (v4 - v6 + 1) >> 1;
    v4 = (v4 + v6 + 1) >> 1;
    v6 = t;
    t = (v7 + v5 + 1) >> 1;
    v5 = (v7 - v5 + 1) >> 1;
    v7 = t;

    // stage 2
    t = (v0 - v3 + 1) >> 1;
    v0 = (v0 + v3 + 1) >> 1;
    v3 = t;
    t = (v1 - v2 + 1) >> 1;
    v1 = (v1 + v2 + 1) >> 1;
    v2 = t;
    t = (v4 * dctSin3 + v7 * dctCos3 + 2048) >> 12;
    v4 = (v4 * dctCos3 - v7 * dctSin3 + 2048) >> 12;
    v7 = t;
    t = (v5 * dctSin1 + v6 * dctCos1 + 2048) >> 12;
    v5 = (v5 * dctCos1 - v6 * dctSin1 + 2048) >> 12;
    v6 = t;

    // stage 1
    p[0*8] = v0 + v7;
    p[7*8] = v0 - v7;
    p[1*8] = v1 + v6;
    p[6*8] = v1 - v6;
    p[2*8] = v2 + v5;
    p[5*8] = v2 - v5;
    p[3*8] = v3 + v4;
    p[4*8] = v3 - v4;
  }

  // convert to 8-bit integers
  for (i = 0; i < 64; ++i) {
    dataOut[i] = dctClip[dctClipOffset + 128 + ((dataIn[i] + 8) >> 4)];
  }
}

int DCTStream::readHuffSym(DCTHuffTable *table)
{
  ushort code;
  int bit;
  int codeBits;

  code = 0;
  codeBits = 0;
  do {
    // add a bit to the code
    if ((bit = readBit()) == EOF)
      return 9999;
    code = ushort((code << 1) + bit);
    ++codeBits;

    // look up code
    if (code - table->firstCode[codeBits] < table->numCodes[codeBits]) {
      code -= table->firstCode[codeBits];
      return table->sym[table->firstSym[codeBits] + code];
    }
  } while (codeBits < 16);

  ipeDebug("Bad Huffman code in DCT stream");
  return 9999;
}

int DCTStream::readAmp(int size)
{
  int amp, bit;
  int bits;

  amp = 0;
  for (bits = 0; bits < size; ++bits) {
    if ((bit = readBit()) == EOF)
      return 9999;
    amp = (amp << 1) + bit;
  }
  if (amp < (1 << (size - 1)))
    amp -= (1 << size) - 1;
  return amp;
}

int DCTStream::readBit()
{
  int bit;
  int c, c2;

  if (inputBits == 0) {
    if ((c = iSource.getChar()) == EOF)
      return EOF;
    if (c == 0xff) {
      do {
	c2 = iSource.getChar();
      } while (c2 == 0xff);
      if (c2 != 0x00) {
	ipeDebug("Bad DCT data: missing 00 after ff");
	return EOF;
      }
    }
    inputBuf = c;
    inputBits = 8;
  }
  bit = (inputBuf >> (inputBits - 1)) & 1;
  --inputBits;
  return bit;
}

bool DCTStream::readHeader()
{
  bool doScan;
  int n;
  int c;
  int i;

  // read headers
  doScan = false;
  while (!doScan) {
    c = readMarker();
    switch (c) {
    case 0xc0:			// SOF0
      if (!readBaselineSOF()) {
	return false;
      }
      break;
    case 0xc2:			// SOF2
      if (!readProgressiveSOF()) {
	return false;
      }
      break;
    case 0xc4:			// DHT
      if (!readHuffmanTables()) {
	return false;
      }
      break;
    case 0xd8:			// SOI
      break;
    case 0xd9:			// EOI
      return false;
    case 0xda:			// SOS
      if (!readScanInfo()) {
	return false;
      }
      doScan = true;
      break;
    case 0xdb:			// DQT
      if (!readQuantTables()) {
	return false;
      }
      break;
    case 0xdd:			// DRI
      if (!readRestartInterval()) {
	return false;
      }
      break;
    case 0xee:			// APP14
      if (!readAdobeMarker()) {
	return false;
      }
      break;
    case EOF:
      ipeDebug("Bad DCT header");
      return false;
    default:
      // skip APPn / COM / etc.
      if (c >= 0xe0) {
	n = read16() - 2;
	for (i = 0; i < n; ++i) {
	  iSource.getChar();
	}
      } else {
	ipeDebug("Unknown DCT marker <%02x>", c);
	return false;
      }
      break;
    }
  }

  return true;
}

bool DCTStream::readBaselineSOF()
{
  (void) read16(); // length
  int prec = iSource.getChar();
  height = read16();
  width = read16();
  numComps = iSource.getChar();
  if (prec != 8) {
    ipeDebug("Bad DCT precision %d", prec);
    return false;
  }
  for (int i = 0; i < numComps; ++i) {
    compInfo[i].id = iSource.getChar();
    int c = iSource.getChar();
    compInfo[i].hSample = (c >> 4) & 0x0f;
    compInfo[i].vSample = c & 0x0f;
    compInfo[i].quantTable = iSource.getChar();
  }
  progressive = false;
  return true;
}

bool DCTStream::readProgressiveSOF()
{
  (void) read16(); // length
  int prec = iSource.getChar();
  height = read16();
  width = read16();
  numComps = iSource.getChar();
  if (prec != 8) {
    ipeDebug("Bad DCT precision %d", prec);
    return false;
  }
  for (int i = 0; i < numComps; ++i) {
    compInfo[i].id = iSource.getChar();
    int c = iSource.getChar();
    compInfo[i].hSample = (c >> 4) & 0x0f;
    compInfo[i].vSample = c & 0x0f;
    compInfo[i].quantTable = iSource.getChar();
  }
  progressive = true;
  return true;
}

bool DCTStream::readScanInfo()
{
  int length;
  int id, c;
  int i, j;

  length = read16() - 2;
  scanInfo.numComps = iSource.getChar();
  --length;
  if (length != 2 * scanInfo.numComps + 3) {
    ipeDebug("Bad DCT scan info block");
    return false;
  }
  interleaved = scanInfo.numComps == numComps;
  for (j = 0; j < numComps; ++j) {
    scanInfo.comp[j] = false;
  }
  for (i = 0; i < scanInfo.numComps; ++i) {
    id = iSource.getChar();
    for (j = 0; j < numComps; ++j) {
      if (id == compInfo[j].id) {
	break;
      }
    }
    if (j == numComps) {
      ipeDebug("Bad DCT component ID in scan info block");
      return false;
    }
    scanInfo.comp[j] = true;
    c = iSource.getChar();
    scanInfo.dcHuffTable[j] = (c >> 4) & 0x0f;
    scanInfo.acHuffTable[j] = c & 0x0f;
  }
  scanInfo.firstCoeff = iSource.getChar();
  scanInfo.lastCoeff = iSource.getChar();
  c = iSource.getChar();
  scanInfo.ah = (c >> 4) & 0x0f;
  scanInfo.al = c & 0x0f;
  return true;
}

bool DCTStream::readQuantTables()
{
  int length;
  int i;
  int index;

  length = read16() - 2;
  while (length > 0) {
    index = iSource.getChar();
    if ((index & 0xf0) || index >= 4) {
      ipeDebug("Bad DCT quantization table");
      return false;
    }
    if (index == numQuantTables)
      numQuantTables = index + 1;
    for (i = 0; i < 64; ++i)
      quantTables[index][dctZigZag[i]] = uchar(iSource.getChar());
    length -= 65;
  }
  return true;
}

bool DCTStream::readHuffmanTables()
{
  DCTHuffTable *tbl;
  int length;
  int index;
  ushort code;
  uchar sym;
  int i;
  int c;

  length = read16() - 2;
  while (length > 0) {
    index = iSource.getChar();
    --length;
    if ((index & 0x0f) >= 4) {
      ipeDebug("Bad DCT Huffman table");
      return false;
    }
    if (index & 0x10) {
      index &= 0x0f;
      if (index >= numACHuffTables)
	numACHuffTables = index+1;
      tbl = &acHuffTables[index];
    } else {
      if (index >= numDCHuffTables)
	numDCHuffTables = index+1;
      tbl = &dcHuffTables[index];
    }
    sym = 0;
    code = 0;
    for (i = 1; i <= 16; ++i) {
      c = iSource.getChar();
      tbl->firstSym[i] = sym;
      tbl->firstCode[i] = code;
      tbl->numCodes[i] = ushort(c);
      sym += uchar(c);
      code = ushort((code + c) << 1);
    }
    length -= 16;
    for (i = 0; i < sym; ++i)
      tbl->sym[i] = uchar(iSource.getChar());
    length -= sym;
  }
  return true;
}

bool DCTStream::readRestartInterval()
{
  int length;

  length = read16();
  if (length != 4) {
    ipeDebug("Bad DCT restart interval");
    return false;
  }
  restartInterval = read16();
  return true;
}

bool DCTStream::readAdobeMarker()
{
  int length, i;
  char buf[12];
  int c;

  length = read16();
  if (length < 14) {
    goto err;
  }
  for (i = 0; i < 12; ++i) {
    if ((c = iSource.getChar()) == EOF) {
      goto err;
    }
    buf[i] = char(c);
  }
  if (::strncmp(buf, "Adobe", 5)) {
    goto err;
  }
  colorXform = buf[11];
  gotAdobeMarker = true;
  for (i = 14; i < length; ++i) {
    if (iSource.getChar() == EOF) {
      goto err;
    }
  }
  return true;

 err:
  ipeDebug("Bad DCT Adobe APP14 marker");
  return false;
}

bool DCTStream::readTrailer()
{
  int c;

  c = readMarker();
  if (c != 0xd9) {		// EOI
    ipeDebug("Bad DCT trailer");
    return false;
  }
  return true;
}

int DCTStream::readMarker()
{
  int c;

  do {
    do {
      c = iSource.getChar();
    } while (c != 0xff);
    do {
      c = iSource.getChar();
    } while (c == 0xff);
  } while (c == 0x00);
  return c;
}

int DCTStream::read16()
{
  int c1, c2;

  if ((c1 = iSource.getChar()) == EOF)
    return EOF;
  if ((c2 = iSource.getChar()) == EOF)
    return EOF;
  return (c1 << 8) + c2;
}

// --------------------------------------------------------------------

bool dctDecode(Buffer dctData, Buffer pixelData)
{
  // ipeDebug("dctDecode %d, %d", dctData.size(), pixelData.size());
  BufferSource source(dctData);
  DCTStream dct(source);
  dct.reset();
  char *p = pixelData.data();
  int n = pixelData.size();
  while (n--) {
    int c = dct.getChar();
    if (c == EOF)
      return false;
    *p++ = char(c);
  }
  return true;
}

// --------------------------------------------------------------------
