text: // jpgd.cpp - C++ class for JPEG decompression.
  // Public domain, Rich Geldreich <richgel99@gmail.com>
  // Alex Evans: Linear memory allocator (taken from jpge.h).
  // v1.04, May. 19, 2012: Code tweaks to fix VS2008 static code analysis warnings (all looked harmless)
  // changes from upstream, May.  5 2014: Fix harmless VC++ warning C4703
  //                        Feb. 24 2015: Suppress VC++ warning C4458 without clear fix
  //
  // Supports progressive and baseline sequential JPEG image files, and the most common chroma subsampling factors: Y, H1V1, H2V1, H1V2, and H2V2.
  //
  // Chroma upsampling quality: H2V2 is upsampled in the frequency domain, H2V1 and H1V2 are upsampled using point sampling.
  // Chroma upsampling reference: "Fast Scheme for Image Size Change in the Compressed Domain"
  // http://vision.ai.uiuc.edu/~dugad/research/dct/index.html
  
  #include "jpgd.h"
  #include <string.h>
  
  #include <assert.h>
  #define JPGD_ASSERT(x) assert(x)
  
  #ifdef _MSC_VER
  #pragma warning (disable : 4611) // warning C4611: interaction between '_setjmp' and C++ object destruction is non-portable
  #pragma warning (disable : 4458) // warning C4458: declaration of 'm_block_y_mcu' hides class member in decode_scan()
  #endif
  
  // Set to 1 to enable freq. domain chroma upsampling on images using H2V2 subsampling (0=faster nearest neighbor sampling).
  // This is slower, but results in higher quality on images with highly saturated colors.
  #define JPGD_SUPPORT_FREQ_DOMAIN_UPSAMPLING 1
  
  #define JPGD_TRUE (1)
  #define JPGD_FALSE (0)
  
  #define JPGD_MAX(a,b) (((a)>(b)) ? (a) : (b))
  #define JPGD_MIN(a,b) (((a)<(b)) ? (a) : (b))
  
  namespace jpgd {
  
  static inline void *jpgd_malloc(size_t nSize) { return malloc(nSize); }
  static inline void jpgd_free(void *p) { free(p); }
  
  // DCT coefficients are stored in this sequence.
  static int g_ZAG[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 };
  
  enum JPEG_MARKER
  {
    M_SOF0  = 0xC0, M_SOF1  = 0xC1, M_SOF2  = 0xC2, M_SOF3  = 0xC3, M_SOF5  = 0xC5, M_SOF6  = 0xC6, M_SOF7  = 0xC7, M_JPG   = 0xC8,
    M_SOF9  = 0xC9, M_SOF10 = 0xCA, M_SOF11 = 0xCB, M_SOF13 = 0xCD, M_SOF14 = 0xCE, M_SOF15 = 0xCF, M_DHT   = 0xC4, M_DAC   = 0xCC,
    M_RST0  = 0xD0, M_RST1  = 0xD1, M_RST2  = 0xD2, M_RST3  = 0xD3, M_RST4  = 0xD4, M_RST5  = 0xD5, M_RST6  = 0xD6, M_RST7  = 0xD7,
    M_SOI   = 0xD8, M_EOI   = 0xD9, M_SOS   = 0xDA, M_DQT   = 0xDB, M_DNL   = 0xDC, M_DRI   = 0xDD, M_DHP   = 0xDE, M_EXP   = 0xDF,
    M_APP0  = 0xE0, M_APP15 = 0xEF, M_JPG0  = 0xF0, M_JPG13 = 0xFD, M_COM   = 0xFE, M_TEM   = 0x01, M_ERROR = 0x100, RST0   = 0xD0
  };
  
  enum JPEG_SUBSAMPLING { JPGD_GRAYSCALE = 0, JPGD_YH1V1, JPGD_YH2V1, JPGD_YH1V2, JPGD_YH2V2 };
  
  #define CONST_BITS  13
  #define PASS1_BITS  2
  #define SCALEDONE ((int32)1)
  
  #define FIX_0_298631336  ((int32)2446)        /* FIX(0.298631336) */
  #define FIX_0_390180644  ((int32)3196)        /* FIX(0.390180644) */
  #define FIX_0_541196100  ((int32)4433)        /* FIX(0.541196100) */
  #define FIX_0_765366865  ((int32)6270)        /* FIX(0.765366865) */
  #define FIX_0_899976223  ((int32)7373)        /* FIX(0.899976223) */
  #define FIX_1_175875602  ((int32)9633)        /* FIX(1.175875602) */
  #define FIX_1_501321110  ((int32)12299)       /* FIX(1.501321110) */
  #define FIX_1_847759065  ((int32)15137)       /* FIX(1.847759065) */
  #define FIX_1_961570560  ((int32)16069)       /* FIX(1.961570560) */
  #define FIX_2_053119869  ((int32)16819)       /* FIX(2.053119869) */
  #define FIX_2_562915447  ((int32)20995)       /* FIX(2.562915447) */
  #define FIX_3_072711026  ((int32)25172)       /* FIX(3.072711026) */
  
  #define DESCALE(x,n)  (((x) + (SCALEDONE << ((n)-1))) >> (n))
  #define DESCALE_ZEROSHIFT(x,n)  (((x) + (128 << (n)) + (SCALEDONE << ((n)-1))) >> (n))
  
  #define MULTIPLY(var, cnst)  ((var) * (cnst))
  
  #define CLAMP(i) ((static_cast<uint>(i) > 255) ? (((~i) >> 31) & 0xFF) : (i))
  
  // Compiler creates a fast path 1D IDCT for X non-zero columns
  template <int NONZERO_COLS>
  struct Row
  {
    static void idct(int* pTemp, const jpgd_block_t* pSrc)
    {
      // ACCESS_COL() will be optimized at compile time to either an array access, or 0.
      #define ACCESS_COL(x) (((x) < NONZERO_COLS) ? (int)pSrc[x] : 0)
  
      const int z2 = ACCESS_COL(2), z3 = ACCESS_COL(6);
  
      const int z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
      const int tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
      const int tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
  
      const int tmp0 = (ACCESS_COL(0) + ACCESS_COL(4)) << CONST_BITS;
      const int tmp1 = (ACCESS_COL(0) - ACCESS_COL(4)) << CONST_BITS;
  
      const int tmp10 = tmp0 + tmp3, tmp13 = tmp0 - tmp3, tmp11 = tmp1 + tmp2, tmp12 = tmp1 - tmp2;
  
      const int atmp0 = ACCESS_COL(7), atmp1 = ACCESS_COL(5), atmp2 = ACCESS_COL(3), atmp3 = ACCESS_COL(1);
  
      const int bz1 = atmp0 + atmp3, bz2 = atmp1 + atmp2, bz3 = atmp0 + atmp2, bz4 = atmp1 + atmp3;
      const int bz5 = MULTIPLY(bz3 + bz4, FIX_1_175875602);
  
      const int az1 = MULTIPLY(bz1, - FIX_0_899976223);
      const int az2 = MULTIPLY(bz2, - FIX_2_562915447);
      const int az3 = MULTIPLY(bz3, - FIX_1_961570560) + bz5;
      const int az4 = MULTIPLY(bz4, - FIX_0_390180644) + bz5;
  
      const int btmp0 = MULTIPLY(atmp0, FIX_0_298631336) + az1 + az3;
      const int btmp1 = MULTIPLY(atmp1, FIX_2_053119869) + az2 + az4;
      const int btmp2 = MULTIPLY(atmp2, FIX_3_072711026) + az2 + az3;
      const int btmp3 = MULTIPLY(atmp3, FIX_1_501321110) + az1 + az4;
  
      pTemp[0] = DESCALE(tmp10 + btmp3, CONST_BITS-PASS1_BITS);
      pTemp[7] = DESCALE(tmp10 - btmp3, CONST_BITS-PASS1_BITS);
      pTemp[1] = DESCALE(tmp11 + btmp2, CONST_BITS-PASS1_BITS);
      pTemp[6] = DESCALE(tmp11 - btmp2, CONST_BITS-PASS1_BITS);
      pTemp[2] = DESCALE(tmp12 + btmp1, CONST_BITS-PASS1_BITS);
      pTemp[5] = DESCALE(tmp12 - btmp1, CONST_BITS-PASS1_BITS);
      pTemp[3] = DESCALE(tmp13 + btmp0, CONST_BITS-PASS1_BITS);
      pTemp[4] = DESCALE(tmp13 - btmp0, CONST_BITS-PASS1_BITS);
    }
  };
  
  template <>
  struct Row<0>
  {
    static void idct(int* pTemp, const jpgd_block_t* pSrc)
    {
  #ifdef _MSC_VER
      pTemp; pSrc;
  #endif
    }
  };
  
  template <>
  struct Row<1>
  {
    static void idct(int* pTemp, const jpgd_block_t* pSrc)
    {
      const int dcval = (pSrc[0] << PASS1_BITS);
  
      pTemp[0] = dcval;
      pTemp[1] = dcval;
      pTemp[2] = dcval;
      pTemp[3] = dcval;
      pTemp[4] = dcval;
      pTemp[5] = dcval;
      pTemp[6] = dcval;
      pTemp[7] = dcval;
    }
  };
  
  // Compiler creates a fast path 1D IDCT for X non-zero rows
  template <int NONZERO_ROWS>
  struct Col
  {
    static void idct(uint8* pDst_ptr, const int* pTemp)
    {
      // ACCESS_ROW() will be optimized at compile time to either an array access, or 0.
      #define ACCESS_ROW(x) (((x) < NONZERO_ROWS) ? pTemp[x * 8] : 0)
  
      const int z2 = ACCESS_ROW(2);
      const int z3 = ACCESS_ROW(6);
  
      const int z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
      const int tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
      const int tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
  
      const int tmp0 = (ACCESS_ROW(0) + ACCESS_ROW(4)) << CONST_BITS;
      const int tmp1 = (ACCESS_ROW(0) - ACCESS_ROW(4)) << CONST_BITS;
  
      const int tmp10 = tmp0 + tmp3, tmp13 = tmp0 - tmp3, tmp11 = tmp1 + tmp2, tmp12 = tmp1 - tmp2;
  
      const int atmp0 = ACCESS_ROW(7), atmp1 = ACCESS_ROW(5), atmp2 = ACCESS_ROW(3), atmp3 = ACCESS_ROW(1);
  
      const int bz1 = atmp0 + atmp3, bz2 = atmp1 + atmp2, bz3 = atmp0 + atmp2, bz4 = atmp1 + atmp3;
      const int bz5 = MULTIPLY(bz3 + bz4, FIX_1_175875602);
  
      const int az1 = MULTIPLY(bz1, - FIX_0_899976223);
      const int az2 = MULTIPLY(bz2, - FIX_2_562915447);
      const int az3 = MULTIPLY(bz3, - FIX_1_961570560) + bz5;
      const int az4 = MULTIPLY(bz4, - FIX_0_390180644) + bz5;
  
      const int btmp0 = MULTIPLY(atmp0, FIX_0_298631336) + az1 + az3;
      const int btmp1 = MULTIPLY(atmp1, FIX_2_053119869) + az2 + az4;
      const int btmp2 = MULTIPLY(atmp2, FIX_3_072711026) + az2 + az3;
      const int btmp3 = MULTIPLY(atmp3, FIX_1_501321110) + az1 + az4;
  
      int i = DESCALE_ZEROSHIFT(tmp10 + btmp3, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*0] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp10 - btmp3, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*7] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp11 + btmp2, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*1] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp11 - btmp2, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*6] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp12 + btmp1, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*2] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp12 - btmp1, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*5] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp13 + btmp0, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*3] = (uint8)CLAMP(i);
  
      i = DESCALE_ZEROSHIFT(tmp13 - btmp0, CONST_BITS+PASS1_BITS+3);
      pDst_ptr[8*4] = (uint8)CLAMP(i);
    }
  };
  
  template <>
  struct Col<1>
  {
    static void idct(uint8* pDst_ptr, const int* pTemp)
    {
      int dcval = DESCALE_ZEROSHIFT(pTemp[0], PASS1_BITS+3);
      const uint8 dcval_clamped = (uint8)CLAMP(dcval);
      pDst_ptr[0*8] = dcval_clamped;
      pDst_ptr[1*8] = dcval_clamped;
      pDst_ptr[2*8] = dcval_clamped;
      pDst_ptr[3*8] = dcval_clamped;
      pDst_ptr[4*8] = dcval_clamped;
      pDst_ptr[5*8] = dcval_clamped;
      pDst_ptr[6*8] = dcval_clamped;
      pDst_ptr[7*8] = dcval_clamped;
    }
  };
  
  static const uint8 s_idct_row_table[] =
  {
    1,0,0,0,0,0,0,0, 2,0,0,0,0,0,0,0, 2,1,0,0,0,0,0,0, 2,1,1,0,0,0,0,0, 2,2,1,0,0,0,0,0, 3,2,1,0,0,0,0,0, 4,2,1,0,0,0,0,0, 4,3,1,0,0,0,0,0,
    4,3,2,0,0,0,0,0, 4,3,2,1,0,0,0,0, 4,3,2,1,1,0,0,0, 4,3,2,2,1,0,0,0, 4,3,3,2,1,0,0,0, 4,4,3,2,1,0,0,0, 5,4,3,2,1,0,0,0, 6,4,3,2,1,0,0,0,
    6,5,3,2,1,0,0,0, 6,5,4,2,1,0,0,0, 6,5,4,3,1,0,0,0, 6,5,4,3,2,0,0,0, 6,5,4,3,2,1,0,0, 6,5,4,3,2,1,1,0, 6,5,4,3,2,2,1,0, 6,5,4,3,3,2,1,0,
    6,5,4,4,3,2,1,0, 6,5,5,4,3,2,1,0, 6,6,5,4,3,2,1,0, 7,6,5,4,3,2,1,0, 8,6,5,4,3,2,1,0, 8,7,5,4,3,2,1,0, 8,7,6,4,3,2,1,0, 8,7,6,5,3,2,1,0,
    8,7,6,5,4,2,1,0, 8,7,6,5,4,3,1,0, 8,7,6,5,4,3,2,0, 8,7,6,5,4,3,2,1, 8,7,6,5,4,3,2,2, 8,7,6,5,4,3,3,2, 8,7,6,5,4,4,3,2, 8,7,6,5,5,4,3,2,
    8,7,6,6,5,4,3,2, 8,7,7,6,5,4,3,2, 8,8,7,6,5,4,3,2, 8,8,8,6,5,4,3,2, 8,8,8,7,5,4,3,2, 8,8,8,7,6,4,3,2, 8,8,8,7,6,5,3,2, 8,8,8,7,6,5,4,2,
    8,8,8,7,6,5,4,3, 8,8,8,7,6,5,4,4, 8,8,8,7,6,5,5,4, 8,8,8,7,6,6,5,4, 8,8,8,7,7,6,5,4, 8,8,8,8,7,6,5,4, 8,8,8,8,8,6,5,4, 8,8,8,8,8,7,5,4,
    8,8,8,8,8,7,6,4, 8,8,8,8,8,7,6,5, 8,8,8,8,8,7,6,6, 8,8,8,8,8,7,7,6, 8,8,8,8,8,8,7,6, 8,8,8,8,8,8,8,6, 8,8,8,8,8,8,8,7, 8,8,8,8,8,8,8,8,
  };
  
  static const uint8 s_idct_col_table[] = { 1, 1, 2, 3, 3, 3, 3, 3, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 };
  
  void idct(const jpgd_block_t* pSrc_ptr, uint8* pDst_ptr, int block_max_zag)
  {
    JPGD_ASSERT(block_max_zag >= 1);
    JPGD_ASSERT(block_max_zag <= 64);
  
    if (block_max_zag <= 1)
    {
      int k = ((pSrc_ptr[0] + 4) >> 3) + 128;
      k = CLAMP(k);
      k = k | (k<<8);
      k = k | (k<<16);
  
      for (int i = 8; i > 0; i--)
      {
        *(int*)&pDst_ptr[0] = k;
        *(int*)&pDst_ptr[4] = k;
        pDst_ptr += 8;
      }
      return;
    }
  
    int temp[64];
  
    const jpgd_block_t* pSrc = pSrc_ptr;
    int* pTemp = temp;
  
    const uint8* pRow_tab = &s_idct_row_table[(block_max_zag - 1) * 8];
    int i;
    for (i = 8; i > 0; i--, pRow_tab++)
    {
      switch (*pRow_tab)
      {
        case 0: Row<0>::idct(pTemp, pSrc); break;
        case 1: Row<1>::idct(pTemp, pSrc); break;
        case 2: Row<2>::idct(pTemp, pSrc); break;
        case 3: Row<3>::idct(pTemp, pSrc); break;
        case 4: Row<4>::idct(pTemp, pSrc); break;
        case 5: Row<5>::idct(pTemp, pSrc); break;
        case 6: Row<6>::idct(pTemp, pSrc); break;
        case 7: Row<7>::idct(pTemp, pSrc); break;
        case 8: Row<8>::idct(pTemp, pSrc); break;
      }
  
      pSrc += 8;
      pTemp += 8;
    }
  
    pTemp = temp;
  
    const int nonzero_rows = s_idct_col_table[block_max_zag - 1];
    for (i = 8; i > 0; i--)
    {
      switch (nonzero_rows)
      {
        case 1: Col<1>::idct(pDst_ptr, pTemp); break;
        case 2: Col<2>::idct(pDst_ptr, pTemp); break;
        case 3: Col<3>::idct(pDst_ptr, pTemp); break;
        case 4: Col<4>::idct(pDst_ptr, pTemp); break;
        case 5: Col<5>::idct(pDst_ptr, pTemp); break;
        case 6: Col<6>::idct(pDst_ptr, pTemp); break;
        case 7: Col<7>::idct(pDst_ptr, pTemp); break;
        case 8: Col<8>::idct(pDst_ptr, pTemp); break;
      }
  
      pTemp++;
      pDst_ptr++;
    }
  }
  
  void idct_4x4(const jpgd_block_t* pSrc_ptr, uint8* pDst_ptr)
  {
    int temp[64];
    int* pTemp = temp;
    const jpgd_block_t* pSrc = pSrc_ptr;
  
    for (int i = 4; i > 0; i--)
    {
      Row<4>::idct(pTemp, pSrc);
      pSrc += 8;
      pTemp += 8;
    }
  
    pTemp = temp;
    for (int i = 8; i > 0; i--)
    {
      Col<4>::idct(pDst_ptr, pTemp);
      pTemp++;
      pDst_ptr++;
    }
  }
  
  // Retrieve one character from the input stream.
  inline uint jpeg_decoder::get_char()
  {
    // Any bytes remaining in buffer?
    if (!m_in_buf_left)
    {
      // Try to get more bytes.
      prep_in_buffer();
      // Still nothing to get?
      if (!m_in_buf_left)
      {
        // Pad the end of the stream with 0xFF 0xD9 (EOI marker)
        int t = m_tem_flag;
        m_tem_flag ^= 1;
        if (t)
          return 0xD9;
        else
          return 0xFF;
      }
    }
  
    uint c = *m_pIn_buf_ofs++;
    m_in_buf_left--;
  
    return c;
  }
  
  // Same as previous method, except can indicate if the character is a pad character or not.
  inline uint jpeg_decoder::get_char(bool *pPadding_flag)
  {
    if (!m_in_buf_left)
    {
      prep_in_buffer();
      if (!m_in_buf_left)
      {
        *pPadding_flag = true;
        int t = m_tem_flag;
        m_tem_flag ^= 1;
        if (t)
          return 0xD9;
        else
          return 0xFF;
      }
    }
  
    *pPadding_flag = false;
  
    uint c = *m_pIn_buf_ofs++;
    m_in_buf_left--;
  
    return c;
  }
  
  // Inserts a previously retrieved character back into the input buffer.
  inline void jpeg_decoder::stuff_char(uint8 q)
  {
    *(--m_pIn_buf_ofs) = q;
    m_in_buf_left++;
  }
  
  // Retrieves one character from the input stream, but does not read past markers. Will continue to return 0xFF when a marker is encountered.
  inline uint8 jpeg_decoder::get_octet()
  {
    bool padding_flag;
    int c = get_char(&padding_flag);
  
    if (c == 0xFF)
    {
      if (padding_flag)
        return 0xFF;
  
      c = get_char(&padding_flag);
      if (padding_flag)
      {
        stuff_char(0xFF);
        return 0xFF;
      }
  
      if (c == 0x00)
        return 0xFF;
      else
      {
        stuff_char(static_cast<uint8>(c));
        stuff_char(0xFF);
        return 0xFF;
      }
    }
  
    return static_cast<uint8>(c);
  }
  
  // Retrieves a variable number of bits from the input stream. Does not recognize markers.
  inline uint jpeg_decoder::get_bits(int num_bits)
  {
    if (!num_bits)
      return 0;
  
    uint i = m_bit_buf >> (32 - num_bits);
  
    if ((m_bits_left -= num_bits) <= 0)
    {
      m_bit_buf <<= (num_bits += m_bits_left);
  
      uint c1 = get_char();
      uint c2 = get_char();
      m_bit_buf = (m_bit_buf & 0xFFFF0000) | (c1 << 8) | c2;
  
      m_bit_buf <<= -m_bits_left;
  
      m_bits_left += 16;
  
      JPGD_ASSERT(m_bits_left >= 0);
    }
    else
      m_bit_buf <<= num_bits;
  
    return i;
  }
  
  // Retrieves a variable number of bits from the input stream. Markers will not be read into the input bit buffer. Instead, an infinite number of all 1's will be returned when a marker is encountered.
  inline uint jpeg_decoder::get_bits_no_markers(int num_bits)
  {
    if (!num_bits)
      return 0;
  
    uint i = m_bit_buf >> (32 - num_bits);
  
    if ((m_bits_left -= num_bits) <= 0)
    {
      m_bit_buf <<= (num_bits += m_bits_left);
  
      if ((m_in_buf_left < 2) || (m_pIn_buf_ofs[0] == 0xFF) || (m_pIn_buf_ofs[1] == 0xFF))
      {
        uint c1 = get_octet();
        uint c2 = get_octet();
        m_bit_buf |= (c1 << 8) | c2;
      }
      else
      {
        m_bit_buf |= ((uint)m_pIn_buf_ofs[0] << 8) | m_pIn_buf_ofs[1];
        m_in_buf_left -= 2;
        m_pIn_buf_ofs += 2;
      }
  
      m_bit_buf <<= -m_bits_left;
  
      m_bits_left += 16;
  
      JPGD_ASSERT(m_bits_left >= 0);
    }
    else
      m_bit_buf <<= num_bits;
  
    return i;
  }
  
  // Decodes a Huffman encoded symbol.
  inline int jpeg_decoder::huff_decode(huff_tables *pH)
  {
    int symbol;
  
    // Check first 8-bits: do we have a complete symbol?
    if ((symbol = pH->look_up[m_bit_buf >> 24]) < 0)
    {
      // Decode more bits, use a tree traversal to find symbol.
      int ofs = 23;
      do
      {
        symbol = pH->tree[-(int)(symbol + ((m_bit_buf >> ofs) & 1))];
        ofs--;
      } while (symbol < 0);
  
      get_bits_no_markers(8 + (23 - ofs));
    }
    else
      get_bits_no_markers(pH->code_size[symbol]);
  
    return symbol;
  }
  
  // Decodes a Huffman encoded symbol.
  inline int jpeg_decoder::huff_decode(huff_tables *pH, int& extra_bits)
  {
    int symbol;
  
    // Check first 8-bits: do we have a complete symbol?
    if ((symbol = pH->look_up2[m_bit_buf >> 24]) < 0)
    {
      // Use a tree traversal to find symbol.
      int ofs = 23;
      do
      {
        symbol = pH->tree[-(int)(symbol + ((m_bit_buf >> ofs) & 1))];
        ofs--;
      } while (symbol < 0);
  
      get_bits_no_markers(8 + (23 - ofs));
  
      extra_bits = get_bits_no_markers(symbol & 0xF);
    }
    else
    {
      JPGD_ASSERT(((symbol >> 8) & 31) == pH->code_size[symbol & 255] + ((symbol & 0x8000) ? (symbol & 15) : 0));
  
      if (symbol & 0x8000)
      {
        get_bits_no_markers((symbol >> 8) & 31);
        extra_bits = symbol >> 16;
      }
      else
      {
        int code_size = (symbol >> 8) & 31;
        int num_extra_bits = symbol & 0xF;
        int bits = code_size + num_extra_bits;
        if (bits <= (m_bits_left + 16))
          extra_bits = get_bits_no_markers(bits) & ((1 << num_extra_bits) - 1);
        else
        {
          get_bits_no_markers(code_size);
          extra_bits = get_bits_no_markers(num_extra_bits);
        }
      }
  
      symbol &= 0xFF;
    }
  
    return symbol;
  }
  
  // Tables and macro used to fully decode the DPCM differences.
  static const int s_extend_test[16] = { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
  static const int s_extend_offset[16] = { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
  static const int s_extend_mask[] = { 0, (1<<0), (1<<1), (1<<2), (1<<3), (1<<4), (1<<5), (1<<6), (1<<7), (1<<8), (1<<9), (1<<10), (1<<11), (1<<12), (1<<13), (1<<14), (1<<15), (1<<16) };
  // The logical AND's in this macro are to shut up static code analysis (aren't really necessary - couldn't find another way to do this)
  #define JPGD_HUFF_EXTEND(x, s) (((x) < s_extend_test[s & 15]) ? ((x) + s_extend_offset[s & 15]) : (x))
  
  // Clamps a value between 0-255.
  inline uint8 jpeg_decoder::clamp(int i)
  {
    if (static_cast<uint>(i) > 255)
      i = (((~i) >> 31) & 0xFF);
  
    return static_cast<uint8>(i);
  }
  
  namespace DCT_Upsample
  {
    struct Matrix44
    {
      typedef int Element_Type;
      enum { NUM_ROWS = 4, NUM_COLS = 4 };
  
      Element_Type v[NUM_ROWS][NUM_COLS];
  
      inline int rows() const { return NUM_ROWS; }
      inline int cols() const { return NUM_COLS; }
  
      inline const Element_Type & at(int r, int c) const { return v[r][c]; }
      inline       Element_Type & at(int r, int c)       { return v[r][c]; }
  
      inline Matrix44() { }
  
      inline Matrix44& operator += (const Matrix44& a)
      {
        for (int r = 0; r < NUM_ROWS; r++)
        {
          at(r, 0) += a.at(r, 0);
          at(r, 1) += a.at(r, 1);
          at(r, 2) += a.at(r, 2);
          at(r, 3) += a.at(r, 3);
        }
        return *this;
      }
  
      inline Matrix44& operator -= (const Matrix44& a)
      {
        for (int r = 0; r < NUM_ROWS; r++)
        {
          at(r, 0) -= a.at(r, 0);
          at(r, 1) -= a.at(r, 1);
          at(r, 2) -= a.at(r, 2);
          at(r, 3) -= a.at(r, 3);
        }
        return *this;
      }
  
      friend inline Matrix44 operator + (const Matrix44& a, const Matrix44& b)
      {
        Matrix44 ret;
        for (int r = 0; r < NUM_ROWS; r++)
        {
          ret.at(r, 0) = a.at(r, 0) + b.at(r, 0);
          ret.at(r, 1) = a.at(r, 1) + b.at(r, 1);
          ret.at(r, 2) = a.at(r, 2) + b.at(r, 2);
          ret.at(r, 3) = a.at(r, 3) + b.at(r, 3);
        }
        return ret;
      }
  
      friend inline Matrix44 operator - (const Matrix44& a, const Matrix44& b)
      {
        Matrix44 ret;
        for (int r = 0; r < NUM_ROWS; r++)
        {
          ret.at(r, 0) = a.at(r, 0) - b.at(r, 0);
          ret.at(r, 1) = a.at(r, 1) - b.at(r, 1);
          ret.at(r, 2) = a.at(r, 2) - b.at(r, 2);
          ret.at(r, 3) = a.at(r, 3) - b.at(r, 3);
        }
        return ret;
      }
  
      static inline void add_and_store(jpgd_block_t* pDst, const Matrix44& a, const Matrix44& b)
      {
        for (int r = 0; r < 4; r++)
        {
          pDst[0*8 + r] = static_cast<jpgd_block_t>(a.at(r, 0) + b.at(r, 0));
          pDst[1*8 + r] = static_cast<jpgd_block_t>(a.at(r, 1) + b.at(r, 1));
          pDst[2*8 + r] = static_cast<jpgd_block_t>(a.at(r, 2) + b.at(r, 2));
          pDst[3*8 + r] = static_cast<jpgd_block_t>(a.at(r, 3) + b.at(r, 3));
        }
      }
  
      static inline void sub_and_store(jpgd_block_t* pDst, const Matrix44& a, const Matrix44& b)
      {
        for (int r = 0; r < 4; r++)
        {
          pDst[0*8 + r] = static_cast<jpgd_block_t>(a.at(r, 0) - b.at(r, 0));
          pDst[1*8 + r] = static_cast<jpgd_block_t>(a.at(r, 1) - b.at(r, 1));
          pDst[2*8 + r] = static_cast<jpgd_block_t>(a.at(r, 2) - b.at(r, 2));
          pDst[3*8 + r] = static_cast<jpgd_block_t>(a.at(r, 3) - b.at(r, 3));
        }
      }
    };
  
    const int FRACT_BITS = 10;
    const int SCALE = 1 << FRACT_BITS;
  
    typedef int Temp_Type;
    #define D(i) (((i) + (SCALE >> 1)) >> FRACT_BITS)
    #define F(i) ((int)((i) * SCALE + .5f))
  
    // Any decent C++ compiler will optimize this at compile time to a 0, or an array access.
    #define AT(c, r) ((((c)>=NUM_COLS)||((r)>=NUM_ROWS)) ? 0 : pSrc[(c)+(r)*8])
  
    // NUM_ROWS/NUM_COLS = # of non-zero rows/cols in input matrix
    template<int NUM_ROWS, int NUM_COLS>
    struct P_Q
    {
      static void calc(Matrix44& P, Matrix44& Q, const jpgd_block_t* pSrc)
      {
        // 4x8 = 4x8 times 8x8, matrix 0 is constant
        const Temp_Type X000 = AT(0, 0);
        const Temp_Type X001 = AT(0, 1);
        const Temp_Type X002 = AT(0, 2);
        const Temp_Type X003 = AT(0, 3);
        const Temp_Type X004 = AT(0, 4);
        const Temp_Type X005 = AT(0, 5);
        const Temp_Type X006 = AT(0, 6);
        const Temp_Type X007 = AT(0, 7);
        const Temp_Type X010 = D(F(0.415735f) * AT(1, 0) + F(0.791065f) * AT(3, 0) + F(-0.352443f) * AT(5, 0) + F(0.277785f) * AT(7, 0));
        const Temp_Type X011 = D(F(0.415735f) * AT(1, 1) + F(0.791065f) * AT(3, 1) + F(-0.352443f) * AT(5, 1) + F(0.277785f) * AT(7, 1));
        const Temp_Type X012 = D(F(0.415735f) * AT(1, 2) + F(0.791065f) * AT(3, 2) + F(-0.352443f) * AT(5, 2) + F(0.277785f) * AT(7, 2));
        const Temp_Type X013 = D(F(0.415735f) * AT(1, 3) + F(0.791065f) * AT(3, 3) + F(-0.352443f) * AT(5, 3) + F(0.277785f) * AT(7, 3));
        const Temp_Type X014 = D(F(0.415735f) * AT(1, 4) + F(0.791065f) * AT(3, 4) + F(-0.352443f) * AT(5, 4) + F(0.277785f) * AT(7, 4));
        const Temp_Type X015 = D(F(0.415735f) * AT(1, 5) + F(0.791065f) * AT(3, 5) + F(-0.352443f) * AT(5, 5) + F(0.277785f) * AT(7, 5));
        const Temp_Type X016 = D(F(0.415735f) * AT(1, 6) + F(0.791065f) * AT(3, 6) + F(-0.352443f) * AT(5, 6) + F(0.277785f) * AT(7, 6));
        const Temp_Type X017 = D(F(0.415735f) * AT(1, 7) + F(0.791065f) * AT(3, 7) + F(-0.352443f) * AT(5, 7) + F(0.277785f) * AT(7, 7));
        const Temp_Type X020 = AT(4, 0);
        const Temp_Type X021 = AT(4, 1);
        const Temp_Type X022 = AT(4, 2);
        const Temp_Type X023 = AT(4, 3);
        const Temp_Type X024 = AT(4, 4);
        const Temp_Type X025 = AT(4, 5);
        const Temp_Type X026 = AT(4, 6);
        const Temp_Type X027 = AT(4, 7);
        const Temp_Type X030 = D(F(0.022887f) * AT(1, 0) + F(-0.097545f) * AT(3, 0) + F(0.490393f) * AT(5, 0) + F(0.865723f) * AT(7, 0));
        const Temp_Type X031 = D(F(0.022887f) * AT(1, 1) + F(-0.097545f) * AT(3, 1) + F(0.490393f) * AT(5, 1) + F(0.865723f) * AT(7, 1));
        const Temp_Type X032 = D(F(0.022887f) * AT(1, 2) + F(-0.097545f) * AT(3, 2) + F(0.490393f) * AT(5, 2) + F(0.865723f) * AT(7, 2));
        const Temp_Type X033 = D(F(0.022887f) * AT(1, 3) + F(-0.097545f) * AT(3, 3) + F(0.490393f) * AT(5, 3) + F(0.865723f) * AT(7, 3));
        const Temp_Type X034 = D(F(0.022887f) * AT(1, 4) + F(-0.097545f) * AT(3, 4) + F(0.490393f) * AT(5, 4) + F(0.865723f) * AT(7, 4));
        const Temp_Type X035 = D(F(0.022887f) * AT(1, 5) + F(-0.097545f) * AT(3, 5) + F(0.490393f) * AT(5, 5) + F(0.865723f) * AT(7, 5));
        const Temp_Type X036 = D(F(0.022887f) * AT(1, 6) + F(-0.097545f) * AT(3, 6) + F(0.490393f) * AT(5, 6) + F(0.865723f) * AT(7, 6));
        const Temp_Type X037 = D(F(0.022887f) * AT(1, 7) + F(-0.097545f) * AT(3, 7) + F(0.490393f) * AT(5, 7) + F(0.865723f) * AT(7, 7));
  
        // 4x4 = 4x8 times 8x4, matrix 1 is constant
        P.at(0, 0) = X000;
        P.at(0, 1) = D(X001 * F(0.415735f) + X003 * F(0.791065f) + X005 * F(-0.352443f) + X007 * F(0.277785f));
        P.at(0, 2) = X004;
        P.at(0, 3) = D(X001 * F(0.022887f) + X003 * F(-0.097545f) + X005 * F(0.490393f) + X007 * F(0.865723f));
        P.at(1, 0) = X010;
        P.at(1, 1) = D(X011 * F(0.415735f) + X013 * F(0.791065f) + X015 * F(-0.352443f) + X017 * F(0.277785f));
        P.at(1, 2) = X014;
        P.at(1, 3) = D(X011 * F(0.022887f) + X013 * F(-0.097545f) + X015 * F(0.490393f) + X017 * F(0.865723f));
        P.at(2, 0) = X020;
        P.at(2, 1) = D(X021 * F(0.415735f) + X023 * F(0.791065f) + X025 * F(-0.352443f) + X027 * F(0.277785f));
        P.at(2, 2) = X024;
        P.at(2, 3) = D(X021 * F(0.022887f) + X023 * F(-0.097545f) + X025 * F(0.490393f) + X027 * F(0.865723f));
        P.at(3, 0) = X030;
        P.at(3, 1) = D(X031 * F(0.415735f) + X033 * F(0.791065f) + X035 * F(-0.352443f) + X037 * F(0.277785f));
        P.at(3, 2) = X034;
        P.at(3, 3) = D(X031 * F(0.022887f) + X033 * F(-0.097545f) + X035 * F(0.490393f) + X037 * F(0.865723f));
        // 40 muls 24 adds
  
        // 4x4 = 4x8 times 8x4, matrix 1 is constant
        Q.at(0, 0) = D(X001 * F(0.906127f) + X003 * F(-0.318190f) + X005 * F(0.212608f) + X007 * F(-0.180240f));
        Q.at(0, 1) = X002;
        Q.at(0, 2) = D(X001 * F(-0.074658f) + X003 * F(0.513280f) + X005 * F(0.768178f) + X007 * F(-0.375330f));
        Q.at(0, 3) = X006;
        Q.at(1, 0) = D(X011 * F(0.906127f) + X013 * F(-0.318190f) + X015 * F(0.212608f) + X017 * F(-0.180240f));
        Q.at(1, 1) = X012;
        Q.at(1, 2) = D(X011 * F(-0.074658f) + X013 * F(0.513280f) + X015 * F(0.768178f) + X017 * F(-0.375330f));
        Q.at(1, 3) = X016;
        Q.at(2, 0) = D(X021 * F(0.906127f) + X023 * F(-0.318190f) + X025 * F(0.212608f) + X027 * F(-0.180240f));
        Q.at(2, 1) = X022;
        Q.at(2, 2) = D(X021 * F(-0.074658f) + X023 * F(0.513280f) + X025 * F(0.768178f) + X027 * F(-0.375330f));
        Q.at(2, 3) = X026;
        Q.at(3, 0) = D(X031 * F(0.906127f) + X033 * F(-0.318190f) + X035 * F(0.212608f) + X037 * F(-0.180240f));
        Q.at(3, 1) = X032;
        Q.at(3, 2) = D(X031 * F(-0.074658f) + X033 * F(0.513280f) + X035 * F(0.768178f) + X037 * F(-0.375330f));
        Q.at(3, 3) = X036;
        // 40 muls 24 adds
      }
    };
  
    template<int NUM_ROWS, int NUM_COLS>
    struct R_S
    {
      static void calc(Matrix44& R, Matrix44& S, const jpgd_block_t* pSrc)
      {
        // 4x8 = 4x8 times 8x8, matrix 0 is constant
        const Temp_Type X100 = D(F(0.906127f) * AT(1, 0) + F(-0.318190f) * AT(3, 0) + F(0.212608f) * AT(5, 0) + F(-0.180240f) * AT(7, 0));
        const Temp_Type X101 = D(F(0.906127f) * AT(1, 1) + F(-0.318190f) * AT(3, 1) + F(0.212608f) * AT(5, 1) + F(-0.180240f) * AT(7, 1));
        const Temp_Type X102 = D(F(0.906127f) * AT(1, 2) + F(-0.318190f) * AT(3, 2) + F(0.212608f) * AT(5, 2) + F(-0.180240f) * AT(7, 2));
        const Temp_Type X103 = D(F(0.906127f) * AT(1, 3) + F(-0.318190f) * AT(3, 3) + F(0.212608f) * AT(5, 3) + F(-0.180240f) * AT(7, 3));
        const Temp_Type X104 = D(F(0.906127f) * AT(1, 4) + F(-0.318190f) * AT(3, 4) + F(0.212608f) * AT(5, 4) + F(-0.180240f) * AT(7, 4));
        const Temp_Type X105 = D(F(0.906127f) * AT(1, 5) + F(-0.318190f) * AT(3, 5) + F(0.212608f) * AT(5, 5) + F(-0.180240f) * AT(7, 5));
        const Temp_Type X106 = D(F(0.906127f) * AT(1, 6) + F(-0.318190f) * AT(3, 6) + F(0.212608f) * AT(5, 6) + F(-0.180240f) * AT(7, 6));
        const Temp_Type X107 = D(F(0.906127f) * AT(1, 7) + F(-0.318190f) * AT(3, 7) + F(0.212608f) * AT(5, 7) + F(-0.180240f) * AT(7, 7));
        const Temp_Type X110 = AT(2, 0);
        const Temp_Type X111 = AT(2, 1);
        const Temp_Type X112 = AT(2, 2);
        const Temp_Type X113 = AT(2, 3);
        const Temp_Type X114 = AT(2, 4);
        const Temp_Type X115 = AT(2, 5);
        const Temp_Type X116 = AT(2, 6);
        const Temp_Type X117 = AT(2, 7);
        const Temp_Type X120 = D(F(-0.074658f) * AT(1, 0) + F(0.513280f) * AT(3, 0) + F(0.768178f) * AT(5, 0) + F(-0.375330f) * AT(7, 0));
        const Temp_Type X121 = D(F(-0.074658f) * AT(1, 1) + F(0.513280f) * AT(3, 1) + F(0.768178f) * AT(5, 1) + F(-0.375330f) * AT(7, 1));
        const Temp_Type X122 = D(F(-0.074658f) * AT(1, 2) + F(0.513280f) * AT(3, 2) + F(0.768178f) * AT(5, 2) + F(-0.375330f) * AT(7, 2));
        const Temp_Type X123 = D(F(-0.074658f) * AT(1, 3) + F(0.513280f) * AT(3, 3) + F(0.768178f) * AT(5, 3) + F(-0.375330f) * AT(7, 3));
        const Temp_Type X124 = D(F(-0.074658f) * AT(1, 4) + F(0.513280f) * AT(3, 4) + F(0.768178f) * AT(5, 4) + F(-0.375330f) * AT(7, 4));
        const Temp_Type X125 = D(F(-0.074658f) * AT(1, 5) + F(0.513280f) * AT(3, 5) + F(0.768178f) * AT(5, 5) + F(-0.375330f) * AT(7, 5));
        const Temp_Type X126 = D(F(-0.074658f) * AT(1, 6) + F(0.513280f) * AT(3, 6) + F(0.768178f) * AT(5, 6) + F(-0.375330f) * AT(7, 6));
        const Temp_Type X127 = D(F(-0.074658f) * AT(1, 7) + F(0.513280f) * AT(3, 7) + F(0.768178f) * AT(5, 7) + F(-0.375330f) * AT(7, 7));
        const Temp_Type X130 = AT(6, 0);
        const Temp_Type X131 = AT(6, 1);
        const Temp_Type X132 = AT(6, 2);
        const Temp_Type X133 = AT(6, 3);
        const Temp_Type X134 = AT(6, 4);
        const Temp_Type X135 = AT(6, 5);
        const Temp_Type X136 = AT(6, 6);
        const Temp_Type X137 = AT(6, 7);
        // 80 muls 48 adds
  
        // 4x4 = 4x8 times 8x4, matrix 1 is constant
        R.at(0, 0) = X100;
        R.at(0, 1) = D(X101 * F(0.415735f) + X103 * F(0.791065f) + X105 * F(-0.352443f) + X107 * F(0.277785f));
        R.at(0, 2) = X104;
        R.at(0, 3) = D(X101 * F(0.022887f) + X103 * F(-0.097545f) + X105 * F(0.490393f) + X107 * F(0.865723f));
        R.at(1, 0) = X110;
        R.at(1, 1) = D(X111 * F(0.415735f) + X113 * F(0.791065f) + X115 * F(-0.352443f) + X117 * F(0.277785f));
        R.at(1, 2) = X114;
        R.at(1, 3) = D(X111 * F(0.022887f) + X113 * F(-0.097545f) + X115 * F(0.490393f) + X117 * F(0.865723f));
        R.at(2, 0) = X120;
        R.at(2, 1) = D(X121 * F(0.415735f) + X123 * F(0.791065f) + X125 * F(-0.352443f) + X127 * F(0.277785f));
        R.at(2, 2) = X124;
        R.at(2, 3) = D(X121 * F(0.022887f) + X123 * F(-0.097545f) + X125 * F(0.490393f) + X127 * F(0.865723f));
        R.at(3, 0) = X130;
        R.at(3, 1) = D(X131 * F(0.415735f) + X133 * F(0.791065f) + X135 * F(-0.352443f) + X137 * F(0.277785f));
        R.at(3, 2) = X134;
        R.at(3, 3) = D(X131 * F(0.022887f) + X133 * F(-0.097545f) + X135 * F(0.490393f) + X137 * F(0.865723f));
        // 40 muls 24 adds
        // 4x4 = 4x8 times 8x4, matrix 1 is constant
        S.at(0, 0) = D(X101 * F(0.906127f) + X103 * F(-0.318190f) + X105 * F(0.212608f) + X107 * F(-0.180240f));
        S.at(0, 1) = X102;
        S.at(0, 2) = D(X101 * F(-0.074658f) + X103 * F(0.513280f) + X105 * F(0.768178f) + X107 * F(-0.375330f));
        S.at(0, 3) = X106;
        S.at(1, 0) = D(X111 * F(0.906127f) + X113 * F(-0.318190f) + X115 * F(0.212608f) + X117 * F(-0.180240f));
        S.at(1, 1) = X112;
        S.at(1, 2) = D(X111 * F(-0.074658f) + X113 * F(0.513280f) + X115 * F(0.768178f) + X117 * F(-0.375330f));
        S.at(1, 3) = X116;
        S.at(2, 0) = D(X121 * F(0.906127f) + X123 * F(-0.318190f) + X125 * F(0.212608f) + X127 * F(-0.180240f));
        S.at(2, 1) = X122;
        S.at(2, 2) = D(X121 * F(-0.074658f) + X123 * F(0.513280f) + X125 * F(0.768178f) + X127 * F(-0.375330f));
        S.at(2, 3) = X126;
        S.at(3, 0) = D(X131 * F(0.906127f) + X133 * F(-0.318190f) + X135 * F(0.212608f) + X137 * F(-0.180240f));
        S.at(3, 1) = X132;
        S.at(3, 2) = D(X131 * F(-0.074658f) + X133 * F(0.513280f) + X135 * F(0.768178f) + X137 * F(-0.375330f));
        S.at(3, 3) = X136;
        // 40 muls 24 adds
      }
    };
  } // end namespace DCT_Upsample
  
  // Unconditionally frees all allocated m_blocks.
  void jpeg_decoder::free_all_blocks()
  {
    m_pStream = NULL;
    for (mem_block *b = m_pMem_blocks; b; )
    {
      mem_block *n = b->m_pNext;
      jpgd_free(b);
      b = n;
    }
    m_pMem_blocks = NULL;
  }
  
  // This method handles all errors. It will never return.
  // It could easily be changed to use C++ exceptions.
  JPGD_NORETURN void jpeg_decoder::stop_decoding(jpgd_status status)
  {
    m_error_code = status;
    free_all_blocks();
    longjmp(m_jmp_state, status);
  }
  
  void *jpeg_decoder::alloc(size_t nSize, bool zero)
  {
    nSize = (JPGD_MAX(nSize, 1) + 3) & ~3;
    char *rv = NULL;
    for (mem_block *b = m_pMem_blocks; b; b = b->m_pNext)
    {
      if ((b->m_used_count + nSize) <= b->m_size)
      {
        rv = b->m_data + b->m_used_count;
        b->m_used_count += nSize;
        break;
      }
    }
    if (!rv)
    {
      int capacity = JPGD_MAX(32768 - 256, (nSize + 2047) & ~2047);
      mem_block *b = (mem_block*)jpgd_malloc(sizeof(mem_block) + capacity);
      if (!b) { stop_decoding(JPGD_NOTENOUGHMEM); }
      b->m_pNext = m_pMem_blocks; m_pMem_blocks = b;
      b->m_used_count = nSize;
      b->m_size = capacity;
      rv = b->m_data;
    }
    if (zero) memset(rv, 0, nSize);
    return rv;
  }
  
  void jpeg_decoder::word_clear(void *p, uint16 c, uint n)
  {
    uint8 *pD = (uint8*)p;
    const uint8 l = c & 0xFF, h = (c >> 8) & 0xFF;
    while (n)
    {
      pD[0] = l; pD[1] = h; pD += 2;
      n--;
    }
  }
  
  // Refill the input buffer.
  // This method will sit in a loop until (A) the buffer is full or (B)
  // the stream's read() method reports and end of file condition.
  void jpeg_decoder::prep_in_buffer()
  {
    m_in_buf_left = 0;
    m_pIn_buf_ofs = m_in_buf;
  
    if (m_eof_flag)
      return;
  
    do
    {
      int bytes_read = m_pStream->read(m_in_buf + m_in_buf_left, JPGD_IN_BUF_SIZE - m_in_buf_left, &m_eof_flag);
      if (bytes_read == -1)
        stop_decoding(JPGD_STREAM_READ);
  
      m_in_buf_left += bytes_read;
    } while ((m_in_buf_left < JPGD_IN_BUF_SIZE) && (!m_eof_flag));
  
    m_total_bytes_read += m_in_buf_left;
  
    // Pad the end of the block with M_EOI (prevents the decompressor from going off the rails if the stream is invalid).
    // (This dates way back to when this decompressor was written in C/asm, and the all-asm Huffman decoder did some fancy things to increase perf.)
    word_clear(m_pIn_buf_ofs + m_in_buf_left, 0xD9FF, 64);
  }
  
  // Read a Huffman code table.
  void jpeg_decoder::read_dht_marker()
  {
    int i, index, count;
    uint8 huff_num[17];
    uint8 huff_val[256];
  
    uint num_left = get_bits(16);
  
    if (num_left < 2)
      stop_decoding(JPGD_BAD_DHT_MARKER);
  
    num_left -= 2;
  
    while (num_left)
    {
      index = get_bits(8);
  
      huff_num[0] = 0;
  
      count = 0;
  
      for (i = 1; i <= 16; i++)
      {
        huff_num[i] = static_cast<uint8>(get_bits(8));
        count += huff_num[i];
      }
  
      if (count > 255)
        stop_decoding(JPGD_BAD_DHT_COUNTS);
  
      for (i = 0; i < count; i++)
        huff_val[i] = static_cast<uint8>(get_bits(8));
  
      i = 1 + 16 + count;
  
      if (num_left < (uint)i)
        stop_decoding(JPGD_BAD_DHT_MARKER);
  
      num_left -= i;
  
      if ((index & 0x10) > 0x10)
        stop_decoding(JPGD_BAD_DHT_INDEX);
  
      index = (index & 0x0F) + ((index & 0x10) >> 4) * (JPGD_MAX_HUFF_TABLES >> 1);
  
      if (index >= JPGD_MAX_HUFF_TABLES)
        stop_decoding(JPGD_BAD_DHT_INDEX);
  
      if (!m_huff_num[index])
        m_huff_num[index] = (uint8 *)alloc(17);
  
      if (!m_huff_val[index])
        m_huff_val[index] = (uint8 *)alloc(256);
  
      m_huff_ac[index] = (index & 0x10) != 0;
      memcpy(m_huff_num[index], huff_num, 17);
      memcpy(m_huff_val[index], huff_val, 256);
    }
  }
  
  // Read a quantization table.
  void jpeg_decoder::read_dqt_marker()
  {
    int n, i, prec;
    uint num_left;
    uint temp;
  
    num_left = get_bits(16);
  
    if (num_left < 2)
      stop_decoding(JPGD_BAD_DQT_MARKER);
  
    num_left -= 2;
  
    while (num_left)
    {
      n = get_bits(8);
      prec = n >> 4;
      n &= 0x0F;
  
      if (n >= JPGD_MAX_QUANT_TABLES)
        stop_decoding(JPGD_BAD_DQT_TABLE);
  
      if (!m_quant[n])
        m_quant[n] = (jpgd_quant_t *)alloc(64 * sizeof(jpgd_quant_t));
  
      // read quantization entries, in zag order
      for (i = 0; i < 64; i++)
      {
        temp = get_bits(8);
  
        if (prec)
          temp = (temp << 8) + get_bits(8);
  
  			m_quant[n][i] = static_cast<jpgd_quant_t>(temp);
      }
  
      i = 64 + 1;
  
      if (prec)
        i += 64;
  
      if (num_left < (uint)i)
        stop_decoding(JPGD_BAD_DQT_LENGTH);
  
      num_left -= i;
    }
  }
  
  // Read the start of frame (SOF) marker.
  void jpeg_decoder::read_sof_marker()
  {
    int i;
    uint num_left;
  
    num_left = get_bits(16);
  
    if (get_bits(8) != 8)   /* precision: sorry, only 8-bit precision is supported right now */
      stop_decoding(JPGD_BAD_PRECISION);
  
    m_image_y_size = get_bits(16);
  
    if ((m_image_y_size < 1) || (m_image_y_size > JPGD_MAX_HEIGHT))
      stop_decoding(JPGD_BAD_HEIGHT);
  
    m_image_x_size = get_bits(16);
  
    if ((m_image_x_size < 1) || (m_image_x_size > JPGD_MAX_WIDTH))
      stop_decoding(JPGD_BAD_WIDTH);
  
    m_comps_in_frame = get_bits(8);
  
    if (m_comps_in_frame > JPGD_MAX_COMPONENTS)
      stop_decoding(JPGD_TOO_MANY_COMPONENTS);
  
    if (num_left != (uint)(m_comps_in_frame * 3 + 8))
      stop_decoding(JPGD_BAD_SOF_LENGTH);
  
    for (i = 0; i < m_comps_in_frame; i++)
    {
      m_comp_ident[i]  = get_bits(8);
      m_comp_h_samp[i] = get_bits(4);
      m_comp_v_samp[i] = get_bits(4);
      m_comp_quant[i]  = get_bits(8);
    }
  }
  
  // Used to skip unrecognized markers.
  void jpeg_decoder::skip_variable_marker()
  {
    uint num_left;
  
    num_left = get_bits(16);
  
    if (num_left < 2)
      stop_decoding(JPGD_BAD_VARIABLE_MARKER);
  
    num_left -= 2;
  
    while (num_left)
    {
      get_bits(8);
      num_left--;
    }
  }
  
  // Read a define restart interval (DRI) marker.
  void jpeg_decoder::read_dri_marker()
  {
    if (get_bits(16) != 4)
      stop_decoding(JPGD_BAD_DRI_LENGTH);
  
    m_restart_interval = get_bits(16);
  }
  
  // Read a start of scan (SOS) marker.
  void jpeg_decoder::read_sos_marker()
  {
    uint num_left;
    int i, ci, n, c, cc;
  
    num_left = get_bits(16);
  
    n = get_bits(8);
  
    m_comps_in_scan = n;
  
    num_left -= 3;
  
    if ( (num_left != (uint)(n * 2 + 3)) || (n < 1) || (n > JPGD_MAX_COMPS_IN_SCAN) )
      stop_decoding(JPGD_BAD_SOS_LENGTH);
  
    for (i = 0; i < n; i++)
    {
      cc = get_bits(8);
      c = get_bits(8);
      num_left -= 2;
  
      for (ci = 0; ci < m_comps_in_frame; ci++)
        if (cc == m_comp_ident[ci])
          break;
  
      if (ci >= m_comps_in_frame)
        stop_decoding(JPGD_BAD_SOS_COMP_ID);
  
      m_comp_list[i]    = ci;
      m_comp_dc_tab[ci] = (c >> 4) & 15;
      m_comp_ac_tab[ci] = (c & 15) + (JPGD_MAX_HUFF_TABLES >> 1);
    }
  
    m_spectral_start  = get_bits(8);
    m_spectral_end    = get_bits(8);
    m_successive_high = get_bits(4);
    m_successive_low  = get_bits(4);
  
    if (!m_progressive_flag)
    {
      m_spectral_start = 0;
      m_spectral_end = 63;
    }
  
    num_left -= 3;
  
    while (num_left)                  /* read past whatever is num_left */
    {
      get_bits(8);
      num_left--;
    }
  }
  
  // Finds the next marker.
  int jpeg_decoder::next_marker()
  {
    uint c, bytes;
  
    bytes = 0;
  
    do
    {
      do
      {
        bytes++;
        c = get_bits(8);
      } while (c != 0xFF);
  
      do
      {
        c = get_bits(8);
      } while (c == 0xFF);
  
    } while (c == 0);
  
    // If bytes > 0 here, there where extra bytes before the marker (not good).
  
    return c;
  }
  
  // Process markers. Returns when an SOFx, SOI, EOI, or SOS marker is
  // encountered.
  int jpeg_decoder::process_markers()
  {
    int c;
  
    for ( ; ; )
    {
      c = next_marker();
  
      switch (c)
      {
        case M_SOF0:
        case M_SOF1:
        case M_SOF2:
        case M_SOF3:
        case M_SOF5:
        case M_SOF6:
        case M_SOF7:
  //      case M_JPG:
        case M_SOF9:
        case M_SOF10:
        case M_SOF11:
        case M_SOF13:
        case M_SOF14:
        case M_SOF15:
        case M_SOI:
        case M_EOI:
        case M_SOS:
        {
          return c;
        }
        case M_DHT:
        {
          read_dht_marker();
          break;
        }
        // No arithmitic support - dumb patents!
        case M_DAC:
        {
          stop_decoding(JPGD_NO_ARITHMITIC_SUPPORT);
          break;
        }
        case M_DQT:
        {
          read_dqt_marker();
          break;
        }
        case M_DRI:
        {
          read_dri_marker();
          break;
        }
        //case M_APP0:  /* no need to read the JFIF marker */
  
        case M_JPG:
        case M_RST0:    /* no parameters */
        case M_RST1:
        case M_RST2:
        case M_RST3:
        case M_RST4:
        case M_RST5:
        case M_RST6:
        case M_RST7:
        case M_TEM:
        {
          stop_decoding(JPGD_UNEXPECTED_MARKER);
          break;
        }
        default:    /* must be DNL, DHP, EXP, APPn, JPGn, COM, or RESn or APP0 */
        {
          skip_variable_marker();
          break;
        }
      }
    }
  }
  
  // Finds the start of image (SOI) marker.
  // This code is rather defensive: it only checks the first 512 bytes to avoid
  // false positives.
  void jpeg_decoder::locate_soi_marker()
  {
    uint lastchar, thischar;
    uint bytesleft;
  
    lastchar = get_bits(8);
  
    thischar = get_bits(8);
  
    /* ok if it's a normal JPEG file without a special header */
  
    if ((lastchar == 0xFF) && (thischar == M_SOI))
      return;
  
    bytesleft = 4096; //512;
  
    for ( ; ; )
    {
      if (--bytesleft == 0)
        stop_decoding(JPGD_NOT_JPEG);
  
      lastchar = thischar;
  
      thischar = get_bits(8);
  
      if (lastchar == 0xFF)
      {
        if (thischar == M_SOI)
          break;
        else if (thischar == M_EOI) // get_bits will keep returning M_EOI if we read past the end
          stop_decoding(JPGD_NOT_JPEG);
      }
    }
  
    // Check the next character after marker: if it's not 0xFF, it can't be the start of the next marker, so the file is bad.
    thischar = (m_bit_buf >> 24) & 0xFF;
  
    if (thischar != 0xFF)
      stop_decoding(JPGD_NOT_JPEG);
  }
  
  // Find a start of frame (SOF) marker.
  void jpeg_decoder::locate_sof_marker()
  {
    locate_soi_marker();
  
    int c = process_markers();
  
    switch (c)
    {
      case M_SOF2:
        m_progressive_flag = JPGD_TRUE;
      case M_SOF0:  /* baseline DCT */
      case M_SOF1:  /* extended sequential DCT */
      {
        read_sof_marker();
        break;
      }
      case M_SOF9:  /* Arithmitic coding */
      {
        stop_decoding(JPGD_NO_ARITHMITIC_SUPPORT);
        break;
      }
      default:
      {
        stop_decoding(JPGD_UNSUPPORTED_MARKER);
        break;
      }
    }
  }
  
  // Find a start of scan (SOS) marker.
  int jpeg_decoder::locate_sos_marker()
  {
    int c;
  
    c = process_markers();
  
    if (c == M_EOI)
      return JPGD_FALSE;
    else if (c != M_SOS)
      stop_decoding(JPGD_UNEXPECTED_MARKER);
  
    read_sos_marker();
  
    return JPGD_TRUE;
  }
  
  // Reset everything to default/uninitialized state.
  void jpeg_decoder::init(jpeg_decoder_stream *pStream)
  {
    m_pMem_blocks = NULL;
    m_error_code = JPGD_SUCCESS;
    m_ready_flag = false;
    m_image_x_size = m_image_y_size = 0;
    m_pStream = pStream;
    m_progressive_flag = JPGD_FALSE;
  
    memset(m_huff_ac, 0, sizeof(m_huff_ac));
    memset(m_huff_num, 0, sizeof(m_huff_num));
    memset(m_huff_val, 0, sizeof(m_huff_val));
    memset(m_quant, 0, sizeof(m_quant));
  
    m_scan_type = 0;
    m_comps_in_frame = 0;
  
    memset(m_comp_h_samp, 0, sizeof(m_comp_h_samp));
    memset(m_comp_v_samp, 0, sizeof(m_comp_v_samp));
    memset(m_comp_quant, 0, sizeof(m_comp_quant));
    memset(m_comp_ident, 0, sizeof(m_comp_ident));
    memset(m_comp_h_blocks, 0, sizeof(m_comp_h_blocks));
    memset(m_comp_v_blocks, 0, sizeof(m_comp_v_blocks));
  
    m_comps_in_scan = 0;
    memset(m_comp_list, 0, sizeof(m_comp_list));
    memset(m_comp_dc_tab, 0, sizeof(m_comp_dc_tab));
    memset(m_comp_ac_tab, 0, sizeof(m_comp_ac_tab));
  
    m_spectral_start = 0;
    m_spectral_end = 0;
    m_successive_low = 0;
    m_successive_high = 0;
    m_max_mcu_x_size = 0;
    m_max_mcu_y_size = 0;
    m_blocks_per_mcu = 0;
    m_max_blocks_per_row = 0;
    m_mcus_per_row = 0;
    m_mcus_per_col = 0;
    m_expanded_blocks_per_component = 0;
    m_expanded_blocks_per_mcu = 0;
    m_expanded_blocks_per_row = 0;
    m_freq_domain_chroma_upsample = false;
  
    memset(m_mcu_org, 0, sizeof(m_mcu_org));
  
    m_total_lines_left = 0;
    m_mcu_lines_left = 0;
    m_real_dest_bytes_per_scan_line = 0;
    m_dest_bytes_per_scan_line = 0;
    m_dest_bytes_per_pixel = 0;
  
    memset(m_pHuff_tabs, 0, sizeof(m_pHuff_tabs));
  
    memset(m_dc_coeffs, 0, sizeof(m_dc_coeffs));
    memset(m_ac_coeffs, 0, sizeof(m_ac_coeffs));
    memset(m_block_y_mcu, 0, sizeof(m_block_y_mcu));
  
    m_eob_run = 0;
  
    memset(m_block_y_mcu, 0, sizeof(m_block_y_mcu));
  
    m_pIn_buf_ofs = m_in_buf;
    m_in_buf_left = 0;
    m_eof_flag = false;
    m_tem_flag = 0;
  
    memset(m_in_buf_pad_start, 0, sizeof(m_in_buf_pad_start));
    memset(m_in_buf, 0, sizeof(m_in_buf));
    memset(m_in_buf_pad_end, 0, sizeof(m_in_buf_pad_end));
  
    m_restart_interval = 0;
    m_restarts_left    = 0;
    m_next_restart_num = 0;
  
    m_max_mcus_per_row = 0;
    m_max_blocks_per_mcu = 0;
    m_max_mcus_per_col = 0;
  
    memset(m_last_dc_val, 0, sizeof(m_last_dc_val));
    m_pMCU_coefficients = NULL;
    m_pSample_buf = NULL;
  
    m_total_bytes_read = 0;
  
    m_pScan_line_0 = NULL;
    m_pScan_line_1 = NULL;
  
    // Ready the input buffer.
    prep_in_buffer();
  
    // Prime the bit buffer.
    m_bits_left = 16;
    m_bit_buf = 0;
  
    get_bits(16);
    get_bits(16);
  
    for (int i = 0; i < JPGD_MAX_BLOCKS_PER_MCU; i++)
      m_mcu_block_max_zag[i] = 64;
  }
  
  #define SCALEBITS 16
  #define ONE_HALF  ((int) 1 << (SCALEBITS-1))
  #define FIX(x)    ((int) ((x) * (1L<<SCALEBITS) + 0.5f))
  
  // Create a few tables that allow us to quickly convert YCbCr to RGB.
  void jpeg_decoder::create_look_ups()
  {
    for (int i = 0; i <= 255; i++)
    {
      int k = i - 128;
      m_crr[i] = ( FIX(1.40200f)  * k + ONE_HALF) >> SCALEBITS;
      m_cbb[i] = ( FIX(1.77200f)  * k + ONE_HALF) >> SCALEBITS;
      m_crg[i] = (-FIX(0.71414f)) * k;
      m_cbg[i] = (-FIX(0.34414f)) * k + ONE_HALF;
    }
  }
  
  // This method throws back into the stream any bytes that where read
  // into the bit buffer during initial marker scanning.
  void jpeg_decoder::fix_in_buffer()
  {
    // In case any 0xFF's where pulled into the buffer during marker scanning.
    JPGD_ASSERT((m_bits_left & 7) == 0);
  
    if (m_bits_left == 16)
      stuff_char( (uint8)(m_bit_buf & 0xFF));
  
    if (m_bits_left >= 8)
      stuff_char( (uint8)((m_bit_buf >> 8) & 0xFF));
  
    stuff_char((uint8)((m_bit_buf >> 16) & 0xFF));
    stuff_char((uint8)((m_bit_buf >> 24) & 0xFF));
  
    m_bits_left = 16;
    get_bits_no_markers(16);
    get_bits_no_markers(16);
  }
  
  void jpeg_decoder::transform_mcu(int mcu_row)
  {
    jpgd_block_t* pSrc_ptr = m_pMCU_coefficients;
    uint8* pDst_ptr = m_pSample_buf + mcu_row * m_blocks_per_mcu * 64;
  
    for (int mcu_block = 0; mcu_block < m_blocks_per_mcu; mcu_block++)
    {
      idct(pSrc_ptr, pDst_ptr, m_mcu_block_max_zag[mcu_block]);
      pSrc_ptr += 64;
      pDst_ptr += 64;
    }
  }
  
  static const uint8 s_max_rc[64] =
  {
    17, 18, 34, 50, 50, 51, 52, 52, 52, 68, 84, 84, 84, 84, 85, 86, 86, 86, 86, 86,
    102, 118, 118, 118, 118, 118, 118, 119, 120, 120, 120, 120, 120, 120, 120, 136,
    136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136,
    136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136, 136
  };
  
  void jpeg_decoder::transform_mcu_expand(int mcu_row)
  {
    jpgd_block_t* pSrc_ptr = m_pMCU_coefficients;
    uint8* pDst_ptr = m_pSample_buf + mcu_row * m_expanded_blocks_per_mcu * 64;
  
    // Y IDCT
  	int mcu_block;
    for (mcu_block = 0; mcu_block < m_expanded_blocks_per_component; mcu_block++)
    {
      idct(pSrc_ptr, pDst_ptr, m_mcu_block_max_zag[mcu_block]);
      pSrc_ptr += 64;
      pDst_ptr += 64;
    }
  
    // Chroma IDCT, with upsampling
  	jpgd_block_t temp_block[64];
  
    for (int i = 0; i < 2; i++)
    {
      DCT_Upsample::Matrix44 P, Q, R, S;
  
      JPGD_ASSERT(m_mcu_block_max_zag[mcu_block] >= 1);
      JPGD_ASSERT(m_mcu_block_max_zag[mcu_block] <= 64);
  
      int max_zag = m_mcu_block_max_zag[mcu_block++] - 1; 
      if (max_zag <= 0) max_zag = 0; // should never happen, only here to shut up static analysis
      switch (s_max_rc[max_zag])
      {
      case 1*16+1:
        DCT_Upsample::P_Q<1, 1>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<1, 1>::calc(R, S, pSrc_ptr);
        break;
      case 1*16+2:
        DCT_Upsample::P_Q<1, 2>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<1, 2>::calc(R, S, pSrc_ptr);
        break;
      case 2*16+2:
        DCT_Upsample::P_Q<2, 2>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<2, 2>::calc(R, S, pSrc_ptr);
        break;
      case 3*16+2:
        DCT_Upsample::P_Q<3, 2>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<3, 2>::calc(R, S, pSrc_ptr);
        break;
      case 3*16+3:
        DCT_Upsample::P_Q<3, 3>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<3, 3>::calc(R, S, pSrc_ptr);
        break;
      case 3*16+4:
        DCT_Upsample::P_Q<3, 4>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<3, 4>::calc(R, S, pSrc_ptr);
        break;
      case 4*16+4:
        DCT_Upsample::P_Q<4, 4>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<4, 4>::calc(R, S, pSrc_ptr);
        break;
      case 5*16+4:
        DCT_Upsample::P_Q<5, 4>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<5, 4>::calc(R, S, pSrc_ptr);
        break;
      case 5*16+5:
        DCT_Upsample::P_Q<5, 5>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<5, 5>::calc(R, S, pSrc_ptr);
        break;
      case 5*16+6:
        DCT_Upsample::P_Q<5, 6>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<5, 6>::calc(R, S, pSrc_ptr);
        break;
      case 6*16+6:
        DCT_Upsample::P_Q<6, 6>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<6, 6>::calc(R, S, pSrc_ptr);
        break;
      case 7*16+6:
        DCT_Upsample::P_Q<7, 6>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<7, 6>::calc(R, S, pSrc_ptr);
        break;
      case 7*16+7:
        DCT_Upsample::P_Q<7, 7>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<7, 7>::calc(R, S, pSrc_ptr);
        break;
      case 7*16+8:
        DCT_Upsample::P_Q<7, 8>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<7, 8>::calc(R, S, pSrc_ptr);
        break;
      case 8*16+8:
        DCT_Upsample::P_Q<8, 8>::calc(P, Q, pSrc_ptr);
        DCT_Upsample::R_S<8, 8>::calc(R, S, pSrc_ptr);
        break;
      default:
        JPGD_ASSERT(false);
      }
  
      DCT_Upsample::Matrix44 a(P + Q); P -= Q;
      DCT_Upsample::Matrix44& b = P;
      DCT_Upsample::Matrix44 c(R + S); R -= S;
      DCT_Upsample::Matrix44& d = R;
  
      DCT_Upsample::Matrix44::add_and_store(temp_block, a, c);
      idct_4x4(temp_block, pDst_ptr);
      pDst_ptr += 64;
  
      DCT_Upsample::Matrix44::sub_and_store(temp_block, a, c);
      idct_4x4(temp_block, pDst_ptr);
      pDst_ptr += 64;
  
      DCT_Upsample::Matrix44::add_and_store(temp_block, b, d);
      idct_4x4(temp_block, pDst_ptr);
      pDst_ptr += 64;
  
      DCT_Upsample::Matrix44::sub_and_store(temp_block, b, d);
      idct_4x4(temp_block, pDst_ptr);
      pDst_ptr += 64;
  
      pSrc_ptr += 64;
    }
  }
  
  // Loads and dequantizes the next row of (already decoded) coefficients.
  // Progressive images only.
  void jpeg_decoder::load_next_row()
  {
    int i;
    jpgd_block_t *p;
    jpgd_quant_t *q;
    int mcu_row, mcu_block, row_block = 0;
    int component_num, component_id;
    int block_x_mcu[JPGD_MAX_COMPONENTS];
  
    memset(block_x_mcu, 0, JPGD_MAX_COMPONENTS * sizeof(int));
  
    for (mcu_row = 0; mcu_row < m_mcus_per_row; mcu_row++)
    {
      int block_x_mcu_ofs = 0, block_y_mcu_ofs = 0;
  
      for (mcu_block = 0; mcu_block < m_blocks_per_mcu; mcu_block++)
      {
        component_id = m_mcu_org[mcu_block];
        q = m_quant[m_comp_quant[component_id]];
  
        p = m_pMCU_coefficients + 64 * mcu_block;
  
        jpgd_block_t* pAC = coeff_buf_getp(m_ac_coeffs[component_id], block_x_mcu[component_id] + block_x_mcu_ofs, m_block_y_mcu[component_id] + block_y_mcu_ofs);
        jpgd_block_t* pDC = coeff_buf_getp(m_dc_coeffs[component_id], block_x_mcu[component_id] + block_x_mcu_ofs, m_block_y_mcu[component_id] + block_y_mcu_ofs);
        p[0] = pDC[0];
        memcpy(&p[1], &pAC[1], 63 * sizeof(jpgd_block_t));
  
        for (i = 63; i > 0; i--)
          if (p[g_ZAG[i]])
            break;
  
        m_mcu_block_max_zag[mcu_block] = i + 1;
  
        for ( ; i >= 0; i--)
  				if (p[g_ZAG[i]])
  					p[g_ZAG[i]] = static_cast<jpgd_block_t>(p[g_ZAG[i]] * q[i]);
  
        row_block++;
  
        if (m_comps_in_scan == 1)
          block_x_mcu[component_id]++;
        else
        {
          if (++block_x_mcu_ofs == m_comp_h_samp[component_id])
          {
            block_x_mcu_ofs = 0;
  
            if (++block_y_mcu_ofs == m_comp_v_samp[component_id])
            {
              block_y_mcu_ofs = 0;
  
              block_x_mcu[component_id] += m_comp_h_samp[component_id];
            }
          }
        }
      }
  
      if (m_freq_domain_chroma_upsample)
        transform_mcu_expand(mcu_row);
      else
        transform_mcu(mcu_row);
    }
  
    if (m_comps_in_scan == 1)
      m_block_y_mcu[m_comp_list[0]]++;
    else
    {
      for (component_num = 0; component_num < m_comps_in_scan; component_num++)
      {
        component_id = m_comp_list[component_num];
  
        m_block_y_mcu[component_id] += m_comp_v_samp[component_id];
      }
    }
  }
  
  // Restart interval processing.
  void jpeg_decoder::process_restart()
  {
    int i;
    int c = 0;
  
    // Align to a byte boundry
    // FIXME: Is this really necessary? get_bits_no_markers() never reads in markers!
    //get_bits_no_markers(m_bits_left & 7);
  
    // Let's scan a little bit to find the marker, but not _too_ far.
    // 1536 is a "fudge factor" that determines how much to scan.
    for (i = 1536; i > 0; i--)
      if (get_char() == 0xFF)
        break;
  
    if (i == 0)
      stop_decoding(JPGD_BAD_RESTART_MARKER);
  
    for ( ; i > 0; i--)
      if ((c = get_char()) != 0xFF)
        break;
  
    if (i == 0)
      stop_decoding(JPGD_BAD_RESTART_MARKER);
  
    // Is it the expected marker? If not, something bad happened.
    if (c != (m_next_restart_num + M_RST0))
      stop_decoding(JPGD_BAD_RESTART_MARKER);
  
    // Reset each component's DC prediction values.
    memset(&m_last_dc_val, 0, m_comps_in_frame * sizeof(uint));
  
    m_eob_run = 0;
  
    m_restarts_left = m_restart_interval;
  
    m_next_restart_num = (m_next_restart_num + 1) & 7;
  
    // Get the bit buffer going again...
  
    m_bits_left = 16;
    get_bits_no_markers(16);
    get_bits_no_markers(16);
  }
  
  static inline int dequantize_ac(int c, int q) {	c *= q;	return c; }
  
  // Decodes and dequantizes the next row of coefficients.
  void jpeg_decoder::decode_next_row()
  {
    int row_block = 0;
  
    for (int mcu_row = 0; mcu_row < m_mcus_per_row; mcu_row++)
    {
      if ((m_restart_interval) && (m_restarts_left == 0))
        process_restart();
  
      jpgd_block_t* p = m_pMCU_coefficients;
      for (int mcu_block = 0; mcu_block < m_blocks_per_mcu; mcu_block++, p += 64)
      {
        int component_id = m_mcu_org[mcu_block];
        jpgd_quant_t* q = m_quant[m_comp_quant[component_id]];
  
        int r, s;
        s = huff_decode(m_pHuff_tabs[m_comp_dc_tab[component_id]], r);
        s = JPGD_HUFF_EXTEND(r, s);
  
        m_last_dc_val[component_id] = (s += m_last_dc_val[component_id]);
  
        p[0] = static_cast<jpgd_block_t>(s * q[0]);
  
        int prev_num_set = m_mcu_block_max_zag[mcu_block];
  
        huff_tables *pH = m_pHuff_tabs[m_comp_ac_tab[component_id]];
  
        int k;
        for (k = 1; k < 64; k++)
        {
          int extra_bits;
          s = huff_decode(pH, extra_bits);
  
          r = s >> 4;
          s &= 15;
  
          if (s)
          {
            if (r)
            {
              if ((k + r) > 63)
                stop_decoding(JPGD_DECODE_ERROR);
  
              if (k < prev_num_set)
              {
                int n = JPGD_MIN(r, prev_num_set - k);
                int kt = k;
                while (n--)
                  p[g_ZAG[kt++]] = 0;
              }
  
              k += r;
            }
            
            s = JPGD_HUFF_EXTEND(extra_bits, s);
  
            JPGD_ASSERT(k < 64);
  
            p[g_ZAG[k]] = static_cast<jpgd_block_t>(dequantize_ac(s, q[k])); //s * q[k];
          }
          else
          {
            if (r == 15)
            {
              if ((k + 16) > 64)
                stop_decoding(JPGD_DECODE_ERROR);
  
              if (k < prev_num_set)
              {
                int n = JPGD_MIN(16, prev_num_set - k);
                int kt = k;
                while (n--)
                {
                  JPGD_ASSERT(kt <= 63);
                  p[g_ZAG[kt++]] = 0;
                }
              }
  
              k += 16 - 1; // - 1 because the loop counter is k
              JPGD_ASSERT(p[g_ZAG[k]] == 0);
            }
            else
              break;
          }
        }
  
        if (k < prev_num_set)
        {
          int kt = k;
          while (kt < prev_num_set)
            p[g_ZAG[kt++]] = 0;
        }
  
        m_mcu_block_max_zag[mcu_block] = k;
  
        row_block++;
      }
  
      if (m_freq_domain_chroma_upsample)
        transform_mcu_expand(mcu_row);
      else
        transform_mcu(mcu_row);
  
      m_restarts_left--;
    }
  }
  
  // YCbCr H1V1 (1x1:1:1, 3 m_blocks per MCU) to RGB
  void jpeg_decoder::H1V1Convert()
  {
    int row = m_max_mcu_y_size - m_mcu_lines_left;
    uint8 *d = m_pScan_line_0;
    uint8 *s = m_pSample_buf + row * 8;
  
    for (int i = m_max_mcus_per_row; i > 0; i--)
    {
      for (int j = 0; j < 8; j++)
      {
        int y = s[j];
        int cb = s[64+j];
        int cr = s[128+j];
  
        d[0] = clamp(y + m_crr[cr]);
        d[1] = clamp(y + ((m_crg[cr] + m_cbg[cb]) >> 16));
        d[2] = clamp(y + m_cbb[cb]);
        d[3] = 255;
  
        d += 4;
      }
  
      s += 64*3;
    }
  }
  
  // YCbCr H2V1 (2x1:1:1, 4 m_blocks per MCU) to RGB
  void jpeg_decoder::H2V1Convert()
  {
    int row = m_max_mcu_y_size - m_mcu_lines_left;
    uint8 *d0 = m_pScan_line_0;
    uint8 *y = m_pSample_buf + row * 8;
    uint8 *c = m_pSample_buf + 2*64 + row * 8;
  
    for (int i = m_max_mcus_per_row; i > 0; i--)
    {
      for (int l = 0; l < 2; l++)
      {
        for (int j = 0; j < 4; j++)
        {
          int cb = c[0];
          int cr = c[64];
  
          int rc = m_crr[cr];
          int gc = ((m_crg[cr] + m_cbg[cb]) >> 16);
          int bc = m_cbb[cb];
  
          int yy = y[j<<1];
          d0[0] = clamp(yy+rc);
          d0[1] = clamp(yy+gc);
          d0[2] = clamp(yy+bc);
          d0[3] = 255;
  
          yy = y[(j<<1)+1];
          d0[4] = clamp(yy+rc);
          d0[5] = clamp(yy+gc);
          d0[6] = clamp(yy+bc);
          d0[7] = 255;
  
          d0 += 8;
  
          c++;
        }
        y += 64;
      }
  
      y += 64*4 - 64*2;
      c += 64*4 - 8;
    }
  }
  
  // YCbCr H2V1 (1x2:1:1, 4 m_blocks per MCU) to RGB
  void jpeg_decoder::H1V2Convert()
  {
    int row = m_max_mcu_y_size - m_mcu_lines_left;
    uint8 *d0 = m_pScan_line_0;
    uint8 *d1 = m_pScan_line_1;
    uint8 *y;
    uint8 *c;
  
    if (row < 8)
      y = m_pSample_buf + row * 8;
    else
      y = m_pSample_buf + 64*1 + (row & 7) * 8;
  
    c = m_pSample_buf + 64*2 + (row >> 1) * 8;
  
    for (int i = m_max_mcus_per_row; i > 0; i--)
    {
      for (int j = 0; j < 8; j++)
      {
        int cb = c[0+j];
        int cr = c[64+j];
  
        int rc = m_crr[cr];
        int gc = ((m_crg[cr] + m_cbg[cb]) >> 16);
        int bc = m_cbb[cb];
  
        int yy = y[j];
        d0[0] = clamp(yy+rc);
        d0[1] = clamp(yy+gc);
        d0[2] = clamp(yy+bc);
        d0[3] = 255;
  
        yy = y[8+j];
        d1[0] = clamp(yy+rc);
        d1[1] = clamp(yy+gc);
        d1[2] = clamp(yy+bc);
        d1[3] = 255;
  
        d0 += 4;
        d1 += 4;
      }
  
      y += 64*4;
      c += 64*4;
    }
  }
  
  // YCbCr H2V2 (2x2:1:1, 6 m_blocks per MCU) to RGB
  void jpeg_decoder::H2V2Convert()
  {
  	int row = m_max_mcu_y_size - m_mcu_lines_left;
  	uint8 *d0 = m_pScan_line_0;
  	uint8 *d1 = m_pScan_line_1;
  	uint8 *y;
  	uint8 *c;
  
  	if (row < 8)
  		y = m_pSample_buf + row * 8;
  	else
  		y = m_pSample_buf + 64*2 + (row & 7) * 8;
  
  	c = m_pSample_buf + 64*4 + (row >> 1) * 8;
  
  	for (int i = m_max_mcus_per_row; i > 0; i--)
  	{
  		for (int l = 0; l < 2; l++)
  		{
  			for (int j = 0; j < 8; j += 2)
  			{
  				int cb = c[0];
  				int cr = c[64];
  
  				int rc = m_crr[cr];
  				int gc = ((m_crg[cr] + m_cbg[cb]) >> 16);
  				int bc = m_cbb[cb];
  
  				int yy = y[j];
  				d0[0] = clamp(yy+rc);
  				d0[1] = clamp(yy+gc);
  				d0[2] = clamp(yy+bc);
  				d0[3] = 255;
  
  				yy = y[j+1];
  				d0[4] = clamp(yy+rc);
  				d0[5] = clamp(yy+gc);
  				d0[6] = clamp(yy+bc);
  				d0[7] = 255;
  
  				yy = y[j+8];
  				d1[0] = clamp(yy+rc);
  				d1[1] = clamp(yy+gc);
  				d1[2] = clamp(yy+bc);
  				d1[3] = 255;
  
  				yy = y[j+8+1];
  				d1[4] = clamp(yy+rc);
  				d1[5] = clamp(yy+gc);
  				d1[6] = clamp(yy+bc);
  				d1[7] = 255;
  
  				d0 += 8;
  				d1 += 8;
  
  				c++;
  			}
  			y += 64;
  		}
  
  		y += 64*6 - 64*2;
  		c += 64*6 - 8;
  	}
  }
  
  // Y (1 block per MCU) to 8-bit grayscale
  void jpeg_decoder::gray_convert()
  {
    int row = m_max_mcu_y_size - m_mcu_lines_left;
    uint8 *d = m_pScan_line_0;
    uint8 *s = m_pSample_buf + row * 8;
  
    for (int i = m_max_mcus_per_row; i > 0; i--)
    {
      *(uint *)d = *(uint *)s;
      *(uint *)(&d[4]) = *(uint *)(&s[4]);
  
      s += 64;
      d += 8;
    }
  }
  
  void jpeg_decoder::expanded_convert()
  {
    int row = m_max_mcu_y_size - m_mcu_lines_left;
  
    uint8* Py = m_pSample_buf + (row / 8) * 64 * m_comp_h_samp[0] + (row & 7) * 8;
  
    uint8* d = m_pScan_line_0;
  
    for (int i = m_max_mcus_per_row; i > 0; i--)
    {
      for (int k = 0; k < m_max_mcu_x_size; k += 8)
      {
        const int Y_ofs = k * 8;
        const int Cb_ofs = Y_ofs + 64 * m_expanded_blocks_per_component;
        const int Cr_ofs = Y_ofs + 64 * m_expanded_blocks_per_component * 2;
        for (int j = 0; j < 8; j++)
        {
          int y = Py[Y_ofs + j];
          int cb = Py[Cb_ofs + j];
          int cr = Py[Cr_ofs + j];
  
          d[0] = clamp(y + m_crr[cr]);
          d[1] = clamp(y + ((m_crg[cr] + m_cbg[cb]) >> 16));
          d[2] = clamp(y + m_cbb[cb]);
          d[3] = 255;
  
          d += 4;
        }
      }
  
      Py += 64 * m_expanded_blocks_per_mcu;
    }
  }
  
  // Find end of image (EOI) marker, so we can return to the user the exact size of the input stream.
  void jpeg_decoder::find_eoi()
  {
    if (!m_progressive_flag)
    {
      // Attempt to read the EOI marker.
      //get_bits_no_markers(m_bits_left & 7);
  
      // Prime the bit buffer
      m_bits_left = 16;
      get_bits(16);
      get_bits(16);
  
      // The next marker _should_ be EOI
      process_markers();
    }
  
    m_total_bytes_read -= m_in_buf_left;
  }
  
  int jpeg_decoder::decode(const void** pScan_line, uint* pScan_line_len)
  {
    if ((m_error_code) || (!m_ready_flag))
      return JPGD_FAILED;
  
    if (m_total_lines_left == 0)
      return JPGD_DONE;
  
    if (m_mcu_lines_left == 0)
    {
      if (setjmp(m_jmp_state))
        return JPGD_FAILED;
  
      if (m_progressive_flag)
        load_next_row();
      else
        decode_next_row();
  
      // Find the EOI marker if that was the last row.
      if (m_total_lines_left <= m_max_mcu_y_size)
        find_eoi();
  
      m_mcu_lines_left = m_max_mcu_y_size;
    }
  
    if (m_freq_domain_chroma_upsample)
    {
      expanded_convert();
      *pScan_line = m_pScan_line_0;
    }
    else
    {
      switch (m_scan_type)
      {
        case JPGD_YH2V2:
        {
          if ((m_mcu_lines_left & 1) == 0)
          {
            H2V2Convert();
            *pScan_line = m_pScan_line_0;
          }
          else
            *pScan_line = m_pScan_line_1;
  
          break;
        }
        case JPGD_YH2V1:
        {
          H2V1Convert();
          *pScan_line = m_pScan_line_0;
          break;
        }
        case JPGD_YH1V2:
        {
          if ((m_mcu_lines_left & 1) == 0)
          {
            H1V2Convert();
            *pScan_line = m_pScan_line_0;
          }
          else
            *pScan_line = m_pScan_line_1;
  
          break;
        }
        case JPGD_YH1V1:
        {
          H1V1Convert();
          *pScan_line = m_pScan_line_0;
          break;
        }
        case JPGD_GRAYSCALE:
        {
          gray_convert();
          *pScan_line = m_pScan_line_0;
  
          break;
        }
      }
    }
  
    *pScan_line_len = m_real_dest_bytes_per_scan_line;
  
    m_mcu_lines_left--;
    m_total_lines_left--;
  
    return JPGD_SUCCESS;
  }
  
  // Creates the tables needed for efficient Huffman decoding.
  void jpeg_decoder::make_huff_table(int index, huff_tables *pH)
  {
    int p, i, l, si;
    uint8 huffsize[257];
    uint huffcode[257];
    uint code;
    uint subtree;
    int code_size;
    int lastp;
    int nextfreeentry;
    int currententry;
  
    pH->ac_table = m_huff_ac[index] != 0;
  
    p = 0;
  
    for (l = 1; l <= 16; l++)
    {
      for (i = 1; i <= m_huff_num[index][l]; i++)
        huffsize[p++] = static_cast<uint8>(l);
    }
  
    huffsize[p] = 0;
  
    lastp = p;
  
    code = 0;
    si = huffsize[0];
    p = 0;
  
    while (huffsize[p])
    {
      while (huffsize[p] == si)
      {
        huffcode[p++] = code;
        code++;
      }
  
      code <<= 1;
      si++;
    }
  
    memset(pH->look_up, 0, sizeof(pH->look_up));
    memset(pH->look_up2, 0, sizeof(pH->look_up2));
    memset(pH->tree, 0, sizeof(pH->tree));
    memset(pH->code_size, 0, sizeof(pH->code_size));
  
    nextfreeentry = -1;
  
    p = 0;
  
    while (p < lastp)
    {
      i = m_huff_val[index][p];
      code = huffcode[p];
      code_size = huffsize[p];
  
      pH->code_size[i] = static_cast<uint8>(code_size);
  
      if (code_size <= 8)
      {
        code <<= (8 - code_size);
  
        for (l = 1 << (8 - code_size); l > 0; l--)
        {
          JPGD_ASSERT(i < 256);
  
          pH->look_up[code] = i;
  
          bool has_extrabits = false;
  				int extra_bits = 0;
          int num_extra_bits = i & 15;
  
          int bits_to_fetch = code_size;
          if (num_extra_bits)
          {
            int total_codesize = code_size + num_extra_bits;
            if (total_codesize <= 8)
            {
              has_extrabits = true;
              extra_bits = ((1 << num_extra_bits) - 1) & (code >> (8 - total_codesize));
              JPGD_ASSERT(extra_bits <= 0x7FFF);
              bits_to_fetch += num_extra_bits;
            }
          }
  
          if (!has_extrabits)
            pH->look_up2[code] = i | (bits_to_fetch << 8);
          else
            pH->look_up2[code] = i | 0x8000 | (extra_bits << 16) | (bits_to_fetch << 8);
  
          code++;
        }
      }
      else
      {
        subtree = (code >> (code_size - 8)) & 0xFF;
  
        currententry = pH->look_up[subtree];
  
        if (currententry == 0)
        {
          pH->look_up[subtree] = currententry = nextfreeentry;
          pH->look_up2[subtree] = currententry = nextfreeentry;
  
          nextfreeentry -= 2;
        }
  
        code <<= (16 - (code_size - 8));
  
        for (l = code_size; l > 9; l--)
        {
          if ((code & 0x8000) == 0)
            currententry--;
  
          if (pH->tree[-currententry - 1] == 0)
          {
            pH->tree[-currententry - 1] = nextfreeentry;
  
            currententry = nextfreeentry;
  
            nextfreeentry -= 2;
          }
          else
            currententry = pH->tree[-currententry - 1];
  
          code <<= 1;
        }
  
        if ((code & 0x8000) == 0)
          currententry--;
  
        pH->tree[-currententry - 1] = i;
      }
  
      p++;
    }
  }
  
  // Verifies the quantization tables needed for this scan are available.
  void jpeg_decoder::check_quant_tables()
  {
    for (int i = 0; i < m_comps_in_scan; i++)
      if (m_quant[m_comp_quant[m_comp_list[i]]] == NULL)
        stop_decoding(JPGD_UNDEFINED_QUANT_TABLE);
  }
  
  // Verifies that all the Huffman tables needed for this scan are available.
  void jpeg_decoder::check_huff_tables()
  {
    for (int i = 0; i < m_comps_in_scan; i++)
    {
      if ((m_spectral_start == 0) && (m_huff_num[m_comp_dc_tab[m_comp_list[i]]] == NULL))
        stop_decoding(JPGD_UNDEFINED_HUFF_TABLE);
  
      if ((m_spectral_end > 0) && (m_huff_num[m_comp_ac_tab[m_comp_list[i]]] == NULL))
        stop_decoding(JPGD_UNDEFINED_HUFF_TABLE);
    }
  
    for (int i = 0; i < JPGD_MAX_HUFF_TABLES; i++)
      if (m_huff_num[i])
      {
        if (!m_pHuff_tabs[i])
          m_pHuff_tabs[i] = (huff_tables *)alloc(sizeof(huff_tables));
  
        make_huff_table(i, m_pHuff_tabs[i]);
      }
  }
  
  // Determines the component order inside each MCU.
  // Also calcs how many MCU's are on each row, etc.
  void jpeg_decoder::calc_mcu_block_order()
  {
    int component_num, component_id;
    int max_h_samp = 0, max_v_samp = 0;
  
    for (component_id = 0; component_id < m_comps_in_frame; component_id++)
    {
      if (m_comp_h_samp[component_id] > max_h_samp)
        max_h_samp = m_comp_h_samp[component_id];
  
      if (m_comp_v_samp[component_id] > max_v_samp)
        max_v_samp = m_comp_v_samp[component_id];
    }
  
    for (component_id = 0; component_id < m_comps_in_frame; component_id++)
    {
      m_comp_h_blocks[component_id] = ((((m_image_x_size * m_comp_h_samp[component_id]) + (max_h_samp - 1)) / max_h_samp) + 7) / 8;
      m_comp_v_blocks[component_id] = ((((m_image_y_size * m_comp_v_samp[component_id]) + (max_v_samp - 1)) / max_v_samp) + 7) / 8;
    }
  
    if (m_comps_in_scan == 1)
    {
      m_mcus_per_row = m_comp_h_blocks[m_comp_list[0]];
      m_mcus_per_col = m_comp_v_blocks[m_comp_list[0]];
    }
    else
    {
      m_mcus_per_row = (((m_image_x_size + 7) / 8) + (max_h_samp - 1)) / max_h_samp;
      m_mcus_per_col = (((m_image_y_size + 7) / 8) + (max_v_samp - 1)) / max_v_samp;
    }
  
    if (m_comps_in_scan == 1)
    {
      m_mcu_org[0] = m_comp_list[0];
  
      m_blocks_per_mcu = 1;
    }
    else
    {
      m_blocks_per_mcu = 0;
  
      for (component_num = 0; component_num < m_comps_in_scan; component_num++)
      {
        int num_blocks;
  
        component_id = m_comp_list[component_num];
  
        num_blocks = m_comp_h_samp[component_id] * m_comp_v_samp[component_id];
  
        while (num_blocks--)
          m_mcu_org[m_blocks_per_mcu++] = component_id;
      }
    }
  }
  
  // Starts a new scan.
  int jpeg_decoder::init_scan()
  {
    if (!locate_sos_marker())
      return JPGD_FALSE;
  
    calc_mcu_block_order();
  
    check_huff_tables();
  
    check_quant_tables();
  
    memset(m_last_dc_val, 0, m_comps_in_frame * sizeof(uint));
  
    m_eob_run = 0;
  
    if (m_restart_interval)
    {
      m_restarts_left = m_restart_interval;
      m_next_restart_num = 0;
    }
  
    fix_in_buffer();
  
    return JPGD_TRUE;
  }
  
  // Starts a frame. Determines if the number of components or sampling factors
  // are supported.
  void jpeg_decoder::init_frame()
  {
    int i;
  
    if (m_comps_in_frame == 1)
    {
      if ((m_comp_h_samp[0] != 1) || (m_comp_v_samp[0] != 1))
        stop_decoding(JPGD_UNSUPPORTED_SAMP_FACTORS);
  
      m_scan_type = JPGD_GRAYSCALE;
      m_max_blocks_per_mcu = 1;
      m_max_mcu_x_size = 8;
      m_max_mcu_y_size = 8;
    }
    else if (m_comps_in_frame == 3)
    {
      if ( ((m_comp_h_samp[1] != 1) || (m_comp_v_samp[1] != 1)) ||
           ((m_comp_h_samp[2] != 1) || (m_comp_v_samp[2] != 1)) )
        stop_decoding(JPGD_UNSUPPORTED_SAMP_FACTORS);
  
      if ((m_comp_h_samp[0] == 1) && (m_comp_v_samp[0] == 1))
      {
        m_scan_type = JPGD_YH1V1;
  
        m_max_blocks_per_mcu = 3;
        m_max_mcu_x_size = 8;
        m_max_mcu_y_size = 8;
      }
      else if ((m_comp_h_samp[0] == 2) && (m_comp_v_samp[0] == 1))
      {
        m_scan_type = JPGD_YH2V1;
        m_max_blocks_per_mcu = 4;
        m_max_mcu_x_size = 16;
        m_max_mcu_y_size = 8;
      }
      else if ((m_comp_h_samp[0] == 1) && (m_comp_v_samp[0] == 2))
      {
        m_scan_type = JPGD_YH1V2;
        m_max_blocks_per_mcu = 4;
        m_max_mcu_x_size = 8;
        m_max_mcu_y_size = 16;
      }
      else if ((m_comp_h_samp[0] == 2) && (m_comp_v_samp[0] == 2))
      {
        m_scan_type = JPGD_YH2V2;
        m_max_blocks_per_mcu = 6;
        m_max_mcu_x_size = 16;
        m_max_mcu_y_size = 16;
      }
      else
        stop_decoding(JPGD_UNSUPPORTED_SAMP_FACTORS);
    }
    else
      stop_decoding(JPGD_UNSUPPORTED_COLORSPACE);
  
    m_max_mcus_per_row = (m_image_x_size + (m_max_mcu_x_size - 1)) / m_max_mcu_x_size;
    m_max_mcus_per_col = (m_image_y_size + (m_max_mcu_y_size - 1)) / m_max_mcu_y_size;
  
    // These values are for the *destination* pixels: after conversion.
    if (m_scan_type == JPGD_GRAYSCALE)
      m_dest_bytes_per_pixel = 1;
    else
      m_dest_bytes_per_pixel = 4;
  
    m_dest_bytes_per_scan_line = ((m_image_x_size + 15) & 0xFFF0) * m_dest_bytes_per_pixel;
  
    m_real_dest_bytes_per_scan_line = (m_image_x_size * m_dest_bytes_per_pixel);
  
    // Initialize two scan line buffers.
    m_pScan_line_0 = (uint8 *)alloc(m_dest_bytes_per_scan_line, true);
    if ((m_scan_type == JPGD_YH1V2) || (m_scan_type == JPGD_YH2V2))
      m_pScan_line_1 = (uint8 *)alloc(m_dest_bytes_per_scan_line, true);
  
    m_max_blocks_per_row = m_max_mcus_per_row * m_max_blocks_per_mcu;
  
    // Should never happen
    if (m_max_blocks_per_row > JPGD_MAX_BLOCKS_PER_ROW)
      stop_decoding(JPGD_ASSERTION_ERROR);
  
    // Allocate the coefficient buffer, enough for one MCU
    m_pMCU_coefficients = (jpgd_block_t*)alloc(m_max_blocks_per_mcu * 64 * sizeof(jpgd_block_t));
  
    for (i = 0; i < m_max_blocks_per_mcu; i++)
      m_mcu_block_max_zag[i] = 64;
  
    m_expanded_blocks_per_component = m_comp_h_samp[0] * m_comp_v_samp[0];
    m_expanded_blocks_per_mcu = m_expanded_blocks_per_component * m_comps_in_frame;
    m_expanded_blocks_per_row = m_max_mcus_per_row * m_expanded_blocks_per_mcu;
  	// Freq. domain chroma upsampling is only supported for H2V2 subsampling factor (the most common one I've seen).
    m_freq_domain_chroma_upsample = false;
  #if JPGD_SUPPORT_FREQ_DOMAIN_UPSAMPLING
    m_freq_domain_chroma_upsample = (m_expanded_blocks_per_mcu == 4*3);
  #endif
  
    if (m_freq_domain_chroma_upsample)
      m_pSample_buf = (uint8 *)alloc(m_expanded_blocks_per_row * 64);
    else
      m_pSample_buf = (uint8 *)alloc(m_max_blocks_per_row * 64);
  
    m_total_lines_left = m_image_y_size;
  
    m_mcu_lines_left = 0;
  
    create_look_ups();
  }
  
  // The coeff_buf series of methods originally stored the coefficients
  // into a "virtual" file which was located in EMS, XMS, or a disk file. A cache
  // was used to make this process more efficient. Now, we can store the entire
  // thing in RAM.
  jpeg_decoder::coeff_buf* jpeg_decoder::coeff_buf_open(int block_num_x, int block_num_y, int block_len_x, int block_len_y)
  {
    coeff_buf* cb = (coeff_buf*)alloc(sizeof(coeff_buf));
  
    cb->block_num_x = block_num_x;
    cb->block_num_y = block_num_y;
    cb->block_len_x = block_len_x;
    cb->block_len_y = block_len_y;
    cb->block_size = (block_len_x * block_len_y) * sizeof(jpgd_block_t);
    cb->pData = (uint8 *)alloc(cb->block_size * block_num_x * block_num_y, true);
    return cb;
  }
  
  inline jpgd_block_t *jpeg_decoder::coeff_buf_getp(coeff_buf *cb, int block_x, int block_y)
  {
    JPGD_ASSERT((block_x < cb->block_num_x) && (block_y < cb->block_num_y));
    return (jpgd_block_t *)(cb->pData + block_x * cb->block_size + block_y * (cb->block_size * cb->block_num_x));
  }
  
  // The following methods decode the various types of m_blocks encountered
  // in progressively encoded images.
  void jpeg_decoder::decode_block_dc_first(jpeg_decoder *pD, int component_id, int block_x, int block_y)
  {
    int s, r;
    jpgd_block_t *p = pD->coeff_buf_getp(pD->m_dc_coeffs[component_id], block_x, block_y);
  
    if ((s = pD->huff_decode(pD->m_pHuff_tabs[pD->m_comp_dc_tab[component_id]])) != 0)
    {
      r = pD->get_bits_no_markers(s);
      s = JPGD_HUFF_EXTEND(r, s);
    }
  
    pD->m_last_dc_val[component_id] = (s += pD->m_last_dc_val[component_id]);
  
    p[0] = static_cast<jpgd_block_t>(s << pD->m_successive_low);
  }
  
  void jpeg_decoder::decode_block_dc_refine(jpeg_decoder *pD, int component_id, int block_x, int block_y)
  {
    if (pD->get_bits_no_markers(1))
    {
      jpgd_block_t *p = pD->coeff_buf_getp(pD->m_dc_coeffs[component_id], block_x, block_y);
  
      p[0] |= (1 << pD->m_successive_low);
    }
  }
  
  void jpeg_decoder::decode_block_ac_first(jpeg_decoder *pD, int component_id, int block_x, int block_y)
  {
    int k, s, r;
  
    if (pD->m_eob_run)
    {
      pD->m_eob_run--;
      return;
    }
  
    jpgd_block_t *p = pD->coeff_buf_getp(pD->m_ac_coeffs[component_id], block_x, block_y);
  
    for (k = pD->m_spectral_start; k <= pD->m_spectral_end; k++)
    {
      s = pD->huff_decode(pD->m_pHuff_tabs[pD->m_comp_ac_tab[component_id]]);
  
      r = s >> 4;
      s &= 15;
  
      if (s)
      {
        if ((k += r) > 63)
          pD->stop_decoding(JPGD_DECODE_ERROR);
  
        r = pD->get_bits_no_markers(s);
        s = JPGD_HUFF_EXTEND(r, s);
  
        p[g_ZAG[k]] = static_cast<jpgd_block_t>(s << pD->m_successive_low);
      }
      else
      {
        if (r == 15)
        {
          if ((k += 15) > 63)
            pD->stop_decoding(JPGD_DECODE_ERROR);
        }
        else
        {
          pD->m_eob_run = 1 << r;
  
          if (r)
            pD->m_eob_run += pD->get_bits_no_markers(r);
  
          pD->m_eob_run--;
  
          break;
        }
      }
    }
  }
  
  void jpeg_decoder::decode_block_ac_refine(jpeg_decoder *pD, int component_id, int block_x, int block_y)
  {
    int s, k, r;
    int p1 = 1 << pD->m_successive_low;
    int m1 = (-1) << pD->m_successive_low;
    jpgd_block_t *p = pD->coeff_buf_getp(pD->m_ac_coeffs[component_id], block_x, block_y);
    
    JPGD_ASSERT(pD->m_spectral_end <= 63);
    
    k = pD->m_spectral_start;
    
    if (pD->m_eob_run == 0)
    {
      for ( ; k <= pD->m_spectral_end; k++)
      {
        s = pD->huff_decode(pD->m_pHuff_tabs[pD->m_comp_ac_tab[component_id]]);
  
        r = s >> 4;
        s &= 15;
  
        if (s)
        {
          if (s != 1)
            pD->stop_decoding(JPGD_DECODE_ERROR);
  
          if (pD->get_bits_no_markers(1))
            s = p1;
          else
            s = m1;
        }
        else
        {
          if (r != 15)
          {
            pD->m_eob_run = 1 << r;
  
            if (r)
              pD->m_eob_run += pD->get_bits_no_markers(r);
  
            break;
          }
        }
  
        do
        {
          jpgd_block_t *this_coef = p + g_ZAG[k & 63];
  
          if (*this_coef != 0)
          {
            if (pD->get_bits_no_markers(1))
            {
              if ((*this_coef & p1) == 0)
              {
                if (*this_coef >= 0)
                  *this_coef = static_cast<jpgd_block_t>(*this_coef + p1);
                else
                  *this_coef = static_cast<jpgd_block_t>(*this_coef + m1);
              }
            }
          }
          else
          {
            if (--r < 0)
              break;
          }
  
          k++;
  
        } while (k <= pD->m_spectral_end);
  
        if ((s) && (k < 64))
        {
          p[g_ZAG[k]] = static_cast<jpgd_block_t>(s);
        }
      }
    }
  
    if (pD->m_eob_run > 0)
    {
      for ( ; k <= pD->m_spectral_end; k++)
      {
        jpgd_block_t *this_coef = p + g_ZAG[k & 63]; // logical AND to shut up static code analysis
  
        if (*this_coef != 0)
        {
          if (pD->get_bits_no_markers(1))
          {
            if ((*this_coef & p1) == 0)
            {
              if (*this_coef >= 0)
                *this_coef = static_cast<jpgd_block_t>(*this_coef + p1);
              else
                *this_coef = static_cast<jpgd_block_t>(*this_coef + m1);
            }
          }
        }
      }
  
      pD->m_eob_run--;
    }
  }
  
  // Decode a scan in a progressively encoded image.
  void jpeg_decoder::decode_scan(pDecode_block_func decode_block_func)
  {
    int mcu_row, mcu_col, mcu_block;
    int block_x_mcu[JPGD_MAX_COMPONENTS], m_block_y_mcu[JPGD_MAX_COMPONENTS];
  
    memset(m_block_y_mcu, 0, sizeof(m_block_y_mcu));
  
    for (mcu_col = 0; mcu_col < m_mcus_per_col; mcu_col++)
    {
      int component_num, component_id;
  
      memset(block_x_mcu, 0, sizeof(block_x_mcu));
  
      for (mcu_row = 0; mcu_row < m_mcus_per_row; mcu_row++)
      {
        int block_x_mcu_ofs = 0, block_y_mcu_ofs = 0;
  
        if ((m_restart_interval) && (m_restarts_left == 0))
          process_restart();
  
        for (mcu_block = 0; mcu_block < m_blocks_per_mcu; mcu_block++)
        {
          component_id = m_mcu_org[mcu_block];
  
          decode_block_func(this, component_id, block_x_mcu[component_id] + block_x_mcu_ofs, m_block_y_mcu[component_id] + block_y_mcu_ofs);
  
          if (m_comps_in_scan == 1)
            block_x_mcu[component_id]++;
          else
          {
            if (++block_x_mcu_ofs == m_comp_h_samp[component_id])
            {
              block_x_mcu_ofs = 0;
  
              if (++block_y_mcu_ofs == m_comp_v_samp[component_id])
              {
                block_y_mcu_ofs = 0;
                block_x_mcu[component_id] += m_comp_h_samp[component_id];
              }
            }
          }
        }
  
        m_restarts_left--;
      }
  
      if (m_comps_in_scan == 1)
        m_block_y_mcu[m_comp_list[0]]++;
      else
      {
        for (component_num = 0; component_num < m_comps_in_scan; component_num++)
        {
          component_id = m_comp_list[component_num];
          m_block_y_mcu[component_id] += m_comp_v_samp[component_id];
        }
      }
    }
  }
  
  // Decode a progressively encoded image.
  void jpeg_decoder::init_progressive()
  {
    int i;
  
    if (m_comps_in_frame == 4)
      stop_decoding(JPGD_UNSUPPORTED_COLORSPACE);
  
    // Allocate the coefficient buffers.
    for (i = 0; i < m_comps_in_frame; i++)
    {
      m_dc_coeffs[i] = coeff_buf_open(m_max_mcus_per_row * m_comp_h_samp[i], m_max_mcus_per_col * m_comp_v_samp[i], 1, 1);
      m_ac_coeffs[i] = coeff_buf_open(m_max_mcus_per_row * m_comp_h_samp[i], m_max_mcus_per_col * m_comp_v_samp[i], 8, 8);
    }
  
    for ( ; ; )
    {
      int dc_only_scan, refinement_scan;
      pDecode_block_func decode_block_func;
  
      if (!init_scan())
        break;
  
      dc_only_scan = (m_spectral_start == 0);
      refinement_scan = (m_successive_high != 0);
  
      if ((m_spectral_start > m_spectral_end) || (m_spectral_end > 63))
        stop_decoding(JPGD_BAD_SOS_SPECTRAL);
  
      if (dc_only_scan)
      {
        if (m_spectral_end)
          stop_decoding(JPGD_BAD_SOS_SPECTRAL);
      }
      else if (m_comps_in_scan != 1)  /* AC scans can only contain one component */
        stop_decoding(JPGD_BAD_SOS_SPECTRAL);
  
      if ((refinement_scan) && (m_successive_low != m_successive_high - 1))
        stop_decoding(JPGD_BAD_SOS_SUCCESSIVE);
  
      if (dc_only_scan)
      {
        if (refinement_scan)
          decode_block_func = decode_block_dc_refine;
        else
          decode_block_func = decode_block_dc_first;
      }
      else
      {
        if (refinement_scan)
          decode_block_func = decode_block_ac_refine;
        else
          decode_block_func = decode_block_ac_first;
      }
  
      decode_scan(decode_block_func);
  
      m_bits_left = 16;
      get_bits(16);
      get_bits(16);
    }
  
    m_comps_in_scan = m_comps_in_frame;
  
    for (i = 0; i < m_comps_in_frame; i++)
      m_comp_list[i] = i;
  
    calc_mcu_block_order();
  }
  
  void jpeg_decoder::init_sequential()
  {
    if (!init_scan())
      stop_decoding(JPGD_UNEXPECTED_MARKER);
  }
  
  void jpeg_decoder::decode_start()
  {
    init_frame();
  
    if (m_progressive_flag)
      init_progressive();
    else
      init_sequential();
  }
  
  void jpeg_decoder::decode_init(jpeg_decoder_stream *pStream)
  {
    init(pStream);
    locate_sof_marker();
  }
  
  jpeg_decoder::jpeg_decoder(jpeg_decoder_stream *pStream)
  {
    if (setjmp(m_jmp_state))
      return;
    decode_init(pStream);
  }
  
  int jpeg_decoder::begin_decoding()
  {
    if (m_ready_flag)
      return JPGD_SUCCESS;
  
    if (m_error_code)
      return JPGD_FAILED;
  
    if (setjmp(m_jmp_state))
      return JPGD_FAILED;
  
    decode_start();
  
    m_ready_flag = true;
  
    return JPGD_SUCCESS;
  }
  
  jpeg_decoder::~jpeg_decoder()
  {
    free_all_blocks();
  }
  
  jpeg_decoder_file_stream::jpeg_decoder_file_stream()
  {
    m_pFile = NULL;
    m_eof_flag = false;
    m_error_flag = false;
  }
  
  void jpeg_decoder_file_stream::close()
  {
    if (m_pFile)
    {
      fclose(m_pFile);
      m_pFile = NULL;
    }
  
    m_eof_flag = false;
    m_error_flag = false;
  }
  
  jpeg_decoder_file_stream::~jpeg_decoder_file_stream()
  {
    close();
  }
  
  bool jpeg_decoder_file_stream::open(const char *Pfilename)
  {
    close();
  
    m_eof_flag = false;
    m_error_flag = false;
  
  #if defined(_MSC_VER)
    m_pFile = NULL;
    fopen_s(&m_pFile, Pfilename, "rb");
  #else
    m_pFile = fopen(Pfilename, "rb");
  #endif
    return m_pFile != NULL;
  }
  
  int jpeg_decoder_file_stream::read(uint8 *pBuf, int max_bytes_to_read, bool *pEOF_flag)
  {
    if (!m_pFile)
      return -1;
  
    if (m_eof_flag)
    {
      *pEOF_flag = true;
      return 0;
    }
  
    if (m_error_flag)
      return -1;
  
    int bytes_read = static_cast<int>(fread(pBuf, 1, max_bytes_to_read, m_pFile));
    if (bytes_read < max_bytes_to_read)
    {
      if (ferror(m_pFile))
      {
        m_error_flag = true;
        return -1;
      }
  
      m_eof_flag = true;
      *pEOF_flag = true;
    }
  
    return bytes_read;
  }
  
  bool jpeg_decoder_mem_stream::open(const uint8 *pSrc_data, uint size)
  {
    close();
    m_pSrc_data = pSrc_data;
    m_ofs = 0;
    m_size = size;
    return true;
  }
  
  int jpeg_decoder_mem_stream::read(uint8 *pBuf, int max_bytes_to_read, bool *pEOF_flag)
  {
    *pEOF_flag = false;
  
    if (!m_pSrc_data)
      return -1;
  
    uint bytes_remaining = m_size - m_ofs;
    if ((uint)max_bytes_to_read > bytes_remaining)
    {
      max_bytes_to_read = bytes_remaining;
      *pEOF_flag = true;
    }
  
    memcpy(pBuf, m_pSrc_data + m_ofs, max_bytes_to_read);
    m_ofs += max_bytes_to_read;
  
    return max_bytes_to_read;
  }
  
  unsigned char *decompress_jpeg_image_from_stream(jpeg_decoder_stream *pStream, int *width, int *height, int *actual_comps, int req_comps)
  {
    if (!actual_comps)
      return NULL;
    *actual_comps = 0;
  
    if ((!pStream) || (!width) || (!height) || (!req_comps))
      return NULL;
  
    if ((req_comps != 1) && (req_comps != 3) && (req_comps != 4))
      return NULL;
  
    jpeg_decoder decoder(pStream);
    if (decoder.get_error_code() != JPGD_SUCCESS)
      return NULL;
  
    const int image_width = decoder.get_width(), image_height = decoder.get_height();
    *width = image_width;
    *height = image_height;
    *actual_comps = decoder.get_num_components();
  
    if (decoder.begin_decoding() != JPGD_SUCCESS)
      return NULL;
  
    const int dst_bpl = image_width * req_comps;
  
    uint8 *pImage_data = (uint8*)jpgd_malloc(dst_bpl * image_height);
    if (!pImage_data)
      return NULL;
  
    for (int y = 0; y < image_height; y++)
    {
      const uint8* pScan_line = NULL;
      uint scan_line_len;
      if (decoder.decode((const void**)&pScan_line, &scan_line_len) != JPGD_SUCCESS)
      {
        jpgd_free(pImage_data);
        return NULL;
      }
  
      uint8 *pDst = pImage_data + y * dst_bpl;
  
      if (((req_comps == 1) && (decoder.get_num_components() == 1)) || ((req_comps == 4) && (decoder.get_num_components() == 3)))
        memcpy(pDst, pScan_line, dst_bpl);
      else if (decoder.get_num_components() == 1)
      {
        if (req_comps == 3)
        {
          for (int x = 0; x < image_width; x++)
          {
            uint8 luma = pScan_line[x];
            pDst[0] = luma;
            pDst[1] = luma;
            pDst[2] = luma;
            pDst += 3;
          }
        }
        else
        {
          for (int x = 0; x < image_width; x++)
          {
            uint8 luma = pScan_line[x];
            pDst[0] = luma;
            pDst[1] = luma;
            pDst[2] = luma;
            pDst[3] = 255;
            pDst += 4;
          }
        }
      }
      else if (decoder.get_num_components() == 3)
      {
        if (req_comps == 1)
        {
          const int YR = 19595, YG = 38470, YB = 7471;
          for (int x = 0; x < image_width; x++)
          {
            int r = pScan_line[x*4+0];
            int g = pScan_line[x*4+1];
            int b = pScan_line[x*4+2];
            *pDst++ = static_cast<uint8>((r * YR + g * YG + b * YB + 32768) >> 16);
          }
        }
        else
        {
          for (int x = 0; x < image_width; x++)
          {
            pDst[0] = pScan_line[x*4+0];
            pDst[1] = pScan_line[x*4+1];
            pDst[2] = pScan_line[x*4+2];
            pDst += 3;
          }
        }
      }
    }
  
    return pImage_data;
  }
  
  unsigned char *decompress_jpeg_image_from_memory(const unsigned char *pSrc_data, int src_data_size, int *width, int *height, int *actual_comps, int req_comps)
  {
    jpgd::jpeg_decoder_mem_stream mem_stream(pSrc_data, src_data_size);
    return decompress_jpeg_image_from_stream(&mem_stream, width, height, actual_comps, req_comps);
  }
  
  unsigned char *decompress_jpeg_image_from_file(const char *pSrc_filename, int *width, int *height, int *actual_comps, int req_comps)
  {
    jpgd::jpeg_decoder_file_stream file_stream;
    if (!file_stream.open(pSrc_filename))
      return NULL;
    return decompress_jpeg_image_from_stream(&file_stream, width, height, actual_comps, req_comps);
  }
  
  } // namespace jpgd
  