
/* pngtrans.c - transforms the data in a row (used by both readers and writers)
 *
 * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 */

#include "pngpriv.h"
#define PNG_SRC_FILE PNG_SRC_FILE_pngtrans

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)

#if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
/* Turn on BGR-to-RGB mapping */
void PNGAPI
png_set_bgr(png_structrp png_ptr)
{
   png_debug(1, "in png_set_bgr");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_BGR;
}
#endif

#if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
/* Turn on 16 bit byte swapping */
void PNGAPI
png_set_swap(png_structrp png_ptr)
{
   png_debug(1, "in png_set_swap");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth == 16)
      png_ptr->transformations |= PNG_SWAP_BYTES;
}
#endif

#if defined(PNG_READ_PACK_SUPPORTED) || defined(PNG_WRITE_PACK_SUPPORTED)
/* Turn on pixel packing */
void PNGAPI
png_set_packing(png_structrp png_ptr)
{
   png_debug(1, "in png_set_packing");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth < 8)
   {
      png_ptr->transformations |= PNG_PACK;
#     ifdef PNG_WRITE_SUPPORTED
         png_ptr->usr_bit_depth = 8;
#     endif
   }
}
#endif

#if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
/* Turn on packed pixel swapping */
void PNGAPI
png_set_packswap(png_structrp png_ptr)
{
   png_debug(1, "in png_set_packswap");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth < 8)
      png_ptr->transformations |= PNG_PACKSWAP;
}
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED) || defined(PNG_WRITE_SHIFT_SUPPORTED)
void PNGAPI
png_set_shift(png_structrp png_ptr, png_const_color_8p true_bits)
{
   png_debug(1, "in png_set_shift");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_SHIFT;
   png_ptr->shift = *true_bits;
}
#endif

#if defined(PNG_READ_INTERLACING_SUPPORTED) || \
    defined(PNG_WRITE_INTERLACING_SUPPORTED)
int PNGAPI
png_set_interlace_handling(png_structrp png_ptr)
{
   png_debug(1, "in png_set_interlace handling");

   if (png_ptr != 0 && png_ptr->interlaced != 0)
   {
      png_ptr->transformations |= PNG_INTERLACE;
      return (7);
   }

   return (1);
}
#endif

#if defined(PNG_READ_FILLER_SUPPORTED) || defined(PNG_WRITE_FILLER_SUPPORTED)
/* Add a filler byte on read, or remove a filler or alpha byte on write.
 * The filler type has changed in v0.95 to allow future 2-byte fillers
 * for 48-bit input data, as well as to avoid problems with some compilers
 * that don't like bytes as parameters.
 */
void PNGAPI
png_set_filler(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
{
   png_debug(1, "in png_set_filler");

   if (png_ptr == NULL)
      return;

   /* In libpng 1.6 it is possible to determine whether this is a read or write
    * operation and therefore to do more checking here for a valid call.
    */
   if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0)
   {
#     ifdef PNG_READ_FILLER_SUPPORTED
         /* On read png_set_filler is always valid, regardless of the base PNG
          * format, because other transformations can give a format where the
          * filler code can execute (basically an 8 or 16-bit component RGB or G
          * format.)
          *
          * NOTE: usr_channels is not used by the read code!  (This has led to
          * confusion in the past.)  The filler is only used in the read code.
          */
         png_ptr->filler = PNG_UINT_16(filler); /* Max bit depth is 16 */
#     else
         png_app_error(png_ptr, "png_set_filler not supported on read");
         PNG_UNUSED(filler) /* not used in the write case */
         return;
#     endif
   }

   else /* write */
   {
#     ifdef PNG_WRITE_FILLER_SUPPORTED
         /* On write the usr_channels parameter must be set correctly at the
          * start to record the number of channels in the app-supplied data.
          */
         switch (png_ptr->color_type)
         {
            case PNG_COLOR_TYPE_RGB:
               png_ptr->usr_channels = 4;
               break;

            case PNG_COLOR_TYPE_GRAY:
               if (png_ptr->bit_depth >= 8)
               {
                  png_ptr->usr_channels = 2;
                  break;
               }

               else
               {
                  /* There simply isn't any code in libpng to strip out bits
                   * from bytes when the components are less than a byte in
                   * size!
                   */
                  png_app_error(png_ptr,
                     "png_set_filler is invalid for low bit depth gray output");
                  return;
               }

            default:
               png_app_error(png_ptr,
                  "png_set_filler: inappropriate color type");
               return;
         }
#     else
         png_app_error(png_ptr, "png_set_filler not supported on write");
         return;
#     endif
   }

   /* Here on success - libpng supports the operation, set the transformation
    * and the flag to say where the filler channel is.
    */
   png_ptr->transformations |= PNG_FILLER;

   if (filler_loc == PNG_FILLER_AFTER)
      png_ptr->flags |= PNG_FLAG_FILLER_AFTER;

   else
      png_ptr->flags &= ~PNG_FLAG_FILLER_AFTER;
}

/* Added to libpng-1.2.7 */
void PNGAPI
png_set_add_alpha(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
{
   png_debug(1, "in png_set_add_alpha");

   if (png_ptr == NULL)
      return;

   png_set_filler(png_ptr, filler, filler_loc);
   /* The above may fail to do anything. */
   if ((png_ptr->transformations & PNG_FILLER) != 0)
      png_ptr->transformations |= PNG_ADD_ALPHA;
}

#endif

#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED) || \
    defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
void PNGAPI
png_set_swap_alpha(png_structrp png_ptr)
{
   png_debug(1, "in png_set_swap_alpha");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_SWAP_ALPHA;
}
#endif

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED) || \
    defined(PNG_WRITE_INVERT_ALPHA_SUPPORTED)
void PNGAPI
png_set_invert_alpha(png_structrp png_ptr)
{
   png_debug(1, "in png_set_invert_alpha");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_INVERT_ALPHA;
}
#endif

#if defined(PNG_READ_INVERT_SUPPORTED) || defined(PNG_WRITE_INVERT_SUPPORTED)
void PNGAPI
png_set_invert_mono(png_structrp png_ptr)
{
   png_debug(1, "in png_set_invert_mono");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_INVERT_MONO;
}

/* Invert monochrome grayscale data */
void /* PRIVATE */
png_do_invert(png_transform_controlp row_info, png_bytep row)
{
   png_debug(1, "in png_do_invert");

#  define png_ptr row_info->png_ptr

  /* This test removed from libpng version 1.0.13 and 1.2.0:
   *   if (row_info->bit_depth == 1 &&
   */
   if (row_info->channels == 1)
   {
      if (!(row_info->flags & PNG_INDEXED)) /* GRAY */
      {
         png_bytep rp = row + png_transform_rowbytes(row_info);

         /* Don't care about the bit depth: */
         while (rp > row)
            *--rp ^= 0xff;

         row_info->flags |= PNG_INVERTED;
      }
   }

   else if (row_info->channels == 2) /* GRAY ALPHA */
   {
      if (row_info->bit_depth == 8)
      {
         png_bytep rp;

         row_info->flags |= PNG_INVERTED;
         rp = row + png_transform_rowbytes(row_info);

         /* Go backwards, so rp[-1] is alpha and rp[-2] is gray: */
         while (rp >= row+2)
            rp -= 2, *rp ^= 0xff;
      }

#  ifdef PNG_16BIT_SUPPORTED
      else if (row_info->bit_depth == 16)
      {
         png_bytep rp;

         row_info->flags |= PNG_INVERTED;
         rp = row + png_transform_rowbytes(row_info);

         /* The same, but now we have GGAA: */
         while (rp >= row+4)
            rp -= 3, *rp ^= 0xff, *--rp ^= 0xff;
      }
#  endif
   }
#  undef png_ptr
}
#endif /* READ_INVERT || WRITE_INVERT */

#ifdef PNG_16BIT_SUPPORTED
#if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
/* Swaps byte order on 16 bit depth images */
void /* PRIVATE */
png_do_swap(png_transform_controlp row_info, png_bytep row)
{
   png_debug(1, "in png_do_swap");

#  define png_ptr row_info->png_ptr

   if (row_info->bit_depth == 16)
   {
      png_bytep rp;

      row_info->flags |= PNG_BYTE_SWAPPED;
      rp = row + png_transform_rowbytes(row_info);

      while (rp >= row+2)
      {
         png_byte save = *--rp;
         *rp = rp[-1], --rp;
         *rp = save;
      }
   }
#  undef png_ptr
}
#endif /* READ_SWAP || WRITE_SWAP */
#endif /* 16_BIT */

#if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
static PNG_CONST png_byte onebppswaptable[256] = {
   0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
   0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
   0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
   0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
   0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
   0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
   0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
   0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
   0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
   0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
   0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
   0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
   0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
   0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
   0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
   0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
   0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
   0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
   0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
   0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
   0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
   0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
   0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
   0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
   0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
   0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
   0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
   0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
   0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
   0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
   0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
   0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
};

static PNG_CONST png_byte twobppswaptable[256] = {
   0x00, 0x40, 0x80, 0xC0, 0x10, 0x50, 0x90, 0xD0,
   0x20, 0x60, 0xA0, 0xE0, 0x30, 0x70, 0xB0, 0xF0,
   0x04, 0x44, 0x84, 0xC4, 0x14, 0x54, 0x94, 0xD4,
   0x24, 0x64, 0xA4, 0xE4, 0x34, 0x74, 0xB4, 0xF4,
   0x08, 0x48, 0x88, 0xC8, 0x18, 0x58, 0x98, 0xD8,
   0x28, 0x68, 0xA8, 0xE8, 0x38, 0x78, 0xB8, 0xF8,
   0x0C, 0x4C, 0x8C, 0xCC, 0x1C, 0x5C, 0x9C, 0xDC,
   0x2C, 0x6C, 0xAC, 0xEC, 0x3C, 0x7C, 0xBC, 0xFC,
   0x01, 0x41, 0x81, 0xC1, 0x11, 0x51, 0x91, 0xD1,
   0x21, 0x61, 0xA1, 0xE1, 0x31, 0x71, 0xB1, 0xF1,
   0x05, 0x45, 0x85, 0xC5, 0x15, 0x55, 0x95, 0xD5,
   0x25, 0x65, 0xA5, 0xE5, 0x35, 0x75, 0xB5, 0xF5,
   0x09, 0x49, 0x89, 0xC9, 0x19, 0x59, 0x99, 0xD9,
   0x29, 0x69, 0xA9, 0xE9, 0x39, 0x79, 0xB9, 0xF9,
   0x0D, 0x4D, 0x8D, 0xCD, 0x1D, 0x5D, 0x9D, 0xDD,
   0x2D, 0x6D, 0xAD, 0xED, 0x3D, 0x7D, 0xBD, 0xFD,
   0x02, 0x42, 0x82, 0xC2, 0x12, 0x52, 0x92, 0xD2,
   0x22, 0x62, 0xA2, 0xE2, 0x32, 0x72, 0xB2, 0xF2,
   0x06, 0x46, 0x86, 0xC6, 0x16, 0x56, 0x96, 0xD6,
   0x26, 0x66, 0xA6, 0xE6, 0x36, 0x76, 0xB6, 0xF6,
   0x0A, 0x4A, 0x8A, 0xCA, 0x1A, 0x5A, 0x9A, 0xDA,
   0x2A, 0x6A, 0xAA, 0xEA, 0x3A, 0x7A, 0xBA, 0xFA,
   0x0E, 0x4E, 0x8E, 0xCE, 0x1E, 0x5E, 0x9E, 0xDE,
   0x2E, 0x6E, 0xAE, 0xEE, 0x3E, 0x7E, 0xBE, 0xFE,
   0x03, 0x43, 0x83, 0xC3, 0x13, 0x53, 0x93, 0xD3,
   0x23, 0x63, 0xA3, 0xE3, 0x33, 0x73, 0xB3, 0xF3,
   0x07, 0x47, 0x87, 0xC7, 0x17, 0x57, 0x97, 0xD7,
   0x27, 0x67, 0xA7, 0xE7, 0x37, 0x77, 0xB7, 0xF7,
   0x0B, 0x4B, 0x8B, 0xCB, 0x1B, 0x5B, 0x9B, 0xDB,
   0x2B, 0x6B, 0xAB, 0xEB, 0x3B, 0x7B, 0xBB, 0xFB,
   0x0F, 0x4F, 0x8F, 0xCF, 0x1F, 0x5F, 0x9F, 0xDF,
   0x2F, 0x6F, 0xAF, 0xEF, 0x3F, 0x7F, 0xBF, 0xFF
};

static PNG_CONST png_byte fourbppswaptable[256] = {
   0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70,
   0x80, 0x90, 0xA0, 0xB0, 0xC0, 0xD0, 0xE0, 0xF0,
   0x01, 0x11, 0x21, 0x31, 0x41, 0x51, 0x61, 0x71,
   0x81, 0x91, 0xA1, 0xB1, 0xC1, 0xD1, 0xE1, 0xF1,
   0x02, 0x12, 0x22, 0x32, 0x42, 0x52, 0x62, 0x72,
   0x82, 0x92, 0xA2, 0xB2, 0xC2, 0xD2, 0xE2, 0xF2,
   0x03, 0x13, 0x23, 0x33, 0x43, 0x53, 0x63, 0x73,
   0x83, 0x93, 0xA3, 0xB3, 0xC3, 0xD3, 0xE3, 0xF3,
   0x04, 0x14, 0x24, 0x34, 0x44, 0x54, 0x64, 0x74,
   0x84, 0x94, 0xA4, 0xB4, 0xC4, 0xD4, 0xE4, 0xF4,
   0x05, 0x15, 0x25, 0x35, 0x45, 0x55, 0x65, 0x75,
   0x85, 0x95, 0xA5, 0xB5, 0xC5, 0xD5, 0xE5, 0xF5,
   0x06, 0x16, 0x26, 0x36, 0x46, 0x56, 0x66, 0x76,
   0x86, 0x96, 0xA6, 0xB6, 0xC6, 0xD6, 0xE6, 0xF6,
   0x07, 0x17, 0x27, 0x37, 0x47, 0x57, 0x67, 0x77,
   0x87, 0x97, 0xA7, 0xB7, 0xC7, 0xD7, 0xE7, 0xF7,
   0x08, 0x18, 0x28, 0x38, 0x48, 0x58, 0x68, 0x78,
   0x88, 0x98, 0xA8, 0xB8, 0xC8, 0xD8, 0xE8, 0xF8,
   0x09, 0x19, 0x29, 0x39, 0x49, 0x59, 0x69, 0x79,
   0x89, 0x99, 0xA9, 0xB9, 0xC9, 0xD9, 0xE9, 0xF9,
   0x0A, 0x1A, 0x2A, 0x3A, 0x4A, 0x5A, 0x6A, 0x7A,
   0x8A, 0x9A, 0xAA, 0xBA, 0xCA, 0xDA, 0xEA, 0xFA,
   0x0B, 0x1B, 0x2B, 0x3B, 0x4B, 0x5B, 0x6B, 0x7B,
   0x8B, 0x9B, 0xAB, 0xBB, 0xCB, 0xDB, 0xEB, 0xFB,
   0x0C, 0x1C, 0x2C, 0x3C, 0x4C, 0x5C, 0x6C, 0x7C,
   0x8C, 0x9C, 0xAC, 0xBC, 0xCC, 0xDC, 0xEC, 0xFC,
   0x0D, 0x1D, 0x2D, 0x3D, 0x4D, 0x5D, 0x6D, 0x7D,
   0x8D, 0x9D, 0xAD, 0xBD, 0xCD, 0xDD, 0xED, 0xFD,
   0x0E, 0x1E, 0x2E, 0x3E, 0x4E, 0x5E, 0x6E, 0x7E,
   0x8E, 0x9E, 0xAE, 0xBE, 0xCE, 0xDE, 0xEE, 0xFE,
   0x0F, 0x1F, 0x2F, 0x3F, 0x4F, 0x5F, 0x6F, 0x7F,
   0x8F, 0x9F, 0xAF, 0xBF, 0xCF, 0xDF, 0xEF, 0xFF
};

/* Swaps pixel packing order within bytes */
void /* PRIVATE */
png_do_packswap(png_transform_controlp row_info, png_bytep row)
{
   png_debug(1, "in png_do_packswap");

#  define png_ptr row_info->png_ptr

   if (row_info->bit_depth < 8)
   {
      png_bytep ep;
      png_const_bytep table;

      if (row_info->bit_depth == 1)
         table = onebppswaptable;

      else if (row_info->bit_depth == 2)
         table = twobppswaptable;

      else if (row_info->bit_depth == 4)
         table = fourbppswaptable;

      else
         return;

      row_info->flags |= PNG_PIXEL_SWAPPED;
      ep = row + png_transform_rowbytes(row_info);

      while (row < ep)
         *row = table[*row], ++row;
   }
#  undef png_ptr
}
#endif /* READ_PACKSWAP || WRITE_PACKSWAP */

#if defined(PNG_WRITE_FILLER_SUPPORTED) || \
    defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
/* Remove a channel - this used to be 'png_do_strip_filler' but it used a
 * somewhat weird combination of flags to determine what to do.  All the calls
 * to png_do_strip_filler are changed in 1.5.2 to call this instead with the
 * correct arguments.
 *
 * The routine isn't general - the channel must be the channel at the start or
 * end (not in the middle) of each pixel.
 */
void /* PRIVATE */
png_do_strip_channel(png_transform_controlp row_info, png_bytep row,
   int at_start)
{
   png_const_bytep sp = row; /* source pointer */
   png_bytep       dp = row; /* destination pointer */
   png_const_bytep ep = row + png_transform_rowbytes(row_info); /* beyond end */

#  define png_ptr row_info->png_ptr

   /* At the start sp will point to the first byte to copy and dp to where
    * it is copied to.  ep always points just beyond the end of the row, so
    * the loop simply copies (channels-1) channels until sp reaches ep.
    *
    * at_start:        0 -- convert AG, XG, ARGB, XRGB, AAGG, XXGG, etc.
    *            nonzero -- convert GA, GX, RGBA, RGBX, GGAA, RRGGBBXX, etc.
    */

   /* GA, GX, XG cases */
   if (row_info->channels == 2)
   {
      if (row_info->bit_depth == 8)
      {
         if (at_start != 0) /* Skip initial filler */
            ++sp;
         else          /* Skip initial channel and, for sp, the filler */
            sp += 2, ++dp;

         /* For a 1 pixel wide image there is nothing to do */
         while (sp < ep)
            *dp++ = *sp, sp += 2;
      }

      else if (row_info->bit_depth == 16)
      {
         if (at_start != 0) /* Skip initial filler */
            sp += 2;
         else          /* Skip initial channel and, for sp, the filler */
            sp += 4, dp += 2;

         while (sp < ep)
            *dp++ = *sp++, *dp++ = *sp, sp += 3;
      }

      else
         return; /* bad bit depth */

      row_info->channels = 1;
      debug(dp == row + png_transform_rowbytes(row_info));
   }

   /* RGBA, RGBX, XRGB cases */
   else if (row_info->channels == 4)
   {
      if (row_info->bit_depth == 8)
      {
         if (at_start != 0) /* Skip initial filler */
            ++sp;
         else          /* Skip initial channels and, for sp, the filler */
            sp += 4, dp += 3;

         /* Note that the loop adds 3 to dp and 4 to sp each time. */
         while (sp < ep)
            *dp++ = *sp++, *dp++ = *sp++, *dp++ = *sp, sp += 2;
      }

      else if (row_info->bit_depth == 16)
      {
         if (at_start != 0) /* Skip initial filler */
            sp += 2;
         else          /* Skip initial channels and, for sp, the filler */
            sp += 8, dp += 6;

         while (sp < ep)
         {
            /* Copy 6 bytes, skip 2 */
            *dp++ = *sp++, *dp++ = *sp++;
            *dp++ = *sp++, *dp++ = *sp++;
            *dp++ = *sp++, *dp++ = *sp, sp += 3;
         }
      }

      else
         return; /* bad bit depth */

      row_info->channels = 3;
      debug(dp == row + png_transform_rowbytes(row_info));
   }

   else
      return; /* The filler channel has gone already */
#  undef png_ptr
}
#endif /* WRITE_FILLER || READ_STRIP_ALPHA */

#if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
/* Swaps red and blue bytes within a pixel */
void /* PRIVATE */
png_do_bgr(png_transform_controlp row_info, png_bytep row)
{
   unsigned int channels;

   png_debug(1, "in png_do_bgr");

#  define png_ptr row_info->png_ptr

   channels = row_info->channels;

   if (channels == 3 || channels == 4)
   {
      png_const_bytep ep = row + png_transform_rowbytes(row_info);

      if (row_info->bit_depth == 8)
      {
         ep -= channels; /* Last pixel */
         row_info->flags ^= PNG_RGB_SWAPPED;

         while (row <= ep)
         {
            png_byte save = row[0];
            row[0] = row[2];
            row[2] = save;
            row += channels;
         }

         debug(row == ep+channels);
      }

#     ifdef PNG_16BIT_SUPPORTED
         else if (row_info->bit_depth == 16)
         {
            channels *= 2; /* now in bytes */

            ep -= channels; /* Last pixel */
            row_info->flags |= PNG_RGB_SWAPPED;

            while (row <= ep)
            {
               png_byte save = row[0];
               row[0] = row[4];
               row[4] = save;

               save = row[1];
               row[1] = row[5];
               row[5] = save;

               row += channels;
            }

            debug(row == ep+channels);
         }
#     endif
   }
#  undef png_ptr
}
#endif /* READ_BGR || WRITE_BGR */

#if defined(PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED) || \
    defined(PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED)
/* Added at libpng-1.5.10 */
void /* PRIVATE */
png_do_check_palette_indexes(png_structrp png_ptr,
   png_transform_controlp row_info)
{
   if (png_ptr->num_palette < (1 << row_info->bit_depth) &&
      png_ptr->num_palette > 0) /* num_palette can be 0 in MNG files */
   {
      /* Padding is the unused bits in the last byte: 8 - bits-in-last-byte,
       * which reduces to 7 & (-total_bits), so we don't care about overflow
       * in the unsigned calculation here:
       */
      unsigned int padding =
         7 & -(row_info->bit_depth * row_info->channels * row_info->width);
      png_bytep rp = png_ptr->row_buf + png_transform_rowbytes(row_info);

      /* Note that png_ptr->row_buf starts with a filter byte, so rp is
       * currently pointing to the last byte in the row, not just after
       * it.
       */

      switch (row_info->bit_depth)
      {
         case 1:
         {
            /* in this case, all bytes must be 0 so we don't need
             * to unpack the pixels except for the rightmost one.
             */
            for (; rp > png_ptr->row_buf; rp--)
            {
              if ((*rp >> padding) != 0)
                 png_ptr->num_palette_max = 1;
              padding = 0;
            }

            break;
         }

         case 2:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
              int i = ((*rp >> padding) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 2) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 4) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 6) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              padding = 0;
            }

            break;
         }

         case 4:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
              int i = ((*rp >> padding) & 0x0f);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 4) & 0x0f);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              padding = 0;
            }

            break;
         }

         case 8:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
               if (*rp > png_ptr->num_palette_max)
                  png_ptr->num_palette_max = (int) *rp;
            }

            break;
         }

         default:
            break;
      }
   }
}
#endif /* CHECK_FOR_INVALID_INDEX */

#if defined(PNG_READ_TRANSFORMS_SUPPORTED) ||\
    defined(PNG_WRITE_TRANSFORMS_SUPPORTED)
/* Utility functions: */
void
png_init_transform_control(png_const_structrp png_ptr,
   png_transform_controlp out, png_const_row_infop row_info)
{
   out->png_ptr = png_ptr;

   /* At the start expect row_info to be consistent with png_ptr: */
   if (png_ptr->mode & PNG_IS_READ_STRUCT)
   {
      debug(png_ptr->iwidth == row_info->width);
      debug(png_ptr->color_type == row_info->color_type);
      debug(png_ptr->bit_depth == row_info->bit_depth);
   }

   out->width = row_info->width;
   out->flags = 0;
   out->bit_depth = row_info->bit_depth;

   switch (row_info->color_type)
   {
      case PNG_COLOR_TYPE_GRAY:
         out->channels = 1;
         break;

      case PNG_COLOR_TYPE_GRAY_ALPHA:
         out->channels = 2;
         break;

      case PNG_COLOR_TYPE_PALETTE:
         affirm(!(png_ptr->mode & PNG_IS_READ_STRUCT) ||
            png_ptr->palette != NULL);
         out->flags |= PNG_INDEXED;
         out->channels = 1;
         break;

      case PNG_COLOR_TYPE_RGB:
         out->channels = 3;
         break;

      case PNG_COLOR_TYPE_RGB_ALPHA:
         out->channels = 4;
         break;

      default:
         impossible("invalid PNG color type");
   } 
}

size_t
png_transform_rowbytes(png_const_transform_controlp row_info)
{
#  define png_ptr row_info->png_ptr
   /* For this not to overflow the pixel depth calculation must not overflow
    * and the pixel depth must be less than maximum_pixel_depth.
    */
   /* The release code uses PNG_ROWBYTES, so make sure that it will not
    * overflow.  To test this it is necessary to generate some very wide
    * images and ensure that the code errors out before getting here.
    */
   unsigned int channels = row_info->channels;
   unsigned int bit_depth = row_info->bit_depth;
   unsigned int pixel_bits = channels * bit_depth;
   size_t width = row_info->width;

   affirm(bit_depth < 256 && channels < 256 &&
      pixel_bits <= png_ptr->maximum_pixel_depth);

   return PNG_ROWBYTES(pixel_bits, width);
#  undef png_ptr
}

static unsigned int
transform_color_type(png_const_transform_controlp row_info)
{
   const unsigned int ch = row_info->channels - 1;
   const unsigned int indexed = row_info->flags & PNG_INDEXED;

   /* That is 0, 1, 2, 3 for G/PALETTE, GA, RGB, RGBA.  Check the
    * numbers:
    */
#  if PNG_INDEXED != PNG_COLOR_MASK_PALETTE ||\
      PNG_FILLER_IN_ALPHA != PNG_COLOR_MASK_ALPHA ||\
      PNG_COLOR_MASK_PALETTE != 1 ||\
      PNG_COLOR_MASK_COLOR != 2 ||\
      PNG_COLOR_MASK_ALPHA != 4
#     error Unexpected PNG color type defines
#  endif

   /* The following preserves all the bits in row_info->channels except the
    * top bit and generates a correct PNG color type for the defined values
    * and an incorrect one for all undefined cases.
    *
    * Note that when PNG_FILLER_IN_ALPHA is set in the flags
    */
   return indexed /*PALETTE*/ |
          ((ch & 2) ^ (indexed << 1) /*COLOR*/) |
          (((ch & 1) << 2/*ALPHA*/) & ~row_info->flags) |
          ((ch & ~3) << 1 /*INVALID*/);
}

void
png_end_transform_control(png_row_infop out, png_const_transform_controlp in)
{
#  define png_ptr in->png_ptr /* for affirm/impossible */
   out->width = in->width;
   out->rowbytes = png_transform_rowbytes(in);

   out->color_type = png_check_byte(png_ptr, transform_color_type(in));
   out->bit_depth = png_check_byte(png_ptr, in->bit_depth);
   out->channels = png_check_byte(png_ptr, in->channels);
   out->pixel_depth = png_check_byte(png_ptr, in->channels * in->bit_depth);

#  ifdef PNG_WARNINGS_SUPPORTED
      if ((in->flags & PNG_BAD_INDEX) != 0)
         png_warning(png_ptr, "palette image had bad index");
#  endif

   /* At the end expect row_info to be consistent with png_ptr: */
   if (!(png_ptr->mode & PNG_IS_READ_STRUCT))
   {
      debug(png_ptr->color_type == out->color_type);
      debug(png_ptr->bit_depth == out->bit_depth);
   }
#  undef png_ptr
}
#endif /* READ_TRANSFORMS | WRITE_TRANSFORMS */

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
void PNGAPI
png_set_user_transform_info(png_structrp png_ptr, png_voidp
   user_transform_ptr, int user_transform_depth, int user_transform_channels)
{
   png_debug(1, "in png_set_user_transform_info");

   if (png_ptr == NULL)
      return;

#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
   if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
      (png_ptr->flags & PNG_FLAG_ROW_INIT) != 0)
   {
      png_app_error(png_ptr,
            "info change after png_start_read_image or png_read_update_info");
      return;
   }
#endif

   png_ptr->user_transform_ptr = user_transform_ptr;
   png_ptr->user_transform_depth = png_check_byte(png_ptr,
      user_transform_depth);
   png_ptr->user_transform_channels = png_check_byte(png_ptr,
      user_transform_channels);
}
#endif

/* This function returns a pointer to the user_transform_ptr associated with
 * the user transform functions.  The application should free any memory
 * associated with this pointer before png_write_destroy and png_read_destroy
 * are called.
 */
#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
png_voidp PNGAPI
png_get_user_transform_ptr(png_const_structrp png_ptr)
{
   if (png_ptr == NULL)
      return (NULL);

   return png_ptr->user_transform_ptr;
}
#endif

#ifdef PNG_USER_TRANSFORM_INFO_SUPPORTED
png_uint_32 PNGAPI
png_get_current_row_number(png_const_structrp png_ptr)
{
   /* See the comments in png.h - this is the sub-image row when reading an
    * interlaced image.
    */
   if (png_ptr != NULL)
      return png_ptr->row_number;

   return PNG_UINT_32_MAX; /* help the app not to fail silently */
}

png_byte PNGAPI
png_get_current_pass_number(png_const_structrp png_ptr)
{
   if (png_ptr != NULL)
      return png_ptr->pass;
   return 8; /* invalid */
}
#endif /* USER_TRANSFORM_INFO */
#endif /* READ_USER_TRANSFORM || WRITE_USER_TRANSFORM */
#endif /* READ || WRITE */