/lib_png/base/libpng-1.6.16/contrib/libtests/pngvalid.c

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/* pngvalid.c - validate libpng by constructing then reading png files.
 *
 * Last changed in libpng 1.6.14 [October 23, 2014]
 * Copyright (c) 2014 Glenn Randers-Pehrson
 * Written by John Cunningham Bowler
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * NOTES:
 *   This is a C program that is intended to be linked against libpng.  It
 *   generates bitmaps internally, stores them as PNG files (using the
 *   sequential write code) then reads them back (using the sequential
 *   read code) and validates that the result has the correct data.
 *
 *   The program can be modified and extended to test the correctness of
 *   transformations performed by libpng.
 */

#define _POSIX_SOURCE 1
#define _ISOC99_SOURCE 1 /* For floating point */
#define _GNU_SOURCE 1 /* For the floating point exception extension */

#include <signal.h>
#include <stdio.h>

#if defined(HAVE_CONFIG_H) && !defined(PNG_NO_CONFIG_H)
#  include <config.h>
#endif

#ifdef HAVE_FEENABLEEXCEPT /* from config.h, if included */
#  include <fenv.h>
#endif

#ifndef FE_DIVBYZERO
#  define FE_DIVBYZERO 0
#endif
#ifndef FE_INVALID
#  define FE_INVALID 0
#endif
#ifndef FE_OVERFLOW
#  define FE_OVERFLOW 0
#endif

/* Define the following to use this test against your installed libpng, rather
 * than the one being built here:
 */
#ifdef PNG_FREESTANDING_TESTS
#  include <png.h>
#else
#  include "../../png.h"
#endif

#ifdef PNG_ZLIB_HEADER
#  include PNG_ZLIB_HEADER
#else
#  include <zlib.h>   /* For crc32 */
#endif

/* 1.6.1 added support for the configure test harness, which uses 77 to indicate
 * a skipped test, in earlier versions we need to succeed on a skipped test, so:
 */
#if PNG_LIBPNG_VER < 10601
#  define SKIP 0
#else
#  define SKIP 77
#endif

/* pngvalid requires write support and one of the fixed or floating point APIs.
 */
#if defined(PNG_WRITE_SUPPORTED) &&\
   (defined(PNG_FIXED_POINT_SUPPORTED) || defined(PNG_FLOATING_POINT_SUPPORTED))

#if PNG_LIBPNG_VER < 10500
/* This deliberately lacks the PNG_CONST. */
typedef png_byte *png_const_bytep;

/* This is copied from 1.5.1 png.h: */
#define PNG_INTERLACE_ADAM7_PASSES 7
#define PNG_PASS_START_ROW(pass) (((1U&~(pass))<<(3-((pass)>>1)))&7)
#define PNG_PASS_START_COL(pass) (((1U& (pass))<<(3-(((pass)+1)>>1)))&7)
#define PNG_PASS_ROW_SHIFT(pass) ((pass)>2?(8-(pass))>>1:3)
#define PNG_PASS_COL_SHIFT(pass) ((pass)>1?(7-(pass))>>1:3)
#define PNG_PASS_ROWS(height, pass) (((height)+(((1<<PNG_PASS_ROW_SHIFT(pass))\
   -1)-PNG_PASS_START_ROW(pass)))>>PNG_PASS_ROW_SHIFT(pass))
#define PNG_PASS_COLS(width, pass) (((width)+(((1<<PNG_PASS_COL_SHIFT(pass))\
   -1)-PNG_PASS_START_COL(pass)))>>PNG_PASS_COL_SHIFT(pass))
#define PNG_ROW_FROM_PASS_ROW(yIn, pass) \
   (((yIn)<<PNG_PASS_ROW_SHIFT(pass))+PNG_PASS_START_ROW(pass))
#define PNG_COL_FROM_PASS_COL(xIn, pass) \
   (((xIn)<<PNG_PASS_COL_SHIFT(pass))+PNG_PASS_START_COL(pass))
#define PNG_PASS_MASK(pass,off) ( \
   ((0x110145AFU>>(((7-(off))-(pass))<<2)) & 0xFU) | \
   ((0x01145AF0U>>(((7-(off))-(pass))<<2)) & 0xF0U))
#define PNG_ROW_IN_INTERLACE_PASS(y, pass) \
   ((PNG_PASS_MASK(pass,0) >> ((y)&7)) & 1)
#define PNG_COL_IN_INTERLACE_PASS(x, pass) \
   ((PNG_PASS_MASK(pass,1) >> ((x)&7)) & 1)

/* These are needed too for the default build: */
#define PNG_WRITE_16BIT_SUPPORTED
#define PNG_READ_16BIT_SUPPORTED

/* This comes from pnglibconf.h afer 1.5: */
#define PNG_FP_1 100000
#define PNG_GAMMA_THRESHOLD_FIXED\
   ((png_fixed_point)(PNG_GAMMA_THRESHOLD * PNG_FP_1))
#endif

#if PNG_LIBPNG_VER < 10600
   /* 1.6.0 constifies many APIs, the following exists to allow pngvalid to be
    * compiled against earlier versions.
    */
#  define png_const_structp png_structp
#endif

#include <float.h>  /* For floating point constants */
#include <stdlib.h> /* For malloc */
#include <string.h> /* For memcpy, memset */
#include <math.h>   /* For floor */

/* Unused formal parameter errors are removed using the following macro which is
 * expected to have no bad effects on performance.
 */
#ifndef UNUSED
#  if defined(__GNUC__) || defined(_MSC_VER)
#     define UNUSED(param) (void)param;
#  else
#     define UNUSED(param)
#  endif
#endif

/***************************** EXCEPTION HANDLING *****************************/
#ifdef PNG_FREESTANDING_TESTS
#  include <cexcept.h>
#else
#  include "../visupng/cexcept.h"
#endif

#ifdef __cplusplus
#  define this not_the_cpp_this
#  define new not_the_cpp_new
#  define voidcast(type, value) static_cast<type>(value)
#else
#  define voidcast(type, value) (value)
#endif /* __cplusplus */

struct png_store;
define_exception_type(struct png_store*);

/* The following are macros to reduce typing everywhere where the well known
 * name 'the_exception_context' must be defined.
 */
#define anon_context(ps) struct exception_context *the_exception_context = \
   &(ps)->exception_context
#define context(ps,fault) anon_context(ps); png_store *fault

/* This macro returns the number of elements in an array as an (unsigned int),
 * it is necessary to avoid the inability of certain versions of GCC to use
 * the value of a compile-time constant when performing range checks.  It must
 * be passed an array name.
 */
#define ARRAY_SIZE(a) ((unsigned int)((sizeof (a))/(sizeof (a)[0])))

/******************************* UTILITIES ************************************/
/* Error handling is particularly problematic in production code - error
 * handlers often themselves have bugs which lead to programs that detect
 * minor errors crashing.  The following functions deal with one very
 * common class of errors in error handlers - attempting to format error or
 * warning messages into buffers that are too small.
 */
static size_t safecat(char *buffer, size_t bufsize, size_t pos,
   PNG_CONST char *cat)
{
   while (pos < bufsize && cat != NULL && *cat != 0)
      buffer[pos++] = *cat++;

   if (pos >= bufsize)
      pos = bufsize-1;

   buffer[pos] = 0;
   return pos;
}

static size_t safecatn(char *buffer, size_t bufsize, size_t pos, int n)
{
   char number[64];
   sprintf(number, "%d", n);
   return safecat(buffer, bufsize, pos, number);
}

#ifdef PNG_READ_TRANSFORMS_SUPPORTED
static size_t safecatd(char *buffer, size_t bufsize, size_t pos, double d,
    int precision)
{
   char number[64];
   sprintf(number, "%.*f", precision, d);
   return safecat(buffer, bufsize, pos, number);
}
#endif

static PNG_CONST char invalid[] = "invalid";
static PNG_CONST char sep[] = ": ";

static PNG_CONST char *colour_types[8] =
{
   "grayscale", invalid, "truecolour", "indexed-colour",
   "grayscale with alpha", invalid, "truecolour with alpha", invalid
};

#ifdef PNG_READ_SUPPORTED
/* Convert a double precision value to fixed point. */
static png_fixed_point
fix(double d)
{
   d = floor(d * PNG_FP_1 + .5);
   return (png_fixed_point)d;
}
#endif /* PNG_READ_SUPPORTED */

/* Generate random bytes.  This uses a boring repeatable algorithm and it
 * is implemented here so that it gives the same set of numbers on every
 * architecture.  It's a linear congruential generator (Knuth or Sedgewick
 * "Algorithms") but it comes from the 'feedback taps' table in Horowitz and
 * Hill, "The Art of Electronics" (Pseudo-Random Bit Sequences and Noise
 * Generation.)
 */
static void
make_random_bytes(png_uint_32* seed, void* pv, size_t size)
{
   png_uint_32 u0 = seed[0], u1 = seed[1];
   png_bytep bytes = voidcast(png_bytep, pv);

   /* There are thirty three bits, the next bit in the sequence is bit-33 XOR
    * bit-20.  The top 1 bit is in u1, the bottom 32 are in u0.
    */
   size_t i;
   for (i=0; i<size; ++i)
   {
      /* First generate 8 new bits then shift them in at the end. */
      png_uint_32 u = ((u0 >> (20-8)) ^ ((u1 << 7) | (u0 >> (32-7)))) & 0xff;
      u1 <<= 8;
      u1 |= u0 >> 24;
      u0 <<= 8;
      u0 |= u;
      *bytes++ = (png_byte)u;
   }

   seed[0] = u0;
   seed[1] = u1;
}

static void
make_four_random_bytes(png_uint_32* seed, png_bytep bytes)
{
   make_random_bytes(seed, bytes, 4);
}

#ifdef PNG_READ_SUPPORTED
static void
randomize(void *pv, size_t size)
{
   static png_uint_32 random_seed[2] = {0x56789abc, 0xd};
   make_random_bytes(random_seed, pv, size);
}

#define RANDOMIZE(this) randomize(&(this), sizeof (this))

static unsigned int
random_mod(unsigned int max)
{
   unsigned int x;

   RANDOMIZE(x);

   return x % max; /* 0 .. max-1 */
}

#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
static int
random_choice(void)
{
   unsigned char x;

   RANDOMIZE(x);

   return x & 1;
}
#endif
#endif /* PNG_READ_SUPPORTED */

/* A numeric ID based on PNG file characteristics.  The 'do_interlace' field
 * simply records whether pngvalid did the interlace itself or whether it
 * was done by libpng.  Width and height must be less than 256.  'palette' is an
 * index of the palette to use for formats with a palette (0 otherwise.)
 */
#define FILEID(col, depth, palette, interlace, width, height, do_interlace) \
   ((png_uint_32)((col) + ((depth)<<3) + ((palette)<<8) + ((interlace)<<13) + \
    (((do_interlace)!=0)<<15) + ((width)<<16) + ((height)<<24)))

#define COL_FROM_ID(id) ((png_byte)((id)& 0x7U))
#define DEPTH_FROM_ID(id) ((png_byte)(((id) >> 3) & 0x1fU))
#define PALETTE_FROM_ID(id) (((id) >> 8) & 0x1f)
#define INTERLACE_FROM_ID(id) ((int)(((id) >> 13) & 0x3))
#define DO_INTERLACE_FROM_ID(id) ((int)(((id)>>15) & 1))
#define WIDTH_FROM_ID(id) (((id)>>16) & 0xff)
#define HEIGHT_FROM_ID(id) (((id)>>24) & 0xff)

/* Utility to construct a standard name for a standard image. */
static size_t
standard_name(char *buffer, size_t bufsize, size_t pos, png_byte colour_type,
    int bit_depth, unsigned int npalette, int interlace_type,
    png_uint_32 w, png_uint_32 h, int do_interlace)
{
   pos = safecat(buffer, bufsize, pos, colour_types[colour_type]);
   if (npalette > 0)
   {
      pos = safecat(buffer, bufsize, pos, "[");
      pos = safecatn(buffer, bufsize, pos, npalette);
      pos = safecat(buffer, bufsize, pos, "]");
   }
   pos = safecat(buffer, bufsize, pos, " ");
   pos = safecatn(buffer, bufsize, pos, bit_depth);
   pos = safecat(buffer, bufsize, pos, " bit");

   if (interlace_type != PNG_INTERLACE_NONE)
   {
      pos = safecat(buffer, bufsize, pos, " interlaced");
      if (do_interlace)
         pos = safecat(buffer, bufsize, pos, "(pngvalid)");
      else
         pos = safecat(buffer, bufsize, pos, "(libpng)");
   }

   if (w > 0 || h > 0)
   {
      pos = safecat(buffer, bufsize, pos, " ");
      pos = safecatn(buffer, bufsize, pos, w);
      pos = safecat(buffer, bufsize, pos, "x");
      pos = safecatn(buffer, bufsize, pos, h);
   }

   return pos;
}

static size_t
standard_name_from_id(char *buffer, size_t bufsize, size_t pos, png_uint_32 id)
{
   return standard_name(buffer, bufsize, pos, COL_FROM_ID(id),
      DEPTH_FROM_ID(id), PALETTE_FROM_ID(id), INTERLACE_FROM_ID(id),
      WIDTH_FROM_ID(id), HEIGHT_FROM_ID(id), DO_INTERLACE_FROM_ID(id));
}

/* Convenience API and defines to list valid formats.  Note that 16 bit read and
 * write support is required to do 16 bit read tests (we must be able to make a
 * 16 bit image to test!)
 */
#ifdef PNG_WRITE_16BIT_SUPPORTED
#  define WRITE_BDHI 4
#  ifdef PNG_READ_16BIT_SUPPORTED
#     define READ_BDHI 4
#     define DO_16BIT
#  endif
#else
#  define WRITE_BDHI 3
#endif
#ifndef DO_16BIT
#  define READ_BDHI 3
#endif

/* The following defines the number of different palettes to generate for
 * each log bit depth of a colour type 3 standard image.
 */
#define PALETTE_COUNT(bit_depth) ((bit_depth) > 4 ? 1U : 16U)

static int
next_format(png_bytep colour_type, png_bytep bit_depth,
   unsigned int* palette_number, int no_low_depth_gray)
{
   if (*bit_depth == 0)
   {
      *colour_type = 0;
      if (no_low_depth_gray)
         *bit_depth = 8;
      else
         *bit_depth = 1;
      *palette_number = 0;
      return 1;
   }

   if (*colour_type == 3)
   {
      /* Add multiple palettes for colour type 3. */
      if (++*palette_number < PALETTE_COUNT(*bit_depth))
         return 1;

      *palette_number = 0;
   }

   *bit_depth = (png_byte)(*bit_depth << 1);

   /* Palette images are restricted to 8 bit depth */
   if (*bit_depth <= 8
#ifdef DO_16BIT
         || (*colour_type != 3 && *bit_depth <= 16)
#endif
      )
      return 1;

   /* Move to the next color type, or return 0 at the end. */
   switch (*colour_type)
   {
      case 0:
         *colour_type = 2;
         *bit_depth = 8;
         return 1;

      case 2:
         *colour_type = 3;
         *bit_depth = 1;
         return 1;

      case 3:
         *colour_type = 4;
         *bit_depth = 8;
         return 1;

      case 4:
         *colour_type = 6;
         *bit_depth = 8;
         return 1;

      default:
         return 0;
   }
}

#ifdef PNG_READ_TRANSFORMS_SUPPORTED
static unsigned int
sample(png_const_bytep row, png_byte colour_type, png_byte bit_depth,
    png_uint_32 x, unsigned int sample_index)
{
   png_uint_32 bit_index, result;

   /* Find a sample index for the desired sample: */
   x *= bit_depth;
   bit_index = x;

   if ((colour_type & 1) == 0) /* !palette */
   {
      if (colour_type & 2)
         bit_index *= 3;

      if (colour_type & 4)
         bit_index += x; /* Alpha channel */

      /* Multiple channels; select one: */
      if (colour_type & (2+4))
         bit_index += sample_index * bit_depth;
   }

   /* Return the sample from the row as an integer. */
   row += bit_index >> 3;
   result = *row;

   if (bit_depth == 8)
      return result;

   else if (bit_depth > 8)
      return (result << 8) + *++row;

   /* Less than 8 bits per sample. */
   bit_index &= 7;
   return (result >> (8-bit_index-bit_depth)) & ((1U<<bit_depth)-1);
}
#endif /* PNG_READ_TRANSFORMS_SUPPORTED */

/* Copy a single pixel, of a given size, from one buffer to another -
 * while this is basically bit addressed there is an implicit assumption
 * that pixels 8 or more bits in size are byte aligned and that pixels
 * do not otherwise cross byte boundaries.  (This is, so far as I know,
 * universally true in bitmap computer graphics.  [JCB 20101212])
 *
 * NOTE: The to and from buffers may be the same.
 */
static void
pixel_copy(png_bytep toBuffer, png_uint_32 toIndex,
   png_const_bytep fromBuffer, png_uint_32 fromIndex, unsigned int pixelSize)
{
   /* Assume we can multiply by 'size' without overflow because we are
    * just working in a single buffer.
    */
   toIndex *= pixelSize;
   fromIndex *= pixelSize;
   if (pixelSize < 8) /* Sub-byte */
   {
      /* Mask to select the location of the copied pixel: */
      unsigned int destMask = ((1U<<pixelSize)-1) << (8-pixelSize-(toIndex&7));
      /* The following read the entire pixels and clears the extra: */
      unsigned int destByte = toBuffer[toIndex >> 3] & ~destMask;
      unsigned int sourceByte = fromBuffer[fromIndex >> 3];

      /* Don't rely on << or >> supporting '0' here, just in case: */
      fromIndex &= 7;
      if (fromIndex > 0) sourceByte <<= fromIndex;
      if ((toIndex & 7) > 0) sourceByte >>= toIndex & 7;

      toBuffer[toIndex >> 3] = (png_byte)(destByte | (sourceByte & destMask));
   }
   else /* One or more bytes */
      memmove(toBuffer+(toIndex>>3), fromBuffer+(fromIndex>>3), pixelSize>>3);
}

#ifdef PNG_READ_SUPPORTED
/* Copy a complete row of pixels, taking into account potential partial
 * bytes at the end.
 */
static void
row_copy(png_bytep toBuffer, png_const_bytep fromBuffer, unsigned int bitWidth)
{
   memcpy(toBuffer, fromBuffer, bitWidth >> 3);

   if ((bitWidth & 7) != 0)
   {
      unsigned int mask;

      toBuffer += bitWidth >> 3;
      fromBuffer += bitWidth >> 3;
      /* The remaining bits are in the top of the byte, the mask is the bits to
       * retain.
       */
      mask = 0xff >> (bitWidth & 7);
      *toBuffer = (png_byte)((*toBuffer & mask) | (*fromBuffer & ~mask));
   }
}

/* Compare pixels - they are assumed to start at the first byte in the
 * given buffers.
 */
static int
pixel_cmp(png_const_bytep pa, png_const_bytep pb, png_uint_32 bit_width)
{
#if PNG_LIBPNG_VER < 10506
   if (memcmp(pa, pb, bit_width>>3) == 0)
   {
      png_uint_32 p;

      if ((bit_width & 7) == 0) return 0;

      /* Ok, any differences? */
      p = pa[bit_width >> 3];
      p ^= pb[bit_width >> 3];

      if (p == 0) return 0;

      /* There are, but they may not be significant, remove the bits
       * after the end (the low order bits in PNG.)
       */
      bit_width &= 7;
      p >>= 8-bit_width;

      if (p == 0) return 0;
   }
#else
   /* From libpng-1.5.6 the overwrite should be fixed, so compare the trailing
    * bits too:
    */
   if (memcmp(pa, pb, (bit_width+7)>>3) == 0)
      return 0;
#endif

   /* Return the index of the changed byte. */
   {
      png_uint_32 where = 0;

      while (pa[where] == pb[where]) ++where;
      return 1+where;
   }
}
#endif /* PNG_READ_SUPPORTED */

/*************************** BASIC PNG FILE WRITING ***************************/
/* A png_store takes data from the sequential writer or provides data
 * to the sequential reader.  It can also store the result of a PNG
 * write for later retrieval.
 */
#define STORE_BUFFER_SIZE 500 /* arbitrary */
typedef struct png_store_buffer
{
   struct png_store_buffer*  prev;    /* NOTE: stored in reverse order */
   png_byte                  buffer[STORE_BUFFER_SIZE];
} png_store_buffer;

#define FILE_NAME_SIZE 64

typedef struct store_palette_entry /* record of a single palette entry */
{
   png_byte red;
   png_byte green;
   png_byte blue;
   png_byte alpha;
} store_palette_entry, store_palette[256];

typedef struct png_store_file
{
   struct png_store_file*  next;      /* as many as you like... */
   char                    name[FILE_NAME_SIZE];
   png_uint_32             id;        /* must be correct (see FILEID) */
   png_size_t              datacount; /* In this (the last) buffer */
   png_store_buffer        data;      /* Last buffer in file */
   int                     npalette;  /* Number of entries in palette */
   store_palette_entry*    palette;   /* May be NULL */
} png_store_file;

/* The following is a pool of memory allocated by a single libpng read or write
 * operation.
 */
typedef struct store_pool
{
   struct png_store    *store;   /* Back pointer */
   struct store_memory *list;    /* List of allocated memory */
   png_byte             mark[4]; /* Before and after data */

   /* Statistics for this run. */
   png_alloc_size_t     max;     /* Maximum single allocation */
   png_alloc_size_t     current; /* Current allocation */
   png_alloc_size_t     limit;   /* Highest current allocation */
   png_alloc_size_t     total;   /* Total allocation */

   /* Overall statistics (retained across successive runs). */
   png_alloc_size_t     max_max;
   png_alloc_size_t     max_limit;
   png_alloc_size_t     max_total;
} store_pool;

typedef struct png_store
{
   /* For cexcept.h exception handling - simply store one of these;
    * the context is a self pointer but it may point to a different
    * png_store (in fact it never does in this program.)
    */
   struct exception_context
                      exception_context;

   unsigned int       verbose :1;
   unsigned int       treat_warnings_as_errors :1;
   unsigned int       expect_error :1;
   unsigned int       expect_warning :1;
   unsigned int       saw_warning :1;
   unsigned int       speed :1;
   unsigned int       progressive :1; /* use progressive read */
   unsigned int       validated :1;   /* used as a temporary flag */
   int                nerrors;
   int                nwarnings;
   int                noptions;       /* number of options below: */
   struct {
      unsigned char   option;         /* option number, 0..30 */
      unsigned char   setting;        /* setting (unset,invalid,on,off) */
   }                  options[16];
   char               test[128];      /* Name of test */
   char               error[256];

   /* Read fields */
   png_structp        pread;    /* Used to read a saved file */
   png_infop          piread;
   png_store_file*    current;  /* Set when reading */
   png_store_buffer*  next;     /* Set when reading */
   png_size_t         readpos;  /* Position in *next */
   png_byte*          image;    /* Buffer for reading interlaced images */
   png_size_t         cb_image; /* Size of this buffer */
   png_size_t         cb_row;   /* Row size of the image(s) */
   png_uint_32        image_h;  /* Number of rows in a single image */
   store_pool         read_memory_pool;

   /* Write fields */
   png_store_file*    saved;
   png_structp        pwrite;   /* Used when writing a new file */
   png_infop          piwrite;
   png_size_t         writepos; /* Position in .new */
   char               wname[FILE_NAME_SIZE];
   png_store_buffer   new;      /* The end of the new PNG file being written. */
   store_pool         write_memory_pool;
   store_palette_entry* palette;
   int                  npalette;
} png_store;

/* Initialization and cleanup */
static void
store_pool_mark(png_bytep mark)
{
   static png_uint_32 store_seed[2] = { 0x12345678, 1};

   make_four_random_bytes(store_seed, mark);
}

#ifdef PNG_READ_SUPPORTED
/* Use this for random 32 bit values; this function makes sure the result is
 * non-zero.
 */
static png_uint_32
random_32(void)
{

   for (;;)
   {
      png_byte mark[4];
      png_uint_32 result;

      store_pool_mark(mark);
      result = png_get_uint_32(mark);

      if (result != 0)
         return result;
   }
}
#endif /* PNG_READ_SUPPORTED */

static void
store_pool_init(png_store *ps, store_pool *pool)
{
   memset(pool, 0, sizeof *pool);

   pool->store = ps;
   pool->list = NULL;
   pool->max = pool->current = pool->limit = pool->total = 0;
   pool->max_max = pool->max_limit = pool->max_total = 0;
   store_pool_mark(pool->mark);
}

static void
store_init(png_store* ps)
{
   memset(ps, 0, sizeof *ps);
   init_exception_context(&ps->exception_context);
   store_pool_init(ps, &ps->read_memory_pool);
   store_pool_init(ps, &ps->write_memory_pool);
   ps->verbose = 0;
   ps->treat_warnings_as_errors = 0;
   ps->expect_error = 0;
   ps->expect_warning = 0;
   ps->saw_warning = 0;
   ps->speed = 0;
   ps->progressive = 0;
   ps->validated = 0;
   ps->nerrors = ps->nwarnings = 0;
   ps->pread = NULL;
   ps->piread = NULL;
   ps->saved = ps->current = NULL;
   ps->next = NULL;
   ps->readpos = 0;
   ps->image = NULL;
   ps->cb_image = 0;
   ps->cb_row = 0;
   ps->image_h = 0;
   ps->pwrite = NULL;
   ps->piwrite = NULL;
   ps->writepos = 0;
   ps->new.prev = NULL;
   ps->palette = NULL;
   ps->npalette = 0;
   ps->noptions = 0;
}

static void
store_freebuffer(png_store_buffer* psb)
{
   if (psb->prev)
   {
      store_freebuffer(psb->prev);
      free(psb->prev);
      psb->prev = NULL;
   }
}

static void
store_freenew(png_store *ps)
{
   store_freebuffer(&ps->new);
   ps->writepos = 0;
   if (ps->palette != NULL)
   {
      free(ps->palette);
      ps->palette = NULL;
      ps->npalette = 0;
   }
}

static void
store_storenew(png_store *ps)
{
   png_store_buffer *pb;

   if (ps->writepos != STORE_BUFFER_SIZE)
      png_error(ps->pwrite, "invalid store call");

   pb = voidcast(png_store_buffer*, malloc(sizeof *pb));

   if (pb == NULL)
      png_error(ps->pwrite, "store new: OOM");

   *pb = ps->new;
   ps->new.prev = pb;
   ps->writepos = 0;
}

static void
store_freefile(png_store_file **ppf)
{
   if (*ppf != NULL)
   {
      store_freefile(&(*ppf)->next);

      store_freebuffer(&(*ppf)->data);
      (*ppf)->datacount = 0;
      if ((*ppf)->palette != NULL)
      {
         free((*ppf)->palette);
         (*ppf)->palette = NULL;
         (*ppf)->npalette = 0;
      }
      free(*ppf);
      *ppf = NULL;
   }
}

/* Main interface to file storeage, after writing a new PNG file (see the API
 * below) call store_storefile to store the result with the given name and id.
 */
static void
store_storefile(png_store *ps, png_uint_32 id)
{
   png_store_file *pf = voidcast(png_store_file*, malloc(sizeof *pf));
   if (pf == NULL)
      png_error(ps->pwrite, "storefile: OOM");
   safecat(pf->name, sizeof pf->name, 0, ps->wname);
   pf->id = id;
   pf->data = ps->new;
   pf->datacount = ps->writepos;
   ps->new.prev = NULL;
   ps->writepos = 0;
   pf->palette = ps->palette;
   pf->npalette = ps->npalette;
   ps->palette = 0;
   ps->npalette = 0;

   /* And save it. */
   pf->next = ps->saved;
   ps->saved = pf;
}

/* Generate an error message (in the given buffer) */
static size_t
store_message(png_store *ps, png_const_structp pp, char *buffer, size_t bufsize,
   size_t pos, PNG_CONST char *msg)
{
   if (pp != NULL && pp == ps->pread)
   {
      /* Reading a file */
      pos = safecat(buffer, bufsize, pos, "read: ");

      if (ps->current != NULL)
      {
         pos = safecat(buffer, bufsize, pos, ps->current->name);
         pos = safecat(buffer, bufsize, pos, sep);
      }
   }

   else if (pp != NULL && pp == ps->pwrite)
   {
      /* Writing a file */
      pos = safecat(buffer, bufsize, pos, "write: ");
      pos = safecat(buffer, bufsize, pos, ps->wname);
      pos = safecat(buffer, bufsize, pos, sep);
   }

   else
   {
      /* Neither reading nor writing (or a memory error in struct delete) */
      pos = safecat(buffer, bufsize, pos, "pngvalid: ");
   }

   if (ps->test[0] != 0)
   {
      pos = safecat(buffer, bufsize, pos, ps->test);
      pos = safecat(buffer, bufsize, pos, sep);
   }
   pos = safecat(buffer, bufsize, pos, msg);
   return pos;
}

/* Verbose output to the error stream: */
static void
store_verbose(png_store *ps, png_const_structp pp, png_const_charp prefix,
   png_const_charp message)
{
   char buffer[512];

   if (prefix)
      fputs(prefix, stderr);

   (void)store_message(ps, pp, buffer, sizeof buffer, 0, message);
   fputs(buffer, stderr);
   fputc('\n', stderr);
}

/* Log an error or warning - the relevant count is always incremented. */
static void
store_log(png_store* ps, png_const_structp pp, png_const_charp message,
   int is_error)
{
   /* The warning is copied to the error buffer if there are no errors and it is
    * the first warning.  The error is copied to the error buffer if it is the
    * first error (overwriting any prior warnings).
    */
   if (is_error ? (ps->nerrors)++ == 0 :
       (ps->nwarnings)++ == 0 && ps->nerrors == 0)
      store_message(ps, pp, ps->error, sizeof ps->error, 0, message);

   if (ps->verbose)
      store_verbose(ps, pp, is_error ? "error: " : "warning: ", message);
}

#ifdef PNG_READ_SUPPORTED
/* Internal error function, called with a png_store but no libpng stuff. */
static void
internal_error(png_store *ps, png_const_charp message)
{
   store_log(ps, NULL, message, 1 /* error */);

   /* And finally throw an exception. */
   {
      struct exception_context *the_exception_context = &ps->exception_context;
      Throw ps;
   }
}
#endif /* PNG_READ_SUPPORTED */

/* Functions to use as PNG callbacks. */
static void PNGCBAPI
store_error(png_structp ppIn, png_const_charp message) /* PNG_NORETURN */
{
   png_const_structp pp = ppIn;
   png_store *ps = voidcast(png_store*, png_get_error_ptr(pp));

   if (!ps->expect_error)
      store_log(ps, pp, message, 1 /* error */);

   /* And finally throw an exception. */
   {
      struct exception_context *the_exception_context = &ps->exception_context;
      Throw ps;
   }
}

static void PNGCBAPI
store_warning(png_structp ppIn, png_const_charp message)
{
   png_const_structp pp = ppIn;
   png_store *ps = voidcast(png_store*, png_get_error_ptr(pp));

   if (!ps->expect_warning)
      store_log(ps, pp, message, 0 /* warning */);
   else
      ps->saw_warning = 1;
}

/* These somewhat odd functions are used when reading an image to ensure that
 * the buffer is big enough, the png_structp is for errors.
 */
/* Return a single row from the correct image. */
static png_bytep
store_image_row(PNG_CONST png_store* ps, png_const_structp pp, int nImage,
   png_uint_32 y)
{
   png_size_t coffset = (nImage * ps->image_h + y) * (ps->cb_row + 5) + 2;

   if (ps->image == NULL)
      png_error(pp, "no allocated image");

   if (coffset + ps->cb_row + 3 > ps->cb_image)
      png_error(pp, "image too small");

   return ps->image + coffset;
}

static void
store_image_free(png_store *ps, png_const_structp pp)
{
   if (ps->image != NULL)
   {
      png_bytep image = ps->image;

      if (image[-1] != 0xed || image[ps->cb_image] != 0xfe)
      {
         if (pp != NULL)
            png_error(pp, "png_store image overwrite (1)");
         else
            store_log(ps, NULL, "png_store image overwrite (2)", 1);
      }

      ps->image = NULL;
      ps->cb_image = 0;
      --image;
      free(image);
   }
}

static void
store_ensure_image(png_store *ps, png_const_structp pp, int nImages,
   png_size_t cbRow, png_uint_32 cRows)
{
   png_size_t cb = nImages * cRows * (cbRow + 5);

   if (ps->cb_image < cb)
   {
      png_bytep image;

      store_image_free(ps, pp);

      /* The buffer is deliberately mis-aligned. */
      image = voidcast(png_bytep, malloc(cb+2));
      if (image == NULL)
      {
         /* Called from the startup - ignore the error for the moment. */
         if (pp == NULL)
            return;

         png_error(pp, "OOM allocating image buffer");
      }

      /* These magic tags are used to detect overwrites above. */
      ++image;
      image[-1] = 0xed;
      image[cb] = 0xfe;

      ps->image = image;
      ps->cb_image = cb;
   }

   /* We have an adequate sized image; lay out the rows.  There are 2 bytes at
    * the start and three at the end of each (this ensures that the row
    * alignment starts out odd - 2+1 and changes for larger images on each row.)
    */
   ps->cb_row = cbRow;
   ps->image_h = cRows;

   /* For error checking, the whole buffer is set to 10110010 (0xb2 - 178).
    * This deliberately doesn't match the bits in the size test image which are
    * outside the image; these are set to 0xff (all 1).  To make the row
    * comparison work in the 'size' test case the size rows are pre-initialized
    * to the same value prior to calling 'standard_row'.
    */
   memset(ps->image, 178, cb);

   /* Then put in the marks. */
   while (--nImages >= 0)
   {
      png_uint_32 y;

      for (y=0; y<cRows; ++y)
      {
         png_bytep row = store_image_row(ps, pp, nImages, y);

         /* The markers: */
         row[-2] = 190;
         row[-1] = 239;
         row[cbRow] = 222;
         row[cbRow+1] = 173;
         row[cbRow+2] = 17;
      }
   }
}

#ifdef PNG_READ_SUPPORTED
static void
store_image_check(PNG_CONST png_store* ps, png_const_structp pp, int iImage)
{
   png_const_bytep image = ps->image;

   if (image[-1] != 0xed || image[ps->cb_image] != 0xfe)
      png_error(pp, "image overwrite");
   else
   {
      png_size_t cbRow = ps->cb_row;
      png_uint_32 rows = ps->image_h;

      image += iImage * (cbRow+5) * ps->image_h;

      image += 2; /* skip image first row markers */

      while (rows-- > 0)
      {
         if (image[-2] != 190 || image[-1] != 239)
            png_error(pp, "row start overwritten");

         if (image[cbRow] != 222 || image[cbRow+1] != 173 ||
            image[cbRow+2] != 17)
            png_error(pp, "row end overwritten");

         image += cbRow+5;
      }
   }
}
#endif /* PNG_READ_SUPPORTED */

static void PNGCBAPI
store_write(png_structp ppIn, png_bytep pb, png_size_t st)
{
   png_const_structp pp = ppIn;
   png_store *ps = voidcast(png_store*, png_get_io_ptr(pp));

   if (ps->pwrite != pp)
      png_error(pp, "store state damaged");

   while (st > 0)
   {
      size_t cb;

      if (ps->writepos >= STORE_BUFFER_SIZE)
         store_storenew(ps);

      cb = st;

      if (cb > STORE_BUFFER_SIZE - ps->writepos)
         cb = STORE_BUFFER_SIZE - ps->writepos;

      memcpy(ps->new.buffer + ps->writepos, pb, cb);
      pb += cb;
      st -= cb;
      ps->writepos += cb;
   }
}

static void PNGCBAPI
store_flush(png_structp ppIn)
{
   UNUSED(ppIn) /*DOES NOTHING*/
}

#ifdef PNG_READ_SUPPORTED
static size_t
store_read_buffer_size(png_store *ps)
{
   /* Return the bytes available for read in the current buffer. */
   if (ps->next != &ps->current->data)
      return STORE_BUFFER_SIZE;

   return ps->current->datacount;
}

#ifdef PNG_READ_TRANSFORMS_SUPPORTED
/* Return total bytes available for read. */
static size_t
store_read_buffer_avail(png_store *ps)
{
   if (ps->current != NULL && ps->next != NULL)
   {
      png_store_buffer *next = &ps->current->data;
      size_t cbAvail = ps->current->datacount;

      while (next != ps->next && next != NULL)
      {
         next = next->prev;
         cbAvail += STORE_BUFFER_SIZE;
      }

      if (next != ps->next)
         png_error(ps->pread, "buffer read error");

      if (cbAvail > ps->readpos)
         return cbAvail - ps->readpos;
   }

   return 0;
}
#endif

static int
store_read_buffer_next(png_store *ps)
{
   png_store_buffer *pbOld = ps->next;
   png_store_buffer *pbNew = &ps->current->data;
   if (pbOld != pbNew)
   {
      while (pbNew != NULL && pbNew->prev != pbOld)
         pbNew = pbNew->prev;

      if (pbNew != NULL)
      {
         ps->next = pbNew;
         ps->readpos = 0;
         return 1;
      }

      png_error(ps->pread, "buffer lost");
   }

   return 0; /* EOF or error */
}

/* Need separate implementation and callback to allow use of the same code
 * during progressive read, where the io_ptr is set internally by libpng.
 */
static void
store_read_imp(png_store *ps, png_bytep pb, png_size_t st)
{
   if (ps->current == NULL || ps->next == NULL)
      png_error(ps->pread, "store state damaged");

   while (st > 0)
   {
      size_t cbAvail = store_read_buffer_size(ps) - ps->readpos;

      if (cbAvail > 0)
      {
         if (cbAvail > st) cbAvail = st;
         memcpy(pb, ps->next->buffer + ps->readpos, cbAvail);
         st -= cbAvail;
         pb += cbAvail;
         ps->readpos += cbAvail;
      }

      else if (!store_read_buffer_next(ps))
         png_error(ps->pread, "read beyond end of file");
   }
}

static void PNGCBAPI
store_read(png_structp ppIn, png_bytep pb, png_size_t st)
{
   png_const_structp pp = ppIn;
   png_store *ps = voidcast(png_store*, png_get_io_ptr(pp));

   if (ps == NULL || ps->pread != pp)
      png_error(pp, "bad store read call");

   store_read_imp(ps, pb, st);
}

static void
store_progressive_read(png_store *ps, png_structp pp, png_infop pi)
{
   /* Notice that a call to store_read will cause this function to fail because
    * readpos will be set.
    */
   if (ps->pread != pp || ps->current == NULL || ps->next == NULL)
      png_error(pp, "store state damaged (progressive)");

   do
   {
      if (ps->readpos != 0)
         png_error(pp, "store_read called during progressive read");

      png_process_data(pp, pi, ps->next->buffer, store_read_buffer_size(ps));
   }
   while (store_read_buffer_next(ps));
}
#endif /* PNG_READ_SUPPORTED */

/* The caller must fill this in: */
static store_palette_entry *
store_write_palette(png_store *ps, int npalette)
{
   if (ps->pwrite == NULL)
      store_log(ps, NULL, "attempt to write palette without write stream", 1);

   if (ps->palette != NULL)
      png_error(ps->pwrite, "multiple store_write_palette calls");

   /* This function can only return NULL if called with '0'! */
   if (npalette > 0)
   {
      ps->palette = voidcast(store_palette_entry*, malloc(npalette *
         sizeof *ps->palette));

      if (ps->palette == NULL)
         png_error(ps->pwrite, "store new palette: OOM");

      ps->npalette = npalette;
   }

   return ps->palette;
}

#ifdef PNG_READ_SUPPORTED
static store_palette_entry *
store_current_palette(png_store *ps, int *npalette)
{
   /* This is an internal error (the call has been made outside a read
    * operation.)
    */
   if (ps->current == NULL)
      store_log(ps, ps->pread, "no current stream for palette", 1);

   /* The result may be null if there is no palette. */
   *npalette = ps->current->npalette;
   return ps->current->palette;
}
#endif /* PNG_READ_SUPPORTED */

/***************************** MEMORY MANAGEMENT*** ***************************/
#ifdef PNG_USER_MEM_SUPPORTED
/* A store_memory is simply the header for an allocated block of memory.  The
 * pointer returned to libpng is just after the end of the header block, the
 * allocated memory is followed by a second copy of the 'mark'.
 */
typedef struct store_memory
{
   store_pool          *pool;    /* Originating pool */
   struct store_memory *next;    /* Singly linked list */
   png_alloc_size_t     size;    /* Size of memory allocated */
   png_byte             mark[4]; /* ID marker */
} store_memory;

/* Handle a fatal error in memory allocation.  This calls png_error if the
 * libpng struct is non-NULL, else it outputs a message and returns.  This means
 * that a memory problem while libpng is running will abort (png_error) the
 * handling of particular file while one in cleanup (after the destroy of the
 * struct has returned) will simply keep going and free (or attempt to free)
 * all the memory.
 */
static void
store_pool_error(png_store *ps, png_const_structp pp, PNG_CONST char *msg)
{
   if (pp != NULL)
      png_error(pp, msg);

   /* Else we have to do it ourselves.  png_error eventually calls store_log,
    * above.  store_log accepts a NULL png_structp - it just changes what gets
    * output by store_message.
    */
   store_log(ps, pp, msg, 1 /* error */);
}

static void
store_memory_free(png_const_structp pp, store_pool *pool, store_memory *memory)
{
   /* Note that pp may be NULL (see store_pool_delete below), the caller has
    * found 'memory' in pool->list *and* unlinked this entry, so this is a valid
    * pointer (for sure), but the contents may have been trashed.
    */
   if (memory->pool != pool)
      store_pool_error(pool->store, pp, "memory corrupted (pool)");

   else if (memcmp(memory->mark, pool->mark, sizeof memory->mark) != 0)
      store_pool_error(pool->store, pp, "memory corrupted (start)");

   /* It should be safe to read the size field now. */
   else
   {
      png_alloc_size_t cb = memory->size;

      if (cb > pool->max)
         store_pool_error(pool->store, pp, "memory corrupted (size)");

      else if (memcmp((png_bytep)(memory+1)+cb, pool->mark, sizeof pool->mark)
         != 0)
         store_pool_error(pool->store, pp, "memory corrupted (end)");

      /* Finally give the library a chance to find problems too: */
      else
         {
         pool->current -= cb;
         free(memory);
         }
   }
}

static void
store_pool_delete(png_store *ps, store_pool *pool)
{
   if (pool->list != NULL)
   {
      fprintf(stderr, "%s: %s %s: memory lost (list follows):\n", ps->test,
         pool == &ps->read_memory_pool ? "read" : "write",
         pool == &ps->read_memory_pool ? (ps->current != NULL ?
            ps->current->name : "unknown file") : ps->wname);
      ++ps->nerrors;

      do
      {
         store_memory *next = pool->list;
         pool->list = next->next;
         next->next = NULL;

         fprintf(stderr, "\t%lu bytes @ %p\n",
             (unsigned long)next->size, (PNG_CONST void*)(next+1));
         /* The NULL means this will always return, even if the memory is
          * corrupted.
          */
         store_memory_free(NULL, pool, next);
      }
      while (pool->list != NULL);
   }

   /* And reset the other fields too for the next time. */
   if (pool->max > pool->max_max) pool->max_max = pool->max;
   pool->max = 0;
   if (pool->current != 0) /* unexpected internal error */
      fprintf(stderr, "%s: %s %s: memory counter mismatch (internal error)\n",
         ps->test, pool == &ps->read_memory_pool ? "read" : "write",
         pool == &ps->read_memory_pool ? (ps->current != NULL ?
            ps->current->name : "unknown file") : ps->wname);
   pool->current = 0;

   if (pool->limit > pool->max_limit)
      pool->max_limit = pool->limit;

   pool->limit = 0;

   if (pool->total > pool->max_total)
      pool->max_total = pool->total;

   pool->total = 0;

   /* Get a new mark too. */
   store_pool_mark(pool->mark);
}

/* The memory callbacks: */
static png_voidp PNGCBAPI
store_malloc(png_structp ppIn, png_alloc_size_t cb)
{
   png_const_structp pp = ppIn;
   store_pool *pool = voidcast(store_pool*, png_get_mem_ptr(pp));
   store_memory *new = voidcast(store_memory*, malloc(cb + (sizeof *new) +
      (sizeof pool->mark)));

   if (new != NULL)
   {
      if (cb > pool->max)
         pool->max = cb;

      pool->current += cb;

      if (pool->current > pool->limit)
         pool->limit = pool->current;

      pool->total += cb;

      new->size = cb;
      memcpy(new->mark, pool->mark, sizeof new->mark);
      memcpy((png_byte*)(new+1) + cb, pool->mark, sizeof pool->mark);
      new->pool = pool;
      new->next = pool->list;
      pool->list = new;
      ++new;
   }

   else
   {
      /* NOTE: the PNG user malloc function cannot use the png_ptr it is passed
       * other than to retrieve the allocation pointer!  libpng calls the
       * store_malloc callback in two basic cases:
       *
       * 1) From png_malloc; png_malloc will do a png_error itself if NULL is
       *    returned.
       * 2) From png_struct or png_info structure creation; png_malloc is
       *    to return so cleanup can be performed.
       *
       * To handle this store_malloc can log a message, but can't do anything
       * else.
       */
      store_log(pool->store, pp, "out of memory", 1 /* is_error */);
   }

   return new;
}

static void PNGCBAPI
store_free(png_structp ppIn, png_voidp memory)
{
   png_const_structp pp = ppIn;
   store_pool *pool = voidcast(store_pool*, png_get_mem_ptr(pp));
   store_memory *this = voidcast(store_memory*, memory), **test;

   /* Because libpng calls store_free with a dummy png_struct when deleting
    * png_struct or png_info via png_destroy_struct_2 it is necessary to check
    * the passed in png_structp to ensure it is valid, and not pass it to
    * png_error if it is not.
    */
   if (pp != pool->store->pread && pp != pool->store->pwrite)
      pp = NULL;

   /* First check that this 'memory' really is valid memory - it must be in the
    * pool list.  If it is, use the shared memory_free function to free it.
    */
   --this;
   for (test = &pool->list; *test != this; test = &(*test)->next)
   {
      if (*test == NULL)
      {
         store_pool_error(pool->store, pp, "bad pointer to free");
         return;
      }
   }

   /* Unlink this entry, *test == this. */
   *test = this->next;
   this->next = NULL;
   store_memory_free(pp, pool, this);
}
#endif /* PNG_USER_MEM_SUPPORTED */

/* Setup functions. */
/* Cleanup when aborting a write or after storing the new file. */
static void
store_write_reset(png_store *ps)
{
   if (ps->pwrite != NULL)
   {
      anon_context(ps);

      Try
         png_destroy_write_struct(&ps->pwrite, &ps->piwrite);

      Catch_anonymous
      {
         /* memory corruption: continue. */
      }

      ps->pwrite = NULL;
      ps->piwrite = NULL;
   }

   /* And make sure that all the memory has been freed - this will output
    * spurious errors in the case of memory corruption above, but this is safe.
    */
#  ifdef PNG_USER_MEM_SUPPORTED
      store_pool_delete(ps, &ps->write_memory_pool);
#  endif

   store_freenew(ps);
}

/* The following is the main write function, it returns a png_struct and,
 * optionally, a png_info suitable for writiing a new PNG file.  Use
 * store_storefile above to record this file after it has been written.  The
 * returned libpng structures as destroyed by store_write_reset above.
 */
static png_structp
set_store_for_write(png_store *ps, png_infopp ppi,
   PNG_CONST char * volatile name)
{
   anon_context(ps);

   Try
   {
      if (ps->pwrite != NULL)
         png_error(ps->pwrite, "write store already in use");

      store_write_reset(ps);
      safecat(ps->wname, sizeof ps->wname, 0, name);

      /* Don't do the slow memory checks if doing a speed test, also if user
       * memory is not supported we can't do it anyway.
       */
#     ifdef PNG_USER_MEM_SUPPORTED
         if (!ps->speed)
            ps->pwrite = png_create_write_struct_2(PNG_LIBPNG_VER_STRING,
               ps, store_error, store_warning, &ps->write_memory_pool,
               store_malloc, store_free);

         else
#     endif
         ps->pwrite = png_create_write_struct(png_get_libpng_ver(NULL),
            ps, store_error, store_warning);

      png_set_write_fn(ps->pwrite, ps, store_write, store_flush);

#     ifdef PNG_SET_OPTION_SUPPORTED
         {
            int opt;
            for (opt=0; opt<ps->noptions; ++opt)
               if (png_set_option(ps->pwrite, ps->options[opt].option,
                  ps->options[opt].setting) == PNG_OPTION_INVALID)
                  png_error(ps->pwrite, "png option invalid");
         }
#     endif

      if (ppi != NULL)
         *ppi = ps->piwrite = png_create_info_struct(ps->pwrite);
   }

   Catch_anonymous
      return NULL;

   return ps->pwrite;
}

/* Cleanup when finished reading (either due to error or in the success case).
 * This routine exists even when there is no read support to make the code
 * tidier (avoid a mass of ifdefs) and so easier to maintain.
 */
static void
store_read_reset(png_store *ps)
{
#  ifdef PNG_READ_SUPPORTED
      if (ps->pread != NULL)
      {
         anon_context(ps);

         Try
            png_destroy_read_struct(&ps->pread, &ps->piread, NULL);

         Catch_anonymous
         {
            /* error already output: continue */
         }

         ps->pread = NULL;
         ps->piread = NULL;
      }
#  endif

#  ifdef PNG_USER_MEM_SUPPORTED
      /* Always do this to be safe. */
      store_pool_delete(ps, &ps->read_memory_pool);
#  endif

   ps->current = NULL;
   ps->next = NULL;
   ps->readpos = 0;
   ps->validated = 0;
}

#ifdef PNG_READ_SUPPORTED
static void
store_read_set(png_store *ps, png_uint_32 id)
{
   png_store_file *pf = ps->saved;

   while (pf != NULL)
   {
      if (pf->id == id)
      {
         ps->current = pf;
         ps->next = NULL;
         store_read_buffer_next(ps);
         return;
      }

      pf = pf->next;
   }

   {
      size_t pos;
      char msg[FILE_NAME_SIZE+64];

      pos = standard_name_from_id(msg, sizeof msg, 0, id);
      pos = safecat(msg, sizeof msg, pos, ": file not found");
      png_error(ps->pread, msg);
   }
}

/* The main interface for reading a saved file - pass the id number of the file
 * to retrieve.  Ids must be unique or the earlier file will be hidden.  The API
 * returns a png_struct and, optionally, a png_info.  Both of these will be
 * destroyed by store_read_reset above.
 */
static png_structp
set_store_for_read(png_store *ps, png_infopp ppi, png_uint_32 id,
   PNG_CONST char *name)
{
   /* Set the name for png_error */
   safecat(ps->test, sizeof ps->test, 0, name);

   if (ps->pread != NULL)
      png_error(ps->pread, "read store already in use");

   store_read_reset(ps);

   /* Both the create APIs can return NULL if used in their default mode
    * (because there is no other way of handling an error because the jmp_buf
    * by default is stored in png_struct and that has not been allocated!)
    * However, given that store_error works correctly in these circumstances
    * we don't ever expect NULL in this program.
    */
#  ifdef PNG_USER_MEM_SUPPORTED
      if (!ps->speed)
         ps->pread = png_create_read_struct_2(PNG_LIBPNG_VER_STRING, ps,
             store_error, store_warning, &ps->read_memory_pool, store_malloc,
             store_free);

      else
#  endif
   ps->pread = png_create_read_struct(PNG_LIBPNG_VER_STRING, ps, store_error,
      store_warning);

   if (ps->pread == NULL)
   {
      struct exception_context *the_exception_context = &ps->exception_context;

      store_log(ps, NULL, "png_create_read_struct returned NULL (unexpected)",
         1 /*error*/);

      Throw ps;
   }

#  ifdef PNG_SET_OPTION_SUPPORTED
      {
         int opt;
         for (opt=0; opt<ps->noptions; ++opt)
            if (png_set_option(ps->pread, ps->options[opt].option,
               ps->options[opt].setting) == PNG_OPTION_INVALID)
                  png_error(ps->pread, "png option invalid");
      }
#  endif

   store_read_set(ps, id);

   if (ppi != NULL)
      *ppi = ps->piread = png_create_info_struct(ps->pread);

   return ps->pread;
}
#endif /* PNG_READ_SUPPORTED */

/* The overall cleanup of a store simply calls the above then removes all the
 * saved files.  This does not delete the store itself.
 */
static void
store_delete(png_store *ps)
{
   store_write_reset(ps);
   store_read_reset(ps);
   store_freefile(&ps->saved);
   store_image_free(ps, NULL);
}

/*********************** PNG FILE MODIFICATION ON READ ************************/
/* Files may be modified on read.  The following structure contains a complete
 * png_store together with extra members to handle modification and a special
 * read callback for libpng.  To use this the 'modifications' field must be set
 * to a list of png_modification structures that actually perform the
 * modification, otherwise a png_modifier is functionally equivalent to a
 * png_store.  There is a special read function, set_modifier_for_read, which
 * replaces set_store_for_read.
 */
typedef enum modifier_state
{
   modifier_start,                        /* Initial value */
   modifier_signature,                    /* Have a signature */
   modifier_IHDR                          /* Have an IHDR */
} modifier_state;

typedef struct CIE_color
{
   /* A single CIE tristimulus value, representing the unique response of a
    * standard observer to a variety of light spectra.  The observer recognizes
    * all spectra that produce this response as the same color, therefore this
    * is effectively a description of a color.
    */
  …