Check libpng directly into third_party/

third_party/libpng/contrib/libtests/pngimage.c

+/* pngimage.c
+ *
+ * Copyright (c) 2015,2016 John Cunningham Bowler
+ *
+ * Last changed in libpng 1.6.22 [(PENDING RELEASE)]
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ *
+ * Test the png_read_png and png_write_png interfaces.  Given a PNG file load it
+ * using png_read_png and then write with png_write_png.  Test all possible
+ * transforms.
+ */
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <stdio.h>
+#include <assert.h>
+
+#if defined(HAVE_CONFIG_H) && !defined(PNG_NO_CONFIG_H)
+#  include <config.h>
+#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
+
+#ifndef PNG_SETJMP_SUPPORTED
+#  include <setjmp.h> /* because png.h did *not* include this */
+#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 && defined(HAVE_CONFIG_H)
+#  define SKIP 77
+#else
+#  define SKIP 0
+#endif
+
+#if defined(PNG_INFO_IMAGE_SUPPORTED) && defined(PNG_SEQUENTIAL_READ_SUPPORTED)\
+    && (defined(PNG_READ_PNG_SUPPORTED) || PNG_LIBPNG_VER < 10700)
+/* If a transform is valid on both read and write this implies that if the
+ * transform is applied to read it must also be applied on write to produce
+ * meaningful data.  This is because these transforms when performed on read
+ * produce data with a memory format that does not correspond to a PNG format.
+ *
+ * Most of these transforms are invertible; after applying the transform on
+ * write the result is the original PNG data that would have would have been
+ * read if no transform were applied.
+ *
+ * The exception is _SHIFT, which destroys the low order bits marked as not
+ * significant in a PNG with the sBIT chunk.
+ *
+ * The following table lists, for each transform, the conditions under which it
+ * is expected to do anything.  Conditions are defined as follows:
+ *
+ * 1) Color mask bits required - simply a mask to AND with color_type; one of
+ *    these must be present for the transform to fire, except that 0 means
+ *    'always'.
+ * 2) Color mask bits which must be absent - another mask - none of these must
+ *    be present.
+ * 3) Bit depths - a mask of component bit depths for the transform to fire.
+ * 4) 'read' - the transform works in png_read_png.
+ * 5) 'write' - the transform works in png_write_png.
+ * 6) PNG_INFO_chunk; a mask of the chunks that must be present for the
+ *    transform to fire.  All must be present - the requirement is that
+ *    png_get_valid() & mask == mask, so if mask is 0 there is no requirement.
+ *
+ * The condition refers to the original image state - if multiple transforms are
+ * used together it is possible to cause a transform that wouldn't fire on the
+ * original image to fire.
+ */
+static struct transform_info
+{
+   const char *name;
+   int         transform;
+   png_uint_32 valid_chunks;
+#     define CHUNK_NONE 0
+#     define CHUNK_sBIT PNG_INFO_sBIT
+#     define CHUNK_tRNS PNG_INFO_tRNS
+   png_byte    color_mask_required;
+   png_byte    color_mask_absent;
+#     define COLOR_MASK_X   0
+#     define COLOR_MASK_P   PNG_COLOR_MASK_PALETTE
+#     define COLOR_MASK_C   PNG_COLOR_MASK_COLOR
+#     define COLOR_MASK_A   PNG_COLOR_MASK_ALPHA
+#     define COLOR_MASK_ALL (PALETTE+COLOR+ALPHA)  /* absent = gray, no alpha */
+   png_byte    bit_depths;
+#     define BD_ALL  (1 + 2 + 4 + 8 + 16)
+#     define BD_PAL  (1 + 2 + 4 + 8)
+#     define BD_LOW  (1 + 2 + 4)
+#     define BD_16   16
+#     define BD_TRUE (8+16) /* i.e. true-color depths */
+   png_byte    when;
+#     define TRANSFORM_R  1
+#     define TRANSFORM_W  2
+#     define TRANSFORM_RW 3
+   png_byte    tested; /* the transform was tested somewhere */
+} transform_info[] =
+{
+   /* List ALL the PNG_TRANSFORM_ macros here.  Check for support using the READ
+    * macros; even if the transform is supported on write it cannot be tested
+    * without the read support.
+    */
+#  define T(name,chunk,cm_required,cm_absent,bd,when)\
+   {  #name, PNG_TRANSFORM_ ## name, CHUNK_ ## chunk,\
+      COLOR_MASK_ ## cm_required, COLOR_MASK_ ## cm_absent, BD_ ## bd,\
+      TRANSFORM_ ## when, 0/*!tested*/ }
+
+#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+   T(STRIP_16,            NONE, X,   X,   16,  R),
+      /* drops the bottom 8 bits when bit depth is 16 */
+#endif
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+   T(STRIP_ALPHA,         NONE, A,   X,  ALL,  R),
+      /* removes the alpha channel if present */
+#endif
+#ifdef PNG_WRITE_PACK_SUPPORTED
+#  define TRANSFORM_RW_PACK TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_PACK TRANSFORM_R
+#endif
+#ifdef PNG_READ_PACK_SUPPORTED
+   T(PACKING,             NONE, X,   X,  LOW, RW_PACK),
+      /* unpacks low-bit-depth components into 1 byte per component on read,
+       * reverses this on write.
+       */
+#endif
+#ifdef PNG_WRITE_PACKSWAP_SUPPORTED
+#  define TRANSFORM_RW_PACKSWAP TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_PACKSWAP TRANSFORM_R
+#endif
+#ifdef PNG_READ_PACKSWAP_SUPPORTED
+   T(PACKSWAP,            NONE, X,   X,  LOW, RW_PACKSWAP),
+      /* reverses the order of low-bit-depth components packed into a byte */
+#endif
+#ifdef PNG_READ_EXPAND_SUPPORTED
+   T(EXPAND,              NONE, P,   X,  ALL,  R),
+      /* expands PLTE PNG files to RGB (no tRNS) or RGBA (tRNS) *
+       * Note that the 'EXPAND' transform does lots of different things: */
+   T(EXPAND,              NONE, X,   C,  ALL,  R),
+      /* expands grayscale PNG files to RGB, or RGBA */
+   T(EXPAND,              tRNS, X,   A,  ALL,  R),
+      /* expands the tRNS chunk in files without alpha */
+#endif
+#ifdef PNG_WRITE_INVERT_SUPPORTED
+#  define TRANSFORM_RW_INVERT TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_INVERT TRANSFORM_R
+#endif
+#ifdef PNG_READ_INVERT_SUPPORTED
+   T(INVERT_MONO,         NONE, X,   C,  ALL, RW_INVERT),
+      /* converts gray-scale components to 1..0 from 0..1 */
+#endif
+#ifdef PNG_WRITE_SHIFT_SUPPORTED
+#  define TRANSFORM_RW_SHIFT TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_SHIFT TRANSFORM_R
+#endif
+#ifdef PNG_READ_SHIFT_SUPPORTED
+   T(SHIFT,               sBIT, X,   X,  ALL, RW_SHIFT),
+      /* reduces component values to the original range based on the sBIT chunk,
+       * this is only partially reversible - the low bits are lost and cannot be
+       * recovered on write.  In fact write code replicates the bits to generate
+       * new low-order bits.
+       */
+#endif
+#ifdef PNG_WRITE_BGR_SUPPORTED
+#  define TRANSFORM_RW_BGR TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_BGR TRANSFORM_R
+#endif
+#ifdef PNG_READ_BGR_SUPPORTED
+   T(BGR,                 NONE, C,   P, TRUE, RW_BGR),
+      /* reverses the rgb component values of true-color pixels */
+#endif
+#ifdef PNG_WRITE_SWAP_ALPHA_SUPPORTED
+#  define TRANSFORM_RW_SWAP_ALPHA TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_SWAP_ALPHA TRANSFORM_R
+#endif
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
+   T(SWAP_ALPHA,          NONE, A,   X, TRUE, RW_SWAP_ALPHA),
+      /* swaps the alpha channel of RGBA or GA pixels to the front - ARGB or
+       * AG, on write reverses the process.
+       */
+#endif
+#ifdef PNG_WRITE_SWAP_SUPPORTED
+#  define TRANSFORM_RW_SWAP TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_SWAP TRANSFORM_R
+#endif
+#ifdef PNG_READ_SWAP_SUPPORTED
+   T(SWAP_ENDIAN,         NONE, X,   P,   16, RW_SWAP),
+      /* byte-swaps 16-bit component values */
+#endif
+#ifdef PNG_WRITE_INVERT_ALPHA_SUPPORTED
+#  define TRANSFORM_RW_INVERT_ALPHA TRANSFORM_RW
+#else
+#  define TRANSFORM_RW_INVERT_ALPHA TRANSFORM_R
+#endif
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
+   T(INVERT_ALPHA,        NONE, A,   X, TRUE, RW_INVERT_ALPHA),
+      /* converts an alpha channel from 0..1 to 1..0 */
+#endif
+#ifdef PNG_WRITE_FILLER_SUPPORTED
+   T(STRIP_FILLER_BEFORE, NONE, A,   P, TRUE,  W), /* 'A' for a filler! */
+      /* on write skips a leading filler channel; testing requires data with a
+       * filler channel so this is produced from RGBA or GA images by removing
+       * the 'alpha' flag from the color type in place.
+       */
+   T(STRIP_FILLER_AFTER,  NONE, A,   P, TRUE,  W),
+      /* on write strips a trailing filler channel */
+#endif
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+   T(GRAY_TO_RGB,         NONE, X,   C,  ALL,  R),
+      /* expands grayscale images to RGB, also causes the palette part of
+       * 'EXPAND' to happen.  Low bit depth grayscale images are expanded to
+       * 8-bits per component and no attempt is made to convert the image to a
+       * palette image.  While this transform is partially reversible
+       * png_write_png does not currently support this.
+       */
+   T(GRAY_TO_RGB,         NONE, P,   X,  ALL,  R),
+      /* The 'palette' side effect mentioned above; a bit bogus but this is the
+       * way the libpng code works.
+       */
+#endif
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+   T(EXPAND_16,           NONE, X,   X,  PAL,  R),
+      /* expands images to 16-bits per component, as a side effect expands
+       * palette images to RGB and expands the tRNS chunk if present, so it can
+       * modify 16-bit per component images as well:
+       */
+   T(EXPAND_16,           tRNS, X,   A,   16,  R),
+      /* side effect of EXPAND_16 - expands the tRNS chunk in an RGB or G 16-bit
+       * image.
+       */
+#endif
+#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+   T(SCALE_16,            NONE, X,   X,   16,  R),
+      /* scales 16-bit components to 8-bits. */
+#endif
+
+   { NULL /*name*/, 0, 0, 0, 0, 0, 0, 0/*!tested*/ }
+
+#undef T
+};
+
+#define ARRAY_SIZE(a) ((sizeof a)/(sizeof a[0]))
+#define TTABLE_SIZE ARRAY_SIZE(transform_info)
+
+/* Some combinations of options that should be reversible are not; these cases
+ * are bugs.
+ */
+static int known_bad_combos[][2] =
+{
+   /* problem, antidote */
+   { PNG_TRANSFORM_SHIFT | PNG_TRANSFORM_INVERT_ALPHA, 0/*antidote*/ }
+};
+
+static int
+is_combo(int transforms)
+{
+   return transforms & (transforms-1); /* non-zero if more than one set bit */
+}
+
+static int
+first_transform(int transforms)
+{
+   return transforms & -transforms; /* lowest set bit */
+}
+
+static int
+is_bad_combo(int transforms)
+{
+   unsigned int i;
+
+   for (i=0; i<ARRAY_SIZE(known_bad_combos); ++i)
+   {
+      int combo = known_bad_combos[i][0];
+
+      if ((combo & transforms) == combo &&
+         (transforms & known_bad_combos[i][1]) == 0)
+         return 1;
+   }
+
+   return 0; /* combo is ok */
+}
+
+static const char *
+transform_name(int t)
+   /* The name, if 't' has multiple bits set the name of the lowest set bit is
+    * returned.
+    */
+{
+   unsigned int i;
+
+   t &= -t; /* first set bit */
+
+   for (i=0; i<TTABLE_SIZE; ++i) if (transform_info[i].name != NULL)
+   {
+      if ((transform_info[i].transform & t) != 0)
+         return transform_info[i].name;
+   }
+
+   return "invalid transform";
+}
+
+/* Variables calculated by validate_T below and used to record all the supported
+ * transforms.  Need (unsigned int) here because of the places where these
+ * values are used (unsigned compares in the 'exhaustive' iterator.)
+ */
+static unsigned int read_transforms, write_transforms, rw_transforms;
+
+static void
+validate_T(void)
+   /* Validate the above table - this just builds the above values */
+{
+   unsigned int i;
+
+   for (i=0; i<TTABLE_SIZE; ++i) if (transform_info[i].name != NULL)
+   {
+      if (transform_info[i].when & TRANSFORM_R)
+         read_transforms |= transform_info[i].transform;
+
+      if (transform_info[i].when & TRANSFORM_W)
+         write_transforms |= transform_info[i].transform;
+   }
+
+   /* Reversible transforms are those which are supported on both read and
+    * write.
+    */
+   rw_transforms = read_transforms & write_transforms;
+}
+
+/* FILE DATA HANDLING
+ *    The original file is cached in memory.  During write the output file is
+ *    written to memory.
+ *
+ *    In both cases the file data is held in a linked list of buffers - not all
+ *    of these are in use at any time.
+ */
+#define NEW(type) ((type *)malloc(sizeof (type)))
+#define DELETE(ptr) (free(ptr))
+
+struct buffer_list
+{
+   struct buffer_list *next;         /* next buffer in list */
+   png_byte            buffer[1024]; /* the actual buffer */
+};
+
+struct buffer
+{
+   struct buffer_list  *last;       /* last buffer in use */
+   size_t               end_count;  /* bytes in the last buffer */
+   struct buffer_list  *current;    /* current buffer being read */
+   size_t               read_count; /* count of bytes read from current */
+   struct buffer_list   first;      /* the very first buffer */
+};
+
+static void
+buffer_init(struct buffer *buffer)
+   /* Call this only once for a given buffer */
+{
+   buffer->first.next = NULL;
+   buffer->last = NULL;
+   buffer->current = NULL;
+}
+
+static void
+buffer_destroy_list(struct buffer_list *list)
+{
+   if (list != NULL)
+   {
+      struct buffer_list *next = list->next;
+      DELETE(list);
+      buffer_destroy_list(next);
+   }
+}
+
+static void
+buffer_destroy(struct buffer *buffer)
+{
+   struct buffer_list *list = buffer->first.next;
+   buffer_init(buffer);
+   buffer_destroy_list(list);
+}
+
+#ifdef PNG_WRITE_SUPPORTED
+static void
+buffer_start_write(struct buffer *buffer)
+{
+   buffer->last = &buffer->first;
+   buffer->end_count = 0;
+   buffer->current = NULL;
+}
+#endif
+
+static void
+buffer_start_read(struct buffer *buffer)
+{
+   buffer->current = &buffer->first;
+   buffer->read_count = 0;
+}
+
+#ifdef ENOMEM /* required by POSIX 1003.1 */
+#  define MEMORY ENOMEM
+#else
+#  define MEMORY ERANGE /* required by ANSI-C */
+#endif
+static struct buffer *
+get_buffer(png_structp pp)
+   /* Used from libpng callbacks to get the current buffer */
+{
+   return (struct buffer*)png_get_io_ptr(pp);
+}
+
+static struct buffer_list *
+buffer_extend(struct buffer_list *current)
+{
+   struct buffer_list *add;
+
+   assert(current->next == NULL);
+
+   add = NEW(struct buffer_list);
+   if (add == NULL)
+      return NULL;
+
+   add->next = NULL;
+   current->next = add;
+
+   return add;
+}
+
+/* Load a buffer from a file; does the equivalent of buffer_start_write.  On a
+ * read error returns an errno value, else returns 0.
+ */
+static int
+buffer_from_file(struct buffer *buffer, FILE *fp)
+{
+   struct buffer_list *last = &buffer->first;
+   size_t count = 0;
+
+   for (;;)
+   {
+      size_t r = fread(last->buffer+count, 1/*size*/,
+         (sizeof last->buffer)-count, fp);
+
+      if (r > 0)
+      {
+         count += r;
+
+         if (count >= sizeof last->buffer)
+         {
+            assert(count == sizeof last->buffer);
+            count = 0;
+
+            if (last->next == NULL)
+            {
+               last = buffer_extend(last);
+               if (last == NULL)
+                  return MEMORY;
+            }
+
+            else
+               last = last->next;
+         }
+      }
+
+      else /* fread failed - probably end of file */
+      {
+         if (feof(fp))
+         {
+            buffer->last = last;
+            buffer->end_count = count;
+            return 0; /* no error */
+         }
+
+         /* Some kind of funky error; errno should be non-zero */
+         return errno == 0 ? ERANGE : errno;
+      }
+   }
+}
+
+/* This structure is used to control the test of a single file. */
+typedef enum
+{
+   VERBOSE,        /* switches on all messages */
+   INFORMATION,
+   WARNINGS,       /* switches on warnings */
+   LIBPNG_WARNING,
+   APP_WARNING,
+   ERRORS,         /* just errors */
+   APP_FAIL,       /* continuable error - no need to longjmp */
+   LIBPNG_ERROR,   /* this and higher cause a longjmp */
+   LIBPNG_BUG,     /* erroneous behavior in libpng */
+   APP_ERROR,      /* such as out-of-memory in a callback */
+   QUIET,          /* no normal messages */
+   USER_ERROR,     /* such as file-not-found */
+   INTERNAL_ERROR
+} error_level;
+#define LEVEL_MASK      0xf   /* where the level is in 'options' */
+
+#define EXHAUSTIVE      0x010 /* Test all combinations of active options */
+#define STRICT          0x020 /* Fail on warnings as well as errors */
+#define LOG             0x040 /* Log pass/fail to stdout */
+#define CONTINUE        0x080 /* Continue on APP_FAIL errors */
+#define SKIP_BUGS       0x100 /* Skip over known bugs */
+#define LOG_SKIPPED     0x200 /* Log skipped bugs */
+#define FIND_BAD_COMBOS 0x400 /* Attempt to deduce bad combos */
+#define LIST_COMBOS     0x800 /* List combos by name */
+
+/* Result masks apply to the result bits in the 'results' field below; these
+ * bits are simple 1U<<error_level.  A pass requires either nothing worse than
+ * warnings (--relaxes) or nothing worse than information (--strict)
+ */
+#define RESULT_STRICT(r)   (((r) & ~((1U<<WARNINGS)-1)) == 0)
+#define RESULT_RELAXED(r)  (((r) & ~((1U<<ERRORS)-1)) == 0)
+
+struct display
+{
+   jmp_buf        error_return;      /* Where to go to on error */
+
+   const char    *filename;          /* The name of the original file */
+   const char    *operation;         /* Operation being performed */
+   int            transforms;        /* Transform used in operation */
+   png_uint_32    options;           /* See display_log below */
+   png_uint_32    results;           /* A mask of errors seen */
+
+
+   png_structp    original_pp;       /* used on the original read */
+   png_infop      original_ip;       /* set by the original read */
+
+   png_size_t     original_rowbytes; /* of the original rows: */
+   png_bytepp     original_rows;     /* from the original read */
+
+   /* Original chunks valid */
+   png_uint_32    chunks;
+
+   /* Original IHDR information */
+   png_uint_32    width;
+   png_uint_32    height;
+   int            bit_depth;
+   int            color_type;
+   int            interlace_method;
+   int            compression_method;
+   int            filter_method;
+
+   /* Derived information for the original image. */
+   int            active_transforms;  /* transforms that do something on read */
+   int            ignored_transforms; /* transforms that should do nothing */
+
+   /* Used on a read, both the original read and when validating a written
+    * image.
+    */
+   png_structp    read_pp;
+   png_infop      read_ip;
+
+#  ifdef PNG_WRITE_SUPPORTED
+      /* Used to write a new image (the original info_ptr is used) */
+      png_structp   write_pp;
+      struct buffer written_file;   /* where the file gets written */
+#  endif
+
+   struct buffer  original_file;     /* Data read from the original file */
+};
+
+static void
+display_init(struct display *dp)
+   /* Call this only once right at the start to initialize the control
+    * structure, the (struct buffer) lists are maintained across calls - the
+    * memory is not freed.
+    */
+{
+   memset(dp, 0, sizeof *dp);
+   dp->options = WARNINGS; /* default to !verbose, !quiet */
+   dp->filename = NULL;
+   dp->operation = NULL;
+   dp->original_pp = NULL;
+   dp->original_ip = NULL;
+   dp->original_rows = NULL;
+   dp->read_pp = NULL;
+   dp->read_ip = NULL;
+   buffer_init(&dp->original_file);
+
+#  ifdef PNG_WRITE_SUPPORTED
+      dp->write_pp = NULL;
+      buffer_init(&dp->written_file);
+#  endif
+}
+
+static void
+display_clean_read(struct display *dp)
+{
+   if (dp->read_pp != NULL)
+      png_destroy_read_struct(&dp->read_pp, &dp->read_ip, NULL);
+}
+
+#ifdef PNG_WRITE_SUPPORTED
+static void
+display_clean_write(struct display *dp)
+{
+      if (dp->write_pp != NULL)
+         png_destroy_write_struct(&dp->write_pp, NULL);
+}
+#endif
+
+static void
+display_clean(struct display *dp)
+{
+#  ifdef PNG_WRITE_SUPPORTED
+      display_clean_write(dp);
+#  endif
+   display_clean_read(dp);
+
+   dp->original_rowbytes = 0;
+   dp->original_rows = NULL;
+   dp->chunks = 0;
+
+   png_destroy_read_struct(&dp->original_pp, &dp->original_ip, NULL);
+   /* leave the filename for error detection */
+   dp->results = 0; /* reset for next time */
+}
+
+static void
+display_destroy(struct display *dp)
+{
+    /* Release any memory held in the display. */
+#  ifdef PNG_WRITE_SUPPORTED
+      buffer_destroy(&dp->written_file);
+#  endif
+
+   buffer_destroy(&dp->original_file);
+}
+
+static struct display *
+get_dp(png_structp pp)
+   /* The display pointer is always stored in the png_struct error pointer */
+{
+   struct display *dp = (struct display*)png_get_error_ptr(pp);
+
+   if (dp == NULL)
+   {
+      fprintf(stderr, "pngimage: internal error (no display)\n");
+      exit(99); /* prevents a crash */
+   }
+
+   return dp;
+}
+
+/* error handling */
+#ifdef __GNUC__
+#  define VGATTR __attribute__((__format__ (__printf__,3,4)))
+   /* Required to quiet GNUC warnings when the compiler sees a stdarg function
+    * that calls one of the stdio v APIs.
+    */
+#else
+#  define VGATTR
+#endif
+static void VGATTR
+display_log(struct display *dp, error_level level, const char *fmt, ...)
+   /* 'level' is as above, fmt is a stdio style format string.  This routine
+    * does not return if level is above LIBPNG_WARNING
+    */
+{
+   dp->results |= 1U << level;
+
+   if (level > (error_level)(dp->options & LEVEL_MASK))
+   {
+      const char *lp;
+      va_list ap;
+
+      switch (level)
+      {
+         case INFORMATION:    lp = "information"; break;
+         case LIBPNG_WARNING: lp = "warning(libpng)"; break;
+         case APP_WARNING:    lp = "warning(pngimage)"; break;
+         case APP_FAIL:       lp = "error(continuable)"; break;
+         case LIBPNG_ERROR:   lp = "error(libpng)"; break;
+         case LIBPNG_BUG:     lp = "bug(libpng)"; break;
+         case APP_ERROR:      lp = "error(pngimage)"; break;
+         case USER_ERROR:     lp = "error(user)"; break;
+
+         case INTERNAL_ERROR: /* anything unexpected is an internal error: */
+         case VERBOSE: case WARNINGS: case ERRORS: case QUIET:
+         default:             lp = "bug(pngimage)"; break;
+      }
+
+      fprintf(stderr, "%s: %s: %s",
+         dp->filename != NULL ? dp->filename : "<stdin>", lp, dp->operation);
+
+      if (dp->transforms != 0)
+      {
+         int tr = dp->transforms;
+
+         if (is_combo(tr))
+         {
+            if (dp->options & LIST_COMBOS)
+            {
+               int trx = tr;
+
+               fprintf(stderr, "(");
+               if (trx)
+               {
+                  int start = 0;
+
+                  while (trx)
+                  {
+                     int trz = trx & -trx;
+
+                     if (start) fprintf(stderr, "+");
+                     fprintf(stderr, "%s", transform_name(trz));
+                     start = 1;
+                     trx &= ~trz;
+                  }
+               }
+
+               else
+                  fprintf(stderr, "-");
+               fprintf(stderr, ")");
+            }
+
+            else
+               fprintf(stderr, "(0x%x)", tr);
+         }
+
+         else
+            fprintf(stderr, "(%s)", transform_name(tr));
+      }
+
+      fprintf(stderr, ": ");
+
+      va_start(ap, fmt);
+      vfprintf(stderr, fmt, ap);
+      va_end(ap);
+
+      fputc('\n', stderr);
+   }
+   /* else do not output any message */
+
+   /* Errors cause this routine to exit to the fail code */
+   if (level > APP_FAIL || (level > ERRORS && !(dp->options & CONTINUE)))
+      longjmp(dp->error_return, level);
+}
+
+/* error handler callbacks for libpng */
+static void PNGCBAPI
+display_warning(png_structp pp, png_const_charp warning)
+{
+   display_log(get_dp(pp), LIBPNG_WARNING, "%s", warning);
+}
+
+static void PNGCBAPI
+display_error(png_structp pp, png_const_charp error)
+{
+   struct display *dp = get_dp(pp);
+
+   display_log(dp, LIBPNG_ERROR, "%s", error);
+}
+
+static void
+display_cache_file(struct display *dp, const char *filename)
+   /* Does the initial cache of the file. */
+{
+   FILE *fp;
+   int ret;
+
+   dp->filename = filename;
+
+   if (filename != NULL)
+   {
+      fp = fopen(filename, "rb");
+      if (fp == NULL)
+         display_log(dp, USER_ERROR, "open failed: %s", strerror(errno));
+   }
+
+   else
+      fp = stdin;
+
+   ret = buffer_from_file(&dp->original_file, fp);
+
+   fclose(fp);
+
+   if (ret != 0)
+      display_log(dp, APP_ERROR, "read failed: %s", strerror(ret));
+}
+
+static void
+buffer_read(struct display *dp, struct buffer *bp, png_bytep data,
+   png_size_t size)
+{
+   struct buffer_list *last = bp->current;
+   size_t read_count = bp->read_count;
+
+   while (size > 0)
+   {
+      size_t avail;
+
+      if (last == NULL ||
+         (last == bp->last && read_count >= bp->end_count))
+      {
+         display_log(dp, USER_ERROR, "file truncated (%lu bytes)",
+            (unsigned long)size);
+         /*NOTREACHED*/
+         break;
+      }
+
+      else if (read_count >= sizeof last->buffer)
+      {
+         /* Move to the next buffer: */
+         last = last->next;
+         read_count = 0;
+         bp->current = last; /* Avoid update outside the loop */
+
+         /* And do a sanity check (the EOF case is caught above) */
+         if (last == NULL)
+         {
+            display_log(dp, INTERNAL_ERROR, "damaged buffer list");
+            /*NOTREACHED*/
+            break;
+         }
+      }
+
+      avail = (sizeof last->buffer) - read_count;
+      if (avail > size)
+         avail = size;
+
+      memcpy(data, last->buffer + read_count, avail);
+      read_count += avail;
+      size -= avail;
+      data += avail;
+   }
+
+   bp->read_count = read_count;
+}
+
+static void PNGCBAPI
+read_function(png_structp pp, png_bytep data, png_size_t size)
+{
+   buffer_read(get_dp(pp), get_buffer(pp), data, size);
+}
+
+static void
+read_png(struct display *dp, struct buffer *bp, const char *operation,
+   int transforms)
+{
+   png_structp pp;
+   png_infop   ip;
+
+   /* This cleans out any previous read and sets operation and transforms to
+    * empty.
+    */
+   display_clean_read(dp);
+
+   if (operation != NULL) /* else this is a verify and do not overwrite info */
+   {
+      dp->operation = operation;
+      dp->transforms = transforms;
+   }
+
+   dp->read_pp = pp = png_create_read_struct(PNG_LIBPNG_VER_STRING, dp,
+      display_error, display_warning);
+   if (pp == NULL)
+      display_log(dp, LIBPNG_ERROR, "failed to create read struct");
+
+   /* The png_read_png API requires us to make the info struct, but it does the
+    * call to png_read_info.
+    */
+   dp->read_ip = ip = png_create_info_struct(pp);
+   if (ip == NULL)
+      display_log(dp, LIBPNG_ERROR, "failed to create info struct");
+
+#  ifdef PNG_SET_USER_LIMITS_SUPPORTED
+      /* Remove the user limits, if any */
+      png_set_user_limits(pp, 0x7fffffff, 0x7fffffff);
+#  endif
+
+   /* Set the IO handling */
+   buffer_start_read(bp);
+   png_set_read_fn(pp, bp, read_function);
+
+   png_read_png(pp, ip, transforms, NULL/*params*/);
+
+#if 0 /* crazy debugging */
+   {
+      png_bytep pr = png_get_rows(pp, ip)[0];
+      size_t rb = png_get_rowbytes(pp, ip);
+      size_t cb;
+      char c = ' ';
+
+      fprintf(stderr, "%.4x %2d (%3lu bytes):", transforms, png_get_bit_depth(pp,ip), (unsigned long)rb);
+
+      for (cb=0; cb<rb; ++cb)
+         fputc(c, stderr), fprintf(stderr, "%.2x", pr[cb]), c='.';
+
+      fputc('\n', stderr);
+   }
+#endif
+}
+
+static void
+update_display(struct display *dp)
+   /* called once after the first read to update all the info, original_pp and
+    * original_ip must have been filled in.
+    */
+{
+   png_structp pp;
+   png_infop   ip;
+
+   /* Now perform the initial read with a 0 tranform. */
+   read_png(dp, &dp->original_file, "original read", 0/*no transform*/);
+
+   /* Move the result to the 'original' fields */
+   dp->original_pp = pp = dp->read_pp, dp->read_pp = NULL;
+   dp->original_ip = ip = dp->read_ip, dp->read_ip = NULL;
+
+   dp->original_rowbytes = png_get_rowbytes(pp, ip);
+   if (dp->original_rowbytes == 0)
+      display_log(dp, LIBPNG_BUG, "png_get_rowbytes returned 0");
+
+   dp->chunks = png_get_valid(pp, ip, 0xffffffff);
+   if ((dp->chunks & PNG_INFO_IDAT) == 0) /* set by png_read_png */
+      display_log(dp, LIBPNG_BUG, "png_read_png did not set IDAT flag");
+
+   dp->original_rows = png_get_rows(pp, ip);
+   if (dp->original_rows == NULL)
+      display_log(dp, LIBPNG_BUG, "png_read_png did not create row buffers");
+
+   if (!png_get_IHDR(pp, ip,
+      &dp->width, &dp->height, &dp->bit_depth, &dp->color_type,
+      &dp->interlace_method, &dp->compression_method, &dp->filter_method))
+      display_log(dp, LIBPNG_BUG, "png_get_IHDR failed");
+
+   /* 'active' transforms are discovered based on the original image format;
+    * running one active transform can activate others.  At present the code
+    * does not attempt to determine the closure.
+    */
+   {
+      png_uint_32 chunks = dp->chunks;
+      int active = 0, inactive = 0;
+      int ct = dp->color_type;
+      int bd = dp->bit_depth;
+      unsigned int i;
+
+      for (i=0; i<TTABLE_SIZE; ++i) if (transform_info[i].name != NULL)
+      {
+         int transform = transform_info[i].transform;
+
+         if ((transform_info[i].valid_chunks == 0 ||
+               (transform_info[i].valid_chunks & chunks) != 0) &&
+            (transform_info[i].color_mask_required & ct) ==
+               transform_info[i].color_mask_required &&
+            (transform_info[i].color_mask_absent & ct) == 0 &&
+            (transform_info[i].bit_depths & bd) != 0 &&
+            (transform_info[i].when & TRANSFORM_R) != 0)
+            active |= transform;
+
+         else if ((transform_info[i].when & TRANSFORM_R) != 0)
+            inactive |= transform;
+      }
+
+      /* Some transforms appear multiple times in the table; the 'active' status
+       * is the logical OR of these and the inactive status must be adjusted to
+       * take this into account.
+       */
+      inactive &= ~active;
+
+      dp->active_transforms = active;
+      dp->ignored_transforms = inactive; /* excluding write-only transforms */
+   }
+}
+
+static int
+compare_read(struct display *dp, int applied_transforms)
+{
+   /* Compare the png_info from read_ip with original_info */
+   size_t rowbytes;
+   png_uint_32 width, height;
+   int bit_depth, color_type;
+   int interlace_method, compression_method, filter_method;
+   const char *e = NULL;
+
+   png_get_IHDR(dp->read_pp, dp->read_ip, &width, &height, &bit_depth,
+      &color_type, &interlace_method, &compression_method, &filter_method);
+
+#  define C(item) if (item != dp->item) \
+      display_log(dp, APP_WARNING, "IHDR " #item "(%lu) changed to %lu",\
+         (unsigned long)dp->item, (unsigned long)item), e = #item
+
+   /* The IHDR should be identical: */
+   C(width);
+   C(height);
+   C(bit_depth);
+   C(color_type);
+   C(interlace_method);
+   C(compression_method);
+   C(filter_method);
+
+   /* 'e' remains set to the name of the last thing changed: */
+   if (e)
+      display_log(dp, APP_ERROR, "IHDR changed (%s)", e);
+
+   /* All the chunks from the original PNG should be preserved in the output PNG
+    * because the PNG format has not been changed.
+    */
+   {
+      unsigned long chunks =
+         png_get_valid(dp->read_pp, dp->read_ip, 0xffffffff);
+
+      if (chunks != dp->chunks)
+         display_log(dp, APP_FAIL, "PNG chunks changed from 0x%lx to 0x%lx",
+            (unsigned long)dp->chunks, chunks);
+   }
+
+   /* rowbytes should be the same */
+   rowbytes = png_get_rowbytes(dp->read_pp, dp->read_ip);
+
+   /* NOTE: on 64-bit systems this may trash the top bits of rowbytes,
+    * which could lead to weird error messages.
+    */
+   if (rowbytes != dp->original_rowbytes)
+      display_log(dp, APP_ERROR, "PNG rowbytes changed from %lu to %lu",
+         (unsigned long)dp->original_rowbytes, (unsigned long)rowbytes);
+
+   /* The rows should be the same too, unless the applied transforms includes
+    * the shift transform, in which case low bits may have been lost.
+    */
+   {
+      png_bytepp rows = png_get_rows(dp->read_pp, dp->read_ip);
+      unsigned int mask;  /* mask (if not zero) for the final byte */
+
+      if (bit_depth < 8)
+      {
+         /* Need the stray bits at the end, this depends only on the low bits
+          * of the image width; overflow does not matter.  If the width is an
+          * exact multiple of 8 bits this gives a mask of 0, not 0xff.
+          */
+         mask = 0xff & (0xff00 >> ((bit_depth * width) & 7));
+      }
+
+      else
+         mask = 0;
+
+      if (rows == NULL)
+         display_log(dp, LIBPNG_BUG, "png_get_rows returned NULL");
+
+      if ((applied_transforms & PNG_TRANSFORM_SHIFT) == 0 ||
+         (dp->active_transforms & PNG_TRANSFORM_SHIFT) == 0 ||
+         color_type == PNG_COLOR_TYPE_PALETTE)
+      {
+         unsigned long y;
+
+         for (y=0; y<height; ++y)
+         {
+            png_bytep row = rows[y];
+            png_bytep orig = dp->original_rows[y];
+
+            if (memcmp(row, orig, rowbytes-(mask != 0)) != 0 || (mask != 0 &&
+               ((row[rowbytes-1] & mask) != (orig[rowbytes-1] & mask))))
+            {
+               size_t x;
+
+               /* Find the first error */
+               for (x=0; x<rowbytes-1; ++x) if (row[x] != orig[x])
+                  break;
+
+               display_log(dp, APP_FAIL,
+                  "byte(%lu,%lu) changed 0x%.2x -> 0x%.2x",
+                  (unsigned long)x, (unsigned long)y, orig[x], row[x]);
+               return 0; /* don't keep reporting failed rows on 'continue' */
+            }
+         }
+      }
+
+      else
+      {
+         unsigned long y;
+         int bpp;   /* bits-per-pixel then bytes-per-pixel */
+         /* components are up to 8 bytes in size */
+         png_byte sig_bits[8];
+         png_color_8p sBIT;
+
+         if (png_get_sBIT(dp->read_pp, dp->read_ip, &sBIT) != PNG_INFO_sBIT)
+            display_log(dp, INTERNAL_ERROR,
+               "active shift transform but no sBIT in file");
+
+         switch (color_type)
+         {
+            case PNG_COLOR_TYPE_GRAY:
+               sig_bits[0] = sBIT->gray;
+               bpp = bit_depth;
+               break;
+
+            case PNG_COLOR_TYPE_GA:
+               sig_bits[0] = sBIT->gray;
+               sig_bits[1] = sBIT->alpha;
+               bpp = 2 * bit_depth;
+               break;
+
+            case PNG_COLOR_TYPE_RGB:
+               sig_bits[0] = sBIT->red;
+               sig_bits[1] = sBIT->green;
+               sig_bits[2] = sBIT->blue;
+               bpp = 3 * bit_depth;
+               break;
+
+            case PNG_COLOR_TYPE_RGBA:
+               sig_bits[0] = sBIT->red;
+               sig_bits[1] = sBIT->green;
+               sig_bits[2] = sBIT->blue;
+               sig_bits[3] = sBIT->alpha;
+               bpp = 4 * bit_depth;
+               break;
+
+            default:
+               display_log(dp, LIBPNG_ERROR, "invalid colour type %d",
+                  color_type);
+               /*NOTREACHED*/
+               bpp = 0;
+               break;
+         }
+
+         {
+            int b;
+
+            for (b=0; 8*b<bpp; ++b)
+            {
+               /* libpng should catch this; if not there is a security issue
+                * because an app (like this one) may overflow an array. In fact
+                * libpng doesn't catch this at present.
+                */
+               if (sig_bits[b] == 0 || sig_bits[b] > bit_depth/*!palette*/)
+                  display_log(dp, LIBPNG_BUG,
+                     "invalid sBIT[%u]  value %d returned for PNG bit depth %d",
+                     b, sig_bits[b], bit_depth);
+            }
+         }
+
+         if (bpp < 8 && bpp != bit_depth)
+         {
+            /* sanity check; this is a grayscale PNG; something is wrong in the
+             * code above.
+             */
+            display_log(dp, INTERNAL_ERROR, "invalid bpp %u for bit_depth %u",
+               bpp, bit_depth);
+         }
+
+         switch (bit_depth)
+         {
+            int b;
+
+            case 16: /* Two bytes per component, big-endian */
+               for (b = (bpp >> 4); b > 0; --b)
+               {
+                  unsigned int sig = (unsigned int)(0xffff0000 >> sig_bits[b]);
+
+                  sig_bits[2*b+1] = (png_byte)sig;
+                  sig_bits[2*b+0] = (png_byte)(sig >> 8); /* big-endian */
+               }
+               break;
+
+            case 8: /* One byte per component */
+               for (b=0; b*8 < bpp; ++b)
+                  sig_bits[b] = (png_byte)(0xff00 >> sig_bits[b]);
+               break;
+
+            case 1: /* allowed, but dumb */
+               /* Value is 1 */
+               sig_bits[0] = 0xff;
+               break;
+
+            case 2: /* Replicate 4 times */
+               /* Value is 1 or 2 */
+               b = 0x3 & ((0x3<<2) >> sig_bits[0]);
+               b |= b << 2;
+               b |= b << 4;
+               sig_bits[0] = (png_byte)b;
+               break;
+
+            case 4: /* Relicate twice */
+               /* Value is 1, 2, 3 or 4 */
+               b = 0xf & ((0xf << 4) >> sig_bits[0]);
+               b |= b << 4;
+               sig_bits[0] = (png_byte)b;
+               break;
+
+            default:
+               display_log(dp, LIBPNG_BUG, "invalid bit depth %d", bit_depth);
+               break;
+         }
+
+         /* Convert bpp to bytes; this gives '1' for low-bit depth grayscale,
+          * where there are multiple pixels per byte.
+          */
+         bpp = (bpp+7) >> 3;
+
+         /* The mask can be combined with sig_bits[0] */
+         if (mask != 0)
+         {
+            mask &= sig_bits[0];
+
+            if (bpp != 1 || mask == 0)
+               display_log(dp, INTERNAL_ERROR, "mask calculation error %u, %u",
+                  bpp, mask);
+         }
+
+         for (y=0; y<height; ++y)
+         {
+            png_bytep row = rows[y];
+            png_bytep orig = dp->original_rows[y];
+            unsigned long x;
+
+            for (x=0; x<(width-(mask!=0)); ++x)
+            {
+               int b;
+
+               for (b=0; b<bpp; ++b)
+               {
+                  if ((*row++ & sig_bits[b]) != (*orig++ & sig_bits[b]))
+                  {
+                     display_log(dp, APP_FAIL,
+                        "significant bits at (%lu[%u],%lu) changed %.2x->%.2x",
+                        x, b, y, orig[-1], row[-1]);
+                     return 0;
+                  }
+               }
+            }
+
+            if (mask != 0 && (*row & mask) != (*orig & mask))
+            {
+               display_log(dp, APP_FAIL,
+                  "significant bits at (%lu[end],%lu) changed", x, y);
+               return 0;
+            }
+         } /* for y */
+      }
+   }
+
+   return 1; /* compare succeeded */
+}
+
+#ifdef PNG_WRITE_SUPPORTED
+static void
+buffer_write(struct display *dp, struct buffer *buffer, png_bytep data,
+   png_size_t size)
+   /* Generic write function used both from the write callback provided to
+    * libpng and from the generic read code.
+    */
+{
+   /* Write the data into the buffer, adding buffers as required */
+   struct buffer_list *last = buffer->last;
+   size_t end_count = buffer->end_count;
+
+   while (size > 0)
+   {
+      size_t avail;
+
+      if (end_count >= sizeof last->buffer)
+      {
+         if (last->next == NULL)
+         {
+            last = buffer_extend(last);
+
+            if (last == NULL)
+               display_log(dp, APP_ERROR, "out of memory saving file");
+         }
+
+         else
+            last = last->next;
+
+         buffer->last = last; /* avoid the need to rewrite every time */
+         end_count = 0;
+      }
+
+      avail = (sizeof last->buffer) - end_count;
+      if (avail > size)
+         avail = size;
+
+      memcpy(last->buffer + end_count, data, avail);
+      end_count += avail;
+      size -= avail;
+      data += avail;
+   }
+
+   buffer->end_count = end_count;
+}
+
+static void PNGCBAPI
+write_function(png_structp pp, png_bytep data, png_size_t size)
+{
+   buffer_write(get_dp(pp), get_buffer(pp), data, size);
+}
+
+static void
+write_png(struct display *dp, png_infop ip, int transforms)
+{
+   display_clean_write(dp); /* safety */
+
+   buffer_start_write(&dp->written_file);
+   dp->operation = "write";
+   dp->transforms = transforms;
+
+   dp->write_pp = png_create_write_struct(PNG_LIBPNG_VER_STRING, dp,
+      display_error, display_warning);
+
+   if (dp->write_pp == NULL)
+      display_log(dp, APP_ERROR, "failed to create write png_struct");
+
+   png_set_write_fn(dp->write_pp, &dp->written_file, write_function,
+      NULL/*flush*/);
+
+#  ifdef PNG_SET_USER_LIMITS_SUPPORTED
+      /* Remove the user limits, if any */
+      png_set_user_limits(dp->write_pp, 0x7fffffff, 0x7fffffff);
+#  endif
+
+   /* Certain transforms require the png_info to be zapped to allow the
+    * transform to work correctly.
+    */
+   if (transforms & (PNG_TRANSFORM_PACKING|
+                     PNG_TRANSFORM_STRIP_FILLER|
+                     PNG_TRANSFORM_STRIP_FILLER_BEFORE))
+   {
+      int ct = dp->color_type;
+
+      if (transforms & (PNG_TRANSFORM_STRIP_FILLER|
+                        PNG_TRANSFORM_STRIP_FILLER_BEFORE))
+         ct &= ~PNG_COLOR_MASK_ALPHA;
+
+      png_set_IHDR(dp->write_pp, ip, dp->width, dp->height, dp->bit_depth, ct,
+         dp->interlace_method, dp->compression_method, dp->filter_method);
+   }
+
+   png_write_png(dp->write_pp, ip, transforms, NULL/*params*/);
+
+   /* Clean it on the way out - if control returns to the caller then the
+    * written_file contains the required data.
+    */
+   display_clean_write(dp);
+}
+#endif /* WRITE_SUPPORTED */
+
+static int
+skip_transform(struct display *dp, int tr)
+   /* Helper to test for a bad combo and log it if it is skipped */
+{
+   if ((dp->options & SKIP_BUGS) != 0 && is_bad_combo(tr))
+   {
+      /* Log this to stdout if logging is on, otherwise just do an information
+       * display_log.
+       */
+      if ((dp->options & LOG_SKIPPED) != 0)
+      {
+         printf("SKIP: %s transforms ", dp->filename);
+
+         while (tr != 0)
+         {
+            int next = first_transform(tr);
+            tr &= ~next;
+
+            printf("%s", transform_name(next));
+            if (tr != 0)
+               putchar('+');
+         }
+
+         putchar('\n');
+      }
+
+      else
+         display_log(dp, INFORMATION, "%s: skipped known bad combo 0x%x",
+            dp->filename, tr);
+
+      return 1; /* skip */
+   }
+
+   return 0; /* don't skip */
+}
+
+static void
+test_one_file(struct display *dp, const char *filename)
+{
+   /* First cache the file and update the display original file
+    * information for the new file.
+    */
+   dp->operation = "cache file";
+   dp->transforms = 0;
+   display_cache_file(dp, filename);
+   update_display(dp);
+
+   /* First test: if there are options that should be ignored for this file
+    * verify that they really are ignored.
+    */
+   if (dp->ignored_transforms != 0)
+   {
+      read_png(dp, &dp->original_file, "ignored transforms",
+         dp->ignored_transforms);
+
+      /* The result should be identical to the original_rows */
+      if (!compare_read(dp, 0/*transforms applied*/))
+         return; /* no point testing more */
+   }
+
+#ifdef PNG_WRITE_SUPPORTED
+   /* Second test: write the original PNG data out to a new file (to test the
+    * write side) then read the result back in and make sure that it hasn't
+    * changed.
+    */
+   dp->operation = "write";
+   write_png(dp, dp->original_ip, 0/*transforms*/);
+   read_png(dp, &dp->written_file, NULL, 0/*transforms*/);
+   if (!compare_read(dp, 0/*transforms applied*/))
+      return;
+#endif
+
+   /* Third test: the active options.  Test each in turn, or, with the
+    * EXHAUSTIVE option, test all possible combinations.
+    */
+   {
+      /* Use unsigned int here because the code below to increment through all
+       * the possibilities exhaustively has to use a compare and that must be
+       * unsigned, because some transforms are negative on a 16-bit system.
+       */
+      unsigned int active = dp->active_transforms;
+      const int exhaustive = (dp->options & EXHAUSTIVE) != 0;
+      unsigned int current = first_transform(active);
+      unsigned int bad_transforms = 0;
+      unsigned int bad_combo = ~0U;    /* bitwise AND of failing transforms */
+      unsigned int bad_combo_list = 0; /* bitwise OR of failures */
+
+      for (;;)
+      {
+         read_png(dp, &dp->original_file, "active transforms", current);
+
+         /* If this involved any irreversible transformations then if we write
+          * it out with just the reversible transformations and read it in again
+          * with the same transforms we should get the same thing.  At present
+          * this isn't done - it just seems like a waste of time and it would
+          * require two sets of read png_struct/png_info.
+          *
+          * If there were no irreversible transformations then if we write it
+          * out and read it back in again (without the reversible transforms)
+          * we should get back to the place where we started.
+          */
+#ifdef PNG_WRITE_SUPPORTED
+         if ((current & write_transforms) == current)
+         {
+            /* All transforms reversible: write the PNG with the transformations
+             * reversed, then read it back in with no transformations.  The
+             * result should be the same as the original apart from the loss of
+             * low order bits because of the SHIFT/sBIT transform.
+             */
+            dp->operation = "reversible transforms";
+            write_png(dp, dp->read_ip, current);
+
+            /* And if this is read back in, because all the transformations were
+             * reversible, the result should be the same.
+             */
+            read_png(dp, &dp->written_file, NULL, 0);
+            if (!compare_read(dp, current/*for the SHIFT/sBIT transform*/))
+            {
+               /* This set of transforms failed.  If a single bit is set - if
+                * there is just one transform - don't include this in further
+                * 'exhaustive' tests.  Notice that each transform is tested on
+                * its own before testing combos in the exhaustive case.
+                */
+               if (is_combo(current))
+               {
+                  bad_combo &= current;
+                  bad_combo_list |= current;
+               }
+
+               else
+                  bad_transforms |= current;
+            }
+         }
+#endif
+
+         /* Now move to the next transform */
+         if (exhaustive) /* all combinations */
+         {
+            unsigned int next = current;
+
+            do
+            {
+               if (next == read_transforms) /* Everything tested */
+                  goto combo;
+
+               ++next;
+            }  /* skip known bad combos if the relevant option is set; skip
+                * combos involving known bad single transforms in all cases.
+                */
+            while (  (next & read_transforms) <= current
+                  || (next & active) == 0 /* skip cases that do nothing */
+                  || (next & bad_transforms) != 0
+                  || skip_transform(dp, next));
+
+            assert((next & read_transforms) == next);
+            current = next;
+         }
+
+         else /* one at a time */
+         {
+            active &= ~current;
+
+            if (active == 0)
+               goto combo;
+
+            current = first_transform(active);
+         }
+      }
+
+combo:
+      if (dp->options & FIND_BAD_COMBOS)
+      {
+         /* bad_combos identifies the combos that occur in all failing cases;
+          * bad_combo_list identifies transforms that do not prevent the
+          * failure.
+          */
+         if (bad_combo != ~0U)
+            printf("%s[0x%x]: PROBLEM: 0x%x[0x%x] ANTIDOTE: 0x%x\n",
+               dp->filename, active, bad_combo, bad_combo_list,
+               rw_transforms & ~bad_combo_list);
+
+         else
+            printf("%s: no %sbad combos found\n", dp->filename,
+               (dp->options & SKIP_BUGS) ? "additional " : "");
+      }
+   }
+}
+
+static int
+do_test(struct display *dp, const char *file)
+   /* Exists solely to isolate the setjmp clobbers */
+{
+   int ret = setjmp(dp->error_return);
+
+   if (ret == 0)
+   {
+      test_one_file(dp, file);
+      return 0;
+   }
+
+   else if (ret < ERRORS) /* shouldn't longjmp on warnings */
+      display_log(dp, INTERNAL_ERROR, "unexpected return code %d", ret);
+
+   return ret;
+}
+
+int
+main(const int argc, const char * const * const argv)
+{
+   /* For each file on the command line test it with a range of transforms */
+   int option_end, ilog = 0;
+   struct display d;
+
+   validate_T();
+   display_init(&d);
+
+   for (option_end=1; option_end<argc; ++option_end)
+   {
+      const char *name = argv[option_end];
+
+      if (strcmp(name, "--verbose") == 0)
+         d.options = (d.options & ~LEVEL_MASK) | VERBOSE;
+
+      else if (strcmp(name, "--warnings") == 0)
+         d.options = (d.options & ~LEVEL_MASK) | WARNINGS;
+
+      else if (strcmp(name, "--errors") == 0)
+         d.options = (d.options & ~LEVEL_MASK) | ERRORS;
+
+      else if (strcmp(name, "--quiet") == 0)
+         d.options = (d.options & ~LEVEL_MASK) | QUIET;
+
+      else if (strcmp(name, "--exhaustive") == 0)
+         d.options |= EXHAUSTIVE;
+
+      else if (strcmp(name, "--fast") == 0)
+         d.options &= ~EXHAUSTIVE;
+
+      else if (strcmp(name, "--strict") == 0)
+         d.options |= STRICT;
+
+      else if (strcmp(name, "--relaxed") == 0)
+         d.options &= ~STRICT;
+
+      else if (strcmp(name, "--log") == 0)
+      {
+         ilog = option_end; /* prevent display */
+         d.options |= LOG;
+      }
+
+      else if (strcmp(name, "--nolog") == 0)
+         d.options &= ~LOG;
+
+      else if (strcmp(name, "--continue") == 0)
+         d.options |= CONTINUE;
+
+      else if (strcmp(name, "--stop") == 0)
+         d.options &= ~CONTINUE;
+
+      else if (strcmp(name, "--skip-bugs") == 0)
+         d.options |= SKIP_BUGS;
+
+      else if (strcmp(name, "--test-all") == 0)
+         d.options &= ~SKIP_BUGS;
+
+      else if (strcmp(name, "--log-skipped") == 0)
+         d.options |= LOG_SKIPPED;
+
+      else if (strcmp(name, "--nolog-skipped") == 0)
+         d.options &= ~LOG_SKIPPED;
+
+      else if (strcmp(name, "--find-bad-combos") == 0)
+         d.options |= FIND_BAD_COMBOS;
+
+      else if (strcmp(name, "--nofind-bad-combos") == 0)
+         d.options &= ~FIND_BAD_COMBOS;
+
+      else if (strcmp(name, "--list-combos") == 0)
+         d.options |= LIST_COMBOS;
+
+      else if (strcmp(name, "--nolist-combos") == 0)
+         d.options &= ~LIST_COMBOS;
+
+      else if (name[0] == '-' && name[1] == '-')
+      {
+         fprintf(stderr, "pngimage: %s: unknown option\n", name);
+         return 99;
+      }
+
+      else
+         break; /* Not an option */
+   }
+
+   {
+      int i;
+      int errors = 0;
+
+      for (i=option_end; i<argc; ++i)
+      {
+         {
+            int ret = do_test(&d, argv[i]);
+
+            if (ret > QUIET) /* abort on user or internal error */
+               return 99;
+         }
+
+         /* Here on any return, including failures, except user/internal issues
+          */
+         {
+            const int pass = (d.options & STRICT) ?
+               RESULT_STRICT(d.results) : RESULT_RELAXED(d.results);
+
+            if (!pass)
+               ++errors;
+
+            if (d.options & LOG)
+            {
+               int j;
+
+               printf("%s: pngimage ", pass ? "PASS" : "FAIL");
+
+               for (j=1; j<option_end; ++j) if (j != ilog)
+                  printf("%s ", argv[j]);
+
+               printf("%s\n", d.filename);
+            }
+         }
+
+         display_clean(&d);
+      }
+
+      /* Release allocated memory */
+      display_destroy(&d);
+
+      return errors != 0;
+   }
+}
+#else /* !INFO_IMAGE || !SEQUENTIAL_READ || !READ_PNG*/
+int
+main(void)
+{
+   fprintf(stderr, "pngimage: no support for png_read/write_image\n");
+   return SKIP;
+}
+#endif