pngcp: tool to copy PNG files

This adds pngcp to the build together with a pngcp.dfa configuration test; the
test revealed some configuration bugs which are fixed by corrections to the
_SUPPORTED macros.

pngcp builds on all tested configurations and a number of bugs have been fixed
to make this happen relative to the version in libpng 1.7 contrib/examples.
pngcp.dfa will have to be different for 1.7 but pngcp.c should work fine (not
yet tested).  pngcp itself is still missing a usage message; this is a
preliminary version, although since it behaves the same way as 'cp' most unoids
shouldn't have a problem using it correctly.

Signed-off-by: John Bowler <jbowler@acm.org>

7 files changed, 2344 insertions, 3 deletions

diff --git a/Makefile.am b/Makefile.am
index 721295184..39e9bdeed 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -18,7 +18,7 @@ check_PROGRAMS += timepng
 endif
 
 # Utilities - installed
-bin_PROGRAMS= pngfix png-fix-itxt
+bin_PROGRAMS= pngcp pngfix png-fix-itxt
 
 # This ensures that pnglibconf.h gets built at the start of 'make all' or
 # 'make check', but it does not add dependencies to the individual programs,
@@ -53,6 +53,9 @@ pngfix_LDADD = libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@.la
 
 png_fix_itxt_SOURCES = contrib/tools/png-fix-itxt.c
 
+pngcp_SOURCES = contrib/tools/pngcp.c
+pngcp_LDADD = libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@.la
+
 # Generally these are single line shell scripts to run a test with a particular
 # set of parameters:
 TESTS =\
@@ -230,6 +233,7 @@ contrib/libtests/timepng.o: pnglibconf.h
 
 contrib/tools/makesRGB.o: pnglibconf.h
 contrib/tools/pngfix.o: pnglibconf.h
+contrib/tools/pngcp.o: pnglibconf.h
 
 # We must use -DPNG_NO_USE_READ_MACROS here even when the library may actually
 # be built with PNG_USE_READ_MACROS; this prevents the read macros from
diff --git a/contrib/conftest/pngcp.dfa b/contrib/conftest/pngcp.dfa
new file mode 100644
index 000000000..2b4b66926
--- /dev/null
+++ b/contrib/conftest/pngcp.dfa
@@ -0,0 +1,46 @@
+# pngcp.dfa
+#  Build time configuration of libpng
+#
+# Author: John Bowler
+# Copyright: (c) John Bowler, 2016
+# Usage rights:
+#  To the extent possible under law, the author has waived all copyright and
+#  related or neighboring rights to this work.  This work is published from:
+#  United States.
+#
+# Build libpng with support for pngcp.  This means just png_read_png,
+# png_write_png and small number of configuration settings.
+#
+everything = off
+
+# Options to turn on png_read_png and png_write_png:
+option INFO_IMAGE on
+option SEQUENTIAL_READ on
+option EASY_ACCESS on
+option WRITE on
+option WRITE_16BIT on
+option WRITE_FILTER on
+
+# pngcp needs this to preserve unknown chunks, switching all these on means that
+# pngcp can work without explicit known chunk reading suppport
+option UNKNOWN_CHUNKS on
+option SET_UNKNOWN_CHUNKS on
+option HANDLE_AS_UNKNOWN on
+option SAVE_UNKNOWN_CHUNKS on
+option WRITE_UNKNOWN_CHUNKS on
+
+# pngcp needs this to handle palette files with invalid indices:
+option CHECK_FOR_INVALID_INDEX on
+option GET_PALETTE_MAX on
+
+# Pre-libpng 1.7 pngcp has to stash text chunks manually, post 1.7 without this
+# text chunks should be handled as unknown ok.
+option TEXT on
+
+# this is used to turn off limits:
+option USER_LIMITS on
+option SET_USER_LIMITS on
+
+# these are are just required for specific customizations
+option WRITE_CUSTOMIZE_ZTXT_COMPRESSION on
+option WRITE_CUSTOMIZE_COMPRESSION on
diff --git a/contrib/libtests/pngimage.c b/contrib/libtests/pngimage.c
index 2ebe553f6..4f6946427 100644
--- a/contrib/libtests/pngimage.c
+++ b/contrib/libtests/pngimage.c
@@ -1082,6 +1082,7 @@ compare_read(struct display *dp, int applied_transforms)
       }
 
       else
+#     ifdef PNG_sBIT_SUPPORTED
       {
          unsigned long y;
          int bpp;   /* bits-per-pixel then bytes-per-pixel */
@@ -1243,6 +1244,10 @@ compare_read(struct display *dp, int applied_transforms)
             }
          } /* for y */
       }
+#     else /* !sBIT */
+         display_log(dp, INTERNAL_ERROR,
+               "active shift transform but no sBIT support");
+#     endif /* !sBIT */
    }
 
    return 1; /* compare succeeded */
diff --git a/contrib/tools/pngcp.c b/contrib/tools/pngcp.c
new file mode 100644
index 000000000..660acfc7b
--- /dev/null
+++ b/contrib/tools/pngcp.c
@@ -0,0 +1,2279 @@
+/* pngcp.c
+ *
+ * Copyright (c) 2016 John Cunningham Bowler
+ *
+ * Last changed in libpng 1.6.24beta03 [June 27, 2016]
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ *
+ * This is an example of copying a PNG without changes using the png_read_png
+ * and png_write_png interfaces.  A considerable number of options are provided
+ * to manipulate the compression of the PNG data and other compressed chunks.
+ *
+ * For a more extensive example that uses the transforms see
+ * contrib/libtests/pngimage.c in the libpng distribution.
+ */
+#define _POSIX_SOURCE 1
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <stdio.h>
+#include <limits.h>
+#include <assert.h>
+
+#include <unistd.h>
+#include <sys/stat.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
+
+#include <zlib.h>
+
+#ifndef PNG_SETJMP_SUPPORTED
+#  include <setjmp.h> /* because png.h did *not* include this */
+#endif
+
+#ifdef __cplusplus
+#  define voidcast(type, value) static_cast<type>(value)
+#else
+#  define voidcast(type, value) (value)
+#endif /* __cplusplus */
+
+#ifdef __GNUC__
+   /* Many versions of GCC erroneously report that local variables unmodified
+    * within the scope of a setjmp may be clobbered.  This hacks round the
+    * problem (sometimes) without harming other compilers.
+    */
+#  define gv volatile
+#else
+#  define gv
+#endif
+
+#if PNG_LIBPNG_VER < 10700
+   /* READ_PNG and WRITE_PNG were not defined, so: */
+#  ifdef PNG_INFO_IMAGE_SUPPORTED
+#     ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+#        define PNG_READ_PNG_SUPPORTED
+#     endif /* SEQUENTIAL_READ */
+#     ifdef PNG_WRITE_SUPPORTED
+#        define PNG_WRITE_PNG_SUPPORTED
+#     endif /* WRITE */
+#  endif /* INFO_IMAGE */
+#endif /* pre 1.7.0 */
+
+#if (defined(PNG_READ_PNG_SUPPORTED)) && (defined(PNG_WRITE_PNG_SUPPORTED))
+/* 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 STRICT          0x010 /* Fail on warnings as well as errors */
+#define LOG             0x020 /* Log pass/fail to stdout */
+#define CONTINUE        0x040 /* Continue on APP_FAIL errors */
+#define SIZES           0x080 /* Report input and output sizes */
+#define SEARCH          0x100 /* Search IDAT compression options */
+#define NOWRITE         0x200 /* Do not write an output file */
+#ifdef PNG_CHECK_FOR_INVALID_INDEX_SUPPORTED
+#  define IGNORE_INDEX  0x400 /* Ignore out of range palette indices (BAD!) */
+#  ifdef PNG_GET_PALETTE_MAX_SUPPORTED
+#     define FIX_INDEX  0x800 /* 'Fix' out of range palette indices (OK) */
+#  endif /* GET_PALETTE_MAX */
+#endif /* CHECK_FOR_INVALID_INDEX */
+#define OPTION     0x80000000 /* Used for handling options */
+#define LIST       0x80000001 /* Used for handling options */
+
+/* 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)
+
+/* OPTION DEFINITIONS */
+static const char range_lo[] = "low";
+static const char range_hi[] = "high";
+static const char all[] = "all";
+#define RANGE(lo,hi) { range_lo, lo }, { range_hi, hi }
+typedef struct value_list
+{
+   const char *name;  /* the command line name of the value */
+   int         value; /* the actual value to use */
+}  value_list;
+
+static const value_list
+#ifdef PNG_SW_COMPRESS_png_level
+vl_compression[] =
+{
+   /* Overall compression control.  The order controls the search order for
+    * 'all'.  Since the search is for the smallest the order used is low memory
+    * then high speed.
+    */
+   { "low-memory",      PNG_COMPRESSION_LOW_MEMORY },
+   { "high-speed",      PNG_COMPRESSION_HIGH_SPEED },
+   { "high-read-speed", PNG_COMPRESSION_HIGH_READ_SPEED },
+   { "low",             PNG_COMPRESSION_LOW },
+   { "medium",          PNG_COMPRESSION_MEDIUM },
+   { "old",             PNG_COMPRESSION_COMPAT },
+   { "high",            PNG_COMPRESSION_HIGH },
+   { all, 0 }
+},
+#endif /* SW_COMPRESS_png_level */
+
+#if defined(PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED) ||\
+    defined(PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED)
+vl_strategy[] =
+{
+   /* This controls the order of search. */
+   { "huffman", Z_HUFFMAN_ONLY },
+   { "RLE", Z_RLE },
+   { "fixed", Z_FIXED }, /* the remainder do window searchs */
+   { "filtered", Z_FILTERED },
+   { "default", Z_DEFAULT_STRATEGY },
+   { all, 0 }
+},
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
+vl_windowBits_text[] =
+{
+   { "default", MAX_WBITS/*from zlib*/ },
+   { "minimum", 8 },
+   RANGE(8, MAX_WBITS/*from zlib*/),
+   { all, 0 }
+},
+#endif /* text compression */
+vl_level[] =
+{
+   { "default", Z_DEFAULT_COMPRESSION /* this is -1 */ },
+   { "none", Z_NO_COMPRESSION },
+   { "speed", Z_BEST_SPEED },
+   { "best", Z_BEST_COMPRESSION },
+   { "0", Z_NO_COMPRESSION },
+   RANGE(1, 9), /* this deliberately excludes '0' */
+   { all, 0 }
+},
+vl_memLevel[] =
+{
+   { "max", MAX_MEM_LEVEL }, /* zlib maximum */
+   { "1", 1 }, /* zlib minimum */
+   { "default", 8 }, /* zlib default */
+   { "2", 2 },
+   { "3", 3 },
+   { "4", 4 },
+   { "5", 5 }, /* for explicit testing */
+   RANGE(6, MAX_MEM_LEVEL/*zlib*/), /* exclude 5 and below: zlib bugs */
+   { all, 0 }
+},
+#endif /* WRITE_CUSTOMIZE_*COMPRESSION */
+#ifdef PNG_WRITE_FILTER_SUPPORTED
+vl_filter[] =
+{
+   { all,      PNG_ALL_FILTERS   },
+   { "off",    PNG_NO_FILTERS    },
+   { "none",   PNG_FILTER_NONE   },
+   { "sub",    PNG_FILTER_SUB    },
+   { "up",     PNG_FILTER_UP     },
+   { "avg",    PNG_FILTER_AVG    },
+   { "paeth",  PNG_FILTER_PAETH  }
+},
+#endif /* WRITE_FILTER */
+vl_IDAT_size[] = /* for png_set_IDAT_size */
+{
+   { "default", 0x7FFFFFFF },
+   { "minimal", 1 },
+   RANGE(1, 0x7FFFFFFF)
+},
+#ifndef PNG_SW_IDAT_size
+   /* Pre 1.7 API: */
+#  define png_set_IDAT_size(p,v) png_set_compression_buffer_size(p, v)
+#endif /* !SW_IDAT_size */
+#define SL 8 /* stack limit in display, below */
+vl_log_depth[] = { { "on", 1 }, { "off", 0 }, RANGE(0, SL) },
+vl_on_off[] = { { "on", 1 }, { "off", 0 } };
+
+#ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
+static value_list
+vl_windowBits_IDAT[] =
+{
+   { "default", MAX_WBITS },
+   { "small", 9 },
+   RANGE(8, MAX_WBITS), /* modified by set_windowBits_hi */
+   { all, 0 }
+};
+#endif /* IDAT compression */
+
+typedef struct option
+{
+   const char       *name;         /* name of the option */
+   png_uint_32       opt;          /* an option, or OPTION or LIST */
+   png_byte          search;       /* Search on --search */
+   png_byte          value_count;  /* length of the list of values: */
+   const value_list *values;       /* values for OPTION or LIST */
+}  option;
+
+static const option options[] =
+{
+   /* struct display options, these are set when the command line is read */
+#  define S(n,v) { #n, v, 0, 2, vl_on_off },
+   S(verbose,  VERBOSE)
+   S(warnings, WARNINGS)
+   S(errors,   ERRORS)
+   S(quiet,    QUIET)
+   S(strict,   STRICT)
+   S(log,      LOG)
+   S(continue, CONTINUE)
+   S(sizes,    SIZES)
+   S(search,   SEARCH)
+   S(nowrite,  NOWRITE)
+#  ifdef IGNORE_INDEX
+      S(ignore-palette-index, IGNORE_INDEX)
+#  endif /* IGNORE_INDEX */
+#  ifdef FIX_INDEX
+      S(fix-palette-index, FIX_INDEX)
+#  endif /* FIX_INDEX */
+#  undef S
+
+   /* OPTION settings, these and LIST settings are read on demand */
+#  define VLNAME(name) vl_ ## name
+#  define VLSIZE(name) voidcast(png_byte,\
+                           (sizeof VLNAME(name))/(sizeof VLNAME(name)[0]))
+#  define VL(oname, name, type, search)\
+   { oname, type, search, VLSIZE(name), VLNAME(name) },
+#  define VLO(oname, name, search) VL(oname, name, OPTION, search)
+
+#  ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
+#     define VLCIDAT(name) VLO(#name, name, 1/*search*/)
+#     ifdef PNG_SW_COMPRESS_level
+#        define VLCiCCP(name) VLO("ICC-profile-" #name, name, 0/*search*/)
+#     else
+#        define VLCiCCP(name)
+#     endif
+#  else
+#     define VLCIDAT(name)
+#     define VLCiCCP(name)
+#  endif /* WRITE_CUSTOMIZE_COMPRESSION */
+
+#  ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
+#     define VLCzTXt(name) VLO("text-" #name, name, 0/*search*/)
+#  else
+#     define VLCzTXt(name)
+#  endif /* WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+
+#  define VLC(name) VLCIDAT(name) VLCiCCP(name) VLCzTXt(name)
+
+#  ifdef PNG_SW_COMPRESS_png_level
+      /* The libpng compression level isn't searched beause it justs sets the
+       * other things that are searched!
+       */
+      VLO("compression", compression, 0)
+      VLO("text-compression", compression, 0)
+      VLO("ICC-profile-compression", compression, 0)
+#  endif /* SW_COMPRESS_png_level */
+   VLC(strategy)
+   VLO("windowBits", windowBits_IDAT, 1)
+#  ifdef PNG_SW_COMPRESS_windowBits
+      VLO("ICC-profile-windowBits", windowBits_text/*sic*/, 0)
+#  endif
+   VLO("text-windowBits", windowBits_text, 0)
+   VLC(level)
+   VLC(memLevel)
+   VLO("IDAT-size", IDAT_size, 0)
+   VLO("log-depth", log_depth, 0)
+
+#  undef VLO
+
+   /* LIST settings */
+#  define VLL(name, search) VL(#name, name, LIST, search)
+#ifdef PNG_WRITE_FILTER_SUPPORTED
+   VLL(filter, 0)
+#endif /* WRITE_FILTER */
+#  undef VLL
+#  undef VL
+};
+
+#ifdef __cplusplus
+   static const size_t option_count((sizeof options)/(sizeof options[0]));
+#else /* !__cplusplus */
+#  define option_count ((sizeof options)/(sizeof options[0]))
+#endif /* !__cplusplus */
+
+static const char *
+cts(int ct)
+{
+   switch (ct)
+   {
+      case PNG_COLOR_TYPE_PALETTE:     return "P";
+      case PNG_COLOR_TYPE_GRAY:        return "G";
+      case PNG_COLOR_TYPE_GRAY_ALPHA:  return "GA";
+      case PNG_COLOR_TYPE_RGB:         return "RGB";
+      case PNG_COLOR_TYPE_RGB_ALPHA:   return "RGBA";
+      default:                         return "INVALID";
+   }
+}
+
+struct display
+{
+   jmp_buf          error_return;      /* Where to go to on error */
+   unsigned int     errset;            /* error_return is set */
+
+   const char      *operation;         /* What is happening */
+   const char      *filename;          /* The name of the original file */
+   const char      *output_file;       /* The name of the output file */
+
+   /* Used on both read and write: */
+   FILE            *fp;
+
+   /* Used on a read, both the original read and when validating a written
+    * image.
+    */
+   png_alloc_size_t read_size;
+   png_structp      read_pp;
+   png_infop        ip;
+#  if PNG_LIBPNG_VER < 10700 && defined PNG_TEXT_SUPPORTED
+      png_textp     text_ptr; /* stash of text chunks */
+      int           num_text;
+      int           text_stashed;
+#  endif /* pre 1.7 */
+
+   /* Used to write a new image (the original info_ptr is used) */
+#  define MAX_SIZE ((png_alloc_size_t)(-1))
+   png_alloc_size_t write_size;
+   png_alloc_size_t best_size;
+   png_structp      write_pp;
+
+   /* Base file information */
+   png_alloc_size_t size;
+   png_uint_32      w;
+   png_uint_32      h;
+   int              bpp;
+   png_byte         ct;
+   int              no_warnings;       /* Do not output libpng warnings */
+   int              min_windowBits;    /* The windowBits range is 8..8 */
+
+   /* Options handling */
+   png_uint_32      results;             /* A mask of errors seen */
+   png_uint_32      options;             /* See display_log below */
+   png_byte         entry[option_count]; /* The selected entry+1 of an option
+                                          * that appears on the command line, or
+                                          * 0 if it was not given. */
+   int              value[option_count]; /* Corresponding value */
+
+   /* Compression exhaustive testing */
+   /* Temporary variables used only while testing a single collection of
+    * settings:
+    */
+   unsigned int     csp;               /* next stack entry to use */
+   unsigned int     nsp;               /* highest active entry+1 found so far */
+
+   /* Values used while iterating through all the combinations of settings for a
+    * single file:
+    */
+   unsigned int     tsp;               /* nsp from the last run; this is the
+                                        * index+1 of the highest active entry on
+                                        * this run; this entry will be advanced.
+                                        */
+   int              opt_string_start;  /* Position in buffer for the first
+                                        * searched option; non-zero if earlier
+                                        * options were set on the command line.
+                                        */
+   struct stack
+   {
+      png_alloc_size_t best_size;      /* Best so far for this option */
+      png_alloc_size_t lo_size;
+      png_alloc_size_t hi_size;
+      int              lo, hi;         /* For binary chop of a range */
+      int              best_val;       /* Best value found so far */
+      int              opt_string_end; /* End of the option string in 'curr' */
+      png_byte         opt;            /* The option being tested */
+      png_byte         entry;          /* The next value entry to be tested */
+      png_byte         end;            /* This is the last entry */
+   }                stack[SL];         /* Stack of entries being tested */
+   char             curr[32*SL];       /* current options being tested */
+   char             best[32*SL];       /* best options */
+
+   char             namebuf[FILENAME_MAX+1]; /* output file name */
+};
+
+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->operation = "internal error";
+   dp->filename = "command line";
+   dp->output_file = "no output file";
+   dp->options = WARNINGS; /* default to !verbose, !quiet */
+   dp->fp = NULL;
+   dp->read_pp = NULL;
+   dp->ip = NULL;
+   dp->write_pp = NULL;
+   dp->min_windowBits = -1; /* this is an OPTIND, so -1 won't match anything */
+#  if PNG_LIBPNG_VER < 10700 && defined PNG_TEXT_SUPPORTED
+      dp->text_ptr = NULL;
+      dp->num_text = 0;
+      dp->text_stashed = 0;
+#  endif /* pre 1.7 */
+}
+
+static void
+display_clean_read(struct display *dp)
+{
+   if (dp->read_pp != NULL)
+      png_destroy_read_struct(&dp->read_pp, NULL, NULL);
+
+   if (dp->fp != NULL)
+   {
+      FILE *fp = dp->fp;
+      dp->fp = NULL;
+      (void)fclose(fp);
+   }
+}
+
+static void
+display_clean_write(struct display *dp)
+{
+   if (dp->fp != NULL)
+   {
+      FILE *fp = dp->fp;
+      dp->fp = NULL;
+      (void)fclose(fp);
+   }
+
+   if (dp->write_pp != NULL)
+      png_destroy_write_struct(&dp->write_pp, dp->tsp > 0 ? NULL : &dp->ip);
+}
+
+static void
+display_clean(struct display *dp)
+{
+   display_clean_read(dp);
+   display_clean_write(dp);
+   dp->output_file = NULL;
+
+#  if PNG_LIBPNG_VER < 10700 && defined PNG_TEXT_SUPPORTED
+      /* This is actually created and used by the write code, but only
+       * once; it has to be retained for subsequent writes of the same file.
+       */
+      if (dp->text_stashed)
+      {
+         dp->text_stashed = 0;
+         dp->num_text = 0;
+         free(dp->text_ptr);
+         dp->text_ptr = NULL;
+      }
+#  endif /* pre 1.7 */
+
+   /* 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. */
+   display_clean(dp);
+}
+
+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, "pngcp: 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(pngcp)"; 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(pngcp)"; 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(pngcp)"; break;
+      }
+
+      fprintf(stderr, "%s: %s: %s",
+         dp->filename != NULL ? dp->filename : "<stdin>", lp, dp->operation);
+
+      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)))
+   {
+      if (dp->errset)
+         longjmp(dp->error_return, level);
+
+      else
+         exit(99);
+   }
+}
+
+#if PNG_LIBPNG_VER < 10700 && defined PNG_TEXT_SUPPORTED
+static void
+text_stash(struct display *dp)
+{
+   /* libpng 1.6 and earlier fixed a bug whereby text chunks were written
+    * multiple times by png_write_png; the issue was that png_write_png passed
+    * the same png_info to both png_write_info and png_write_end.  Rather than
+    * fixing it by recording the information in the png_struct, or by recording
+    * where to write the chunks, the fix made was to change the 'compression'
+    * field of the chunk to invalid values, rendering the png_info somewhat
+    * useless.
+    *
+    * The only fix for this given that we use the png_info more than once is to
+    * make a copy of the text chunks and png_set_text it each time.  This adds a
+    * text chunks, so they get replicated, but only the new set gets written
+    * each time.  This uses memory like crazy but there is no way to delete the
+    * useless chunks from the png_info.
+    *
+    * To make this slightly more efficient only the top level structure is
+    * copied; since the old strings are actually preserved (in 1.6 and earlier)
+    * this happens to work.
+    */
+   png_textp chunks = NULL;
+
+   dp->num_text = png_get_text(dp->write_pp, dp->ip, &chunks, NULL);
+
+   if (dp->num_text > 0)
+   {
+      dp->text_ptr = voidcast(png_textp, malloc(dp->num_text * sizeof *chunks));
+
+      if (dp->text_ptr == NULL)
+         display_log(dp, APP_ERROR, "text chunks: stash malloc failed");
+
+      else
+         memcpy(dp->text_ptr, chunks, dp->num_text * sizeof *chunks);
+   }
+
+   dp->text_stashed = 1; /* regardless of whether there are chunks or not */
+}
+
+#define text_stash(dp) if (!dp->text_stashed) text_stash(dp)
+
+static void
+text_restore(struct display *dp)
+{
+   /* libpng makes a copy, so this is fine: */
+   if (dp->text_ptr != NULL)
+      png_set_text(dp->write_pp, dp->ip, dp->text_ptr, dp->num_text);
+}
+
+#define text_restore(dp) if (dp->text_stashed) text_restore(dp)
+
+#else
+#define text_stash(dp) ((void)0)
+#define text_restore(dp) ((void)0)
+#endif /* pre 1.7 */
+
+/* OPTIONS:
+ *
+ * The command handles options of the forms:
+ *
+ *    --option
+ *       Turn an option on (Option)
+ *    --no-option
+ *       Turn an option off (Option)
+ *    --option=value
+ *       Set an option to a value (Value)
+ *    --option=val1,val2,val3
+ *       Set an option to a bitmask constructed from the values (List)
+ */
+static png_byte
+option_index(struct display *dp, const char *opt, size_t len)
+   /* Return the index (in options[]) of the given option, outputs an error if
+    * it does not exist.  Takes the name of the option and a length (number of
+    * characters in the name).
+    */
+{
+   png_byte j;
+
+   for (j=0; j<option_count; ++j)
+      if (strncmp(options[j].name, opt, len) == 0 && options[j].name[len] == 0)
+         return j;
+
+   /* If the setjmp buffer is set the code is asking for an option index; this
+    * is bad.  Otherwise this is the command line option parsing.
+    */
+   display_log(dp, dp->errset ? INTERNAL_ERROR : USER_ERROR,
+         "%.*s: unknown option", (int)/*SAFE*/len, opt);
+   abort(); /* NOT REACHED */
+}
+
+/* This works for an option name (no quotes): */
+#define OPTIND(dp, name) option_index(dp, #name, (sizeof #name)-1)
+
+static int
+get_option(struct display *dp, const char *opt, int *value)
+{
+   const png_byte i = option_index(dp, opt, strlen(opt));
+
+   if (dp->entry[i]) /* option was set on command line */
+   {
+      *value = dp->value[i];
+      return 1;
+   }
+
+   else
+      return 0;
+}
+
+static int
+set_opt_string_(struct display *dp, unsigned int sp, png_byte opt,
+      const char *entry_name)
+   /* Add the appropriate option string to dp->curr. */
+{
+   int offset, add;
+
+   if (sp > 0)
+      offset = dp->stack[sp-1].opt_string_end;
+
+   else
+      offset = dp->opt_string_start;
+
+   if (entry_name == range_lo)
+      add = sprintf(dp->curr+offset, " --%s=%d", options[opt].name,
+            dp->value[opt]);
+
+   else
+      add = sprintf(dp->curr+offset, " --%s=%s", options[opt].name, entry_name);
+
+   if (add < 0)
+      display_log(dp, INTERNAL_ERROR, "sprintf failed");
+
+   assert(offset+add < (int)/*SAFE*/sizeof dp->curr);
+   return offset+add;
+}
+
+static void
+set_opt_string(struct display *dp, unsigned int sp)
+   /* Add the appropriate option string to dp->curr. */
+{
+   dp->stack[sp].opt_string_end = set_opt_string_(dp, sp, dp->stack[sp].opt, 
+      options[dp->stack[sp].opt].values[dp->stack[sp].entry].name);
+}
+
+static void
+record_opt(struct display *dp, png_byte opt, const char *entry_name)
+   /* Record this option in dp->curr; called for an option not being searched,
+    * the caller passes in the name of the value, or range_lo to use the
+    * numerical value.
+    */
+{
+   const unsigned int sp = dp->csp; /* stack entry of next searched option */
+
+   if (sp >= dp->tsp)
+   {
+      /* At top of stack; add the opt string for this entry to the previous
+       * searched entry or the start of the dp->curr buffer if there is nothing
+       * on the stack yet (sp == 0).
+       */
+      const int offset = set_opt_string_(dp, sp, opt, entry_name);
+
+      if (sp > 0)
+         dp->stack[sp-1].opt_string_end = offset;
+
+      else
+         dp->opt_string_start = offset;
+   }
+
+   /* else do nothing: option already recorded */
+}
+
+static int
+opt_list_end(struct display *dp, png_byte opt, png_byte entry)
+{
+   if (options[opt].values[entry].name == range_lo)
+      return entry+1U >= options[opt].value_count /* missing range_hi */ ||
+         options[opt].values[entry+1U].name != range_hi /* likewise */ ||
+         options[opt].values[entry+1U].value <= dp->value[opt] /* range end */;
+
+   else
+      return entry+1U >= options[opt].value_count /* missing 'all' */ ||
+         options[opt].values[entry+1U].name == all /* last entry */;
+}
+
+static void
+push_opt(struct display *dp, unsigned int sp, png_byte opt, int search)
+   /* Push a new option onto the stack, initializing the new stack entry
+    * appropriately; this does all the work of next_opt (setting end/nsp) for
+    * the first entry in the list.
+    */
+{
+   png_byte entry;
+   const char *entry_name;
+
+   assert(sp == dp->tsp && sp < SL);
+
+   /* The starting entry is entry 0 unless there is a range in which case it is
+    * the entry corresponding to range_lo:
+    */
+   entry = options[opt].value_count;
+   assert(entry > 0U);
+
+   do
+   {
+      entry_name = options[opt].values[--entry].name;
+      if (entry_name == range_lo)
+         break;
+   }
+   while (entry > 0U);
+
+   dp->tsp = sp+1U;
+   dp->stack[sp].best_size =
+      dp->stack[sp].lo_size =
+      dp->stack[sp].hi_size = MAX_SIZE;
+
+   if (search && entry_name == range_lo) /* search this range */
+   {
+      dp->stack[sp].lo = options[opt].values[entry].value;
+      /* check for a mal-formed RANGE above: */
+      assert(entry+1 < options[opt].value_count &&
+             options[opt].values[entry+1].name == range_hi);
+      dp->stack[sp].hi = options[opt].values[entry+1].value;
+   }
+
+   else
+   {
+      /* next_opt will just iterate over the range. */
+      dp->stack[sp].lo = INT_MAX;
+      dp->stack[sp].hi = INT_MIN; /* Prevent range chop */
+   }
+
+   dp->stack[sp].opt = opt;
+   dp->stack[sp].entry = entry;
+   dp->stack[sp].best_val = dp->value[opt] = options[opt].values[entry].value;
+
+   set_opt_string(dp, sp);
+
+   /* This works for the search case too; if the range has only one entry 'end'
+    * will be marked here.
+    */
+   if (opt_list_end(dp, opt, entry))
+   {
+      dp->stack[sp].end = 1;
+      /* Skip the warning if pngcp did this itself.  See the code in
+       * set_windowBits_hi.
+       */
+      if (opt != dp->min_windowBits)
+         display_log(dp, APP_WARNING, "%s: only testing one value",
+               options[opt].name);
+   }
+
+   else
+   {
+      dp->stack[sp].end = 0;
+      dp->nsp = dp->tsp;
+   }
+
+   /* Do a lazy cache of the text chunks for libpng 1.6 and earlier; this is
+    * because they can only be written once(!) so if we are going to re-use the
+    * png_info we need a copy.
+    */
+   text_stash(dp);
+}
+
+static void
+next_opt(struct display *dp, unsigned int sp)
+   /* Return the next value for this option.  When called 'sp' is expected to be
+    * the topmost stack entry - only the topmost entry changes each time round -
+    * and there must be a valid entry to return.  next_opt will set dp->nsp to
+    * sp+1 if more entries are available, otherwise it will not change it and
+    * set dp->stack[s].end to true.
+    */
+{
+   int search = 0;
+   png_byte entry, opt;
+   const char *entry_name;
+
+   /* dp->stack[sp] must be the top stack entry and it must be active: */
+   assert(sp+1U == dp->tsp && !dp->stack[sp].end);
+
+   opt = dp->stack[sp].opt;
+   entry = dp->stack[sp].entry;
+   assert(entry+1U < options[opt].value_count);
+   entry_name = options[opt].values[entry].name;
+   assert(entry_name != NULL);
+
+   /* For ranges increment the value but don't change the entry, for all other
+    * cases move to the next entry and load its value:
+    */
+   if (entry_name == range_lo) /* a range */
+   {
+      /* A range can be iterated over or searched.  The default iteration option
+       * is indicated by hi < lo on the stack, otherwise the range being search
+       * is [lo..hi] (inclusive).
+       */
+      if (dp->stack[sp].lo > dp->stack[sp].hi)
+         dp->value[opt]++;
+
+      else
+      {
+         /* This is the best size found for this option value: */
+         png_alloc_size_t best_size = dp->stack[sp].best_size;
+         int lo = dp->stack[sp].lo;
+         int hi = dp->stack[sp].hi;
+         int val = dp->value[opt];
+
+         search = 1; /* end is determined here */
+         assert(best_size < MAX_SIZE);
+
+         if (val == lo)
+         {
+            /* Finding the best for the low end of the range: */
+            dp->stack[sp].lo_size = best_size;
+            assert(hi > val);
+
+            if (hi == val+1) /* only 2 entries */
+               dp->stack[sp].end = 1;
+
+            val = hi;
+         }
+
+         else if (val == hi)
+         {
+            dp->stack[sp].hi_size = best_size;
+            assert(val > lo+1); /* else 'end' set above */
+
+            if (val == lo+2) /* only three entries to test */
+               dp->stack[sp].end = 1;
+
+            val = (lo + val)/2;
+         }
+
+         else
+         {
+            png_alloc_size_t lo_size = dp->stack[sp].lo_size;
+            png_alloc_size_t hi_size = dp->stack[sp].hi_size;
+
+            /* lo and hi should have been tested. */
+            assert(lo_size < MAX_SIZE && hi_size < MAX_SIZE);
+
+            /* These cases arise with the 'probe' handling below when there is a
+             * dip or peak in the size curve.
+             */
+            if (val < lo) /* probing a new lo */
+            {
+               /* Swap lo and val: */
+               dp->stack[sp].lo = val;
+               dp->stack[sp].lo_size = best_size;
+               val = lo;
+               best_size = lo_size;
+               lo = dp->stack[sp].lo;
+               lo_size = dp->stack[sp].lo_size;
+            }
+
+            else if (val > hi) /* probing a new hi */
+            {
+               /* Swap hi and val: */
+               dp->stack[sp].hi = val;
+               dp->stack[sp].hi_size = best_size;
+               val = hi;
+               best_size = hi_size;
+               hi = dp->stack[sp].hi;
+               hi_size = dp->stack[sp].hi_size;
+            }
+
+            /* The following should be true or something got messed up above. */
+            assert(lo < val && val < hi);
+
+            /* If there are only four entries (lo, val, hi plus one more) just
+             * test the remaining entry.
+             */
+            if (hi == lo+3)
+            {
+               /* Because of the 'probe' code val can either be lo+1 or hi-1; we
+                * need to test the other.
+                */
+               val = lo + ((val == lo+1) ? 2 : 1);
+               assert(lo < val && val < hi);
+               dp->stack[sp].end = 1;
+            }
+
+            else
+            {
+               /* There are at least 2 entries still untested between lo and hi,
+                * i.e. hi >= lo+4.  'val' is the midpoint +/- 0.5
+                *
+                * Separate out the four easy cases when lo..val..hi are
+                * monotonically decreased or (more weird) increasing:
+                */
+               assert(hi > lo+3);
+
+               if (lo_size <= best_size && best_size <= hi_size)
+               {
+                  /* Select the low range; testing this first favours the low
+                   * range over the high range when everything comes out equal.
+                   * Because of the probing 'val' may be lo+1.  In that case end
+                   * the search and set 'val' to lo+2.
+                   */
+                  if (val == lo+1)
+                  {
+                     ++val;
+                     dp->stack[sp].end = 1;
+                  }
+
+                  else
+                  {
+                     dp->stack[sp].hi = hi = val;
+                     dp->stack[sp].hi_size = best_size;
+                     val = (lo + val) / 2;
+                  }
+               }
+
+               else if (lo_size >= best_size && best_size >= hi_size)
+               {
+                  /* Monotonically decreasing size; this is the expected case.
+                   * Select the high end of the range.  As above, val may be
+                   * hi-1.
+                   */
+                  if (val == hi-1)
+                  {
+                     --val;
+                     dp->stack[sp].end = 1;
+                  }
+
+                  else
+                  {
+                     dp->stack[sp].lo = lo = val;
+                     dp->stack[sp].lo_size = best_size;
+                     val = (val + hi) / 2;
+                  }
+               }
+
+               /* If both those tests failed 'best_size' is either greater than
+                * or less than both lo_size and hi_size.  There is a peak or dip
+                * in the curve of sizes from lo to hi and val is on the peak or
+                * dip.
+                *
+                * Because the ranges being searched as so small (level is 1..9,
+                * windowBits 8..15, memLevel 1..9) there will only be at most
+                * three untested values between lo..val and val..hi, so solve
+                * the problem by probing down from hi or up from lo, whichever
+                * is the higher.
+                *
+                * This is the place where 'val' is set to outside the range
+                * lo..hi, described as 'probing', though maybe 'narrowing' would
+                * be more accurate.
+                */
+               else if (lo_size <= hi_size) /* down from hi */
+               {
+                  dp->stack[sp].hi = val;
+                  dp->stack[sp].hi_size = best_size;
+                  val = --hi;
+               }
+
+               else /* up from low */
+               {
+                  dp->stack[sp].lo = val;
+                  dp->stack[sp].lo_size = best_size;
+                  val = ++lo;
+               }
+
+               /* lo and hi are still the true range limits, check for the end
+                * condition.
+                */
+               assert(hi > lo+1);
+               if (hi <= lo+2)
+                  dp->stack[sp].end = 1;
+            }
+         }
+
+         assert(val != dp->stack[sp].best_val); /* should be a new value */
+         dp->value[opt] = val;
+         dp->stack[sp].best_size = MAX_SIZE;
+      }
+   }
+
+   else
+   {
+      /* Increment 'entry' */
+      dp->value[opt] = options[opt].values[++entry].value;
+      dp->stack[sp].entry = entry;
+   }
+
+   set_opt_string(dp, sp);
+
+   if (!search && opt_list_end(dp, opt, entry)) /* end of list */
+      dp->stack[sp].end = 1;
+
+   else if (!dp->stack[sp].end) /* still active after all these tests */
+      dp->nsp = dp->tsp;
+}
+
+static int
+compare_option(const struct display *dp, unsigned int sp)
+{
+   int opt = dp->stack[sp].opt;
+
+   /* If the best so far is numerically less than the current value the
+    * current set of options is invariably worse.
+    */
+   if (dp->stack[sp].best_val < dp->value[opt])
+      return -1;
+
+   /* Lists of options are searched out of numerical order (currently only
+    * strategy), so only return +1 here when a range is being searched.
+    */
+   else if (dp->stack[sp].best_val > dp->value[opt])
+   {
+      if (dp->stack[sp].lo <= dp->stack[sp].hi /*searching*/)
+         return 1;
+
+      else
+         return -1;
+   }
+
+   else
+      return 0; /* match; current value is the best one */
+}
+
+static int
+advance_opt(struct display *dp, png_byte opt, int search)
+{
+   unsigned int sp = dp->csp++; /* my stack entry */
+
+   assert(sp >= dp->nsp); /* nsp starts off zero */
+
+   /* If the entry was active in the previous run dp->stack[sp] is already
+    * set up and dp->tsp will be greater than sp, otherwise a new entry
+    * needs to be created.
+    *
+    * dp->nsp is handled this way:
+    *
+    * 1) When an option is pushed onto the stack dp->nsp and dp->tsp are
+    *    both set (by push_opt) to the next stack entry *unless* there is
+    *    only one entry in the new list, in which case dp->stack[sp].end
+    *    is set.
+    *
+    * 2) For the top stack entry next_opt is called.  The entry must be
+    *    active (dp->stack[sp].end is not set) and either 'nsp' or 'end'
+    *    will be updated as appropriate.
+    *
+    * 3) For lower stack entries nsp is set unless the stack entry is
+    *    already at the end.  This means that when all the higher entries
+    *    are popped this entry will be too.
+    */
+   if (sp >= dp->tsp)
+   {
+      push_opt(dp, sp, opt, search); /* This sets tsp to sp+1 */
+      return 1; /* initialized */
+   }
+
+   else
+   {
+      int ret = 0; /* unchanged */
+
+      /* An option that is already on the stack; update best_size and best_val
+       * if appropriate.  On the first run there are no previous values and
+       * dp->write_size will be MAX_SIZE, however on the first run dp->tsp
+       * starts off as 0.
+       */
+      assert(dp->write_size > 0U && dp->write_size < MAX_SIZE);
+
+      if (dp->stack[sp].best_size > dp->write_size ||
+          (dp->stack[sp].best_size == dp->write_size &&
+           compare_option(dp, sp) > 0))
+      {
+         dp->stack[sp].best_size = dp->write_size;
+         dp->stack[sp].best_val = dp->value[opt];
+      }
+
+      if (sp+1U >= dp->tsp)
+      {
+         next_opt(dp, sp);
+         ret = 1; /* advanced */
+      }
+
+      else if (!dp->stack[sp].end) /* Active, not at top of stack */
+         dp->nsp = sp+1U;
+
+      return ret; /* advanced || unchanged */
+   }
+}
+
+static int
+getallopts_(struct display *dp, const png_byte opt, int *value, int record)
+   /* Like getop but iterate over all the values if the option was set to "all".
+    */
+{
+   if (dp->entry[opt]) /* option was set on command line */
+   {
+      /* Simple, single value, entries don't have a stack frame and have a fixed
+       * value (it doesn't change once set on the command line).  Otherwise the
+       * value (entry) selected from the command line is 'all':
+       */
+      const char *entry_name = options[opt].values[dp->entry[opt]-1].name;
+
+      if (entry_name == all)
+         (void)advance_opt(dp, opt, 0/*do not search; iterate*/);
+
+      else if (record)
+         record_opt(dp, opt, entry_name);
+
+      *value = dp->value[opt];
+      return 1; /* set */
+   }
+
+   else
+      return 0; /* not set */
+}
+
+static int
+getallopts(struct display *dp, const char *opt_str, int *value)
+{
+   return getallopts_(dp, option_index(dp, opt_str, strlen(opt_str)), value, 0);
+}
+
+static int
+getsearchopts(struct display *dp, const char *opt_str, int *value)
+   /* As above except that if the option was not set try a search */
+{
+   png_byte istrat;
+   const png_byte opt = option_index(dp, opt_str, strlen(opt_str));
+   int record = options[opt].search;
+   const char *entry_name;
+
+   /* If it was set on the command line honour the setting, including 'all'
+    * which will override the built in search:
+    */
+   if (getallopts_(dp, opt, value, record))
+      return 1;
+
+   else if (!record) /* not a search option */
+      return 0; /* unset and not searched */
+
+   /* Otherwise decide what to do here. */
+   istrat = OPTIND(dp, strategy);
+   entry_name = range_lo; /* record the value, not the name */
+
+   if (opt == istrat) /* search all strategies */
+      (void)advance_opt(dp, opt, 0/*iterate*/), record=0;
+
+   else if (opt == OPTIND(dp, level))
+   {
+      /* Both RLE and HUFFMAN don't benefit from level increases */
+      if (dp->value[istrat] == Z_RLE || dp->value[istrat] == Z_HUFFMAN_ONLY)
+         dp->value[opt] = 1;
+
+      else /* fixed, filtered or default */
+         (void)advance_opt(dp, opt, 1/*search*/), record=0;
+   }
+
+   else if (opt == OPTIND(dp, windowBits))
+   {
+      /* Changing windowBits for strategies that do not search the window is
+       * pointless.  Huffman-only does not search, RLE only searches backwards
+       * one byte, so given that the maximum string length is 258, a windowBits
+       * of 9 is always sufficient.
+       */
+      if (dp->value[istrat] == Z_HUFFMAN_ONLY)
+         dp->value[opt] = 8;
+
+      else if (dp->value[istrat] == Z_RLE)
+         dp->value[opt] = 9;
+
+      else /* fixed, filtered or default */
+         (void)advance_opt(dp, opt, 1/*search*/), record=0;
+   }
+
+   else if (opt == OPTIND(dp, memLevel))
+   {
+#     if 0
+         (void)advance_opt(dp, opt, 0/*all*/), record=0;
+#     else
+         dp->value[opt] = MAX_MEM_LEVEL;
+#     endif
+   }
+
+   else /* something else */
+      assert(0=="reached");
+
+   if (record)
+      record_opt(dp, opt, entry_name);
+
+   /* One of the above searched options: */
+   *value = dp->value[opt];
+   return 1;
+}
+
+static int
+find_val(struct display *dp, png_byte opt, const char *str, size_t len)
+   /* Like option_index but sets (index+i) of the entry in options[opt] that
+    * matches str[0..len-1] into dp->entry[opt] as well as returning the actual
+    * value.
+    */
+{
+   int rlo = INT_MAX, rhi = INT_MIN;
+   png_byte j, irange = 0;
+
+   for (j=1U; j<=options[opt].value_count; ++j)
+   {
+      if (strncmp(options[opt].values[j-1U].name, str, len) == 0 &&
+          options[opt].values[j-1U].name[len] == 0)
+      {
+         dp->entry[opt] = j;
+         return options[opt].values[j-1U].value;
+      }
+      else if (options[opt].values[j-1U].name == range_lo)
+         rlo = options[opt].values[j-1U].value, irange = j;
+      else if (options[opt].values[j-1U].name == range_hi)
+         rhi = options[opt].values[j-1U].value;
+   }
+
+   /* No match on the name, but there may be a range. */
+   if (irange > 0)
+   {
+      char *ep = NULL;
+      long l = strtol(str, &ep, 0);
+
+      if (ep == str+len && l >= rlo && l <= rhi)
+      {
+         dp->entry[opt] = irange; /* range_lo */
+         return (int)/*SAFE*/l;
+      }
+   }
+
+   display_log(dp, dp->errset ? INTERNAL_ERROR : USER_ERROR,
+         "%s: unknown value setting '%.*s'", options[opt].name,
+         (int)/*SAFE*/len, str);
+   abort(); /* NOT REACHED */
+}
+
+static int
+opt_check(struct display *dp, const char *arg)
+{
+   assert(dp->errset == 0);
+
+   if (arg != NULL && arg[0] == '-' && arg[1] == '-')
+   {
+      int i = 0, negate = (strncmp(arg+2, "no-", 3) == 0), val;
+      png_byte j;
+
+      if (negate)
+         arg += 5; /* --no- */
+
+      else
+         arg += 2; /* -- */
+
+      /* Find the length (expect arg\0 or arg=) */
+      while (arg[i] != 0 && arg[i] != '=') ++i;
+
+      /* So arg[0..i-1] is the argument name, this does not return if this isn't
+       * a valid option name.
+       */
+      j = option_index(dp, arg, i);
+
+      /* It matcheth an option; check the remainder. */
+      if (arg[i] == 0) /* no specified value, use the default */
+      {
+         val = options[j].values[negate].value;
+         dp->entry[j] = (png_byte)/*SAFE*/(negate + 1U);
+      }
+
+      else
+      {
+         const char *list = arg + (i+1);
+
+         /* Expect a single value here unless this is a list, in which case
+          * multiple values are combined.
+          */
+         if (options[j].opt != LIST)
+         {
+            /* find_val sets 'dp->entry[j]' to a non-zero value: */
+            val = find_val(dp, j, list, strlen(list));
+
+            if (negate)
+            {
+               if (options[j].opt < OPTION)
+                  val = !val;
+
+               else
+               {
+                  display_log(dp, USER_ERROR,
+                        "%.*s: option=arg cannot be negated", i, arg);
+                  abort(); /* NOT REACHED */
+               }
+            }
+         }
+
+         else /* multiple options separated by ',' characters */
+         {
+            /* --no-option negates list values from the default, which should
+             * therefore be 'all'.  Notice that if the option list is empty in
+             * this case nothing will be removed and therefore --no-option= is
+             * the same as --option.
+             */
+            if (negate)
+               val = options[j].values[0].value;
+
+            else
+               val = 0;
+
+            while (*list != 0) /* allows option= which sets 0 */
+            {
+               /* A value is terminated by the end of the list or a ','
+                * character.
+                */
+               int v, iv;
+
+               iv = 0; /* an index into 'list' */
+               while (list[++iv] != 0 && list[iv] != ',') {}
+
+               v = find_val(dp, j, list, iv);
+
+               if (negate)
+                  val &= ~v;
+
+               else
+                  val |= v;
+
+               list += iv;
+               if (*list != 0)
+                  ++list; /* skip the ',' */
+            }
+         }
+      }
+
+      /* 'val' is the new value, store it for use later and debugging: */
+      dp->value[j] = val;
+
+      if (options[j].opt < LEVEL_MASK)
+      {
+         /* The handling for error levels is to set the level. */
+         if (val) /* Set this level */
+            dp->options = (dp->options & ~LEVEL_MASK) | options[j].opt;
+
+         else
+            display_log(dp, USER_ERROR,
+      "%.*s: messages cannot be turned off individually; set a message level",
+                  i, arg);
+      }
+
+      else if (options[j].opt < OPTION)
+      {
+         if (val)
+            dp->options |= options[j].opt;
+
+         else
+            dp->options &= ~options[j].opt;
+      }
+
+      return 1; /* this is an option */
+   }
+
+   else
+      return 0; /* not an option */
+}
+
+/* The following is used in main to verify that the final argument is a
+ * directory:
+ */
+static int
+checkdir(const char *pathname)
+{
+   struct stat buf;
+   return stat(pathname, &buf) == 0 && S_ISDIR(buf.st_mode);
+}
+
+/* Work out whether a path is valid (if not a display_log occurs), a directory
+ * (1 is returned) or a file *or* non-existent (0 is returned).
+ *
+ * Used for a write path.
+ */
+static int
+isdir(struct display *dp, const char *pathname)
+{
+   if (pathname == NULL)
+      return 0; /* stdout */
+
+   else if (pathname[0] == 0)
+      return 1; /* empty string */
+
+   else
+   {
+      struct stat buf;
+      int ret = stat(pathname, &buf);
+
+      if (ret == 0) /* the entry exists */
+      {
+         if (S_ISDIR(buf.st_mode))
+            return 1;
+
+         /* Else expect an object that exists and can be written: */
+         if (access(pathname, W_OK) != 0)
+            display_log(dp, USER_ERROR, "%s: cannot be written (%s)", pathname,
+                  strerror(errno));
+
+         return 0; /* file (exists, can be written) */
+      }
+
+      else /* an error */
+      {
+         /* Non-existence is fine, other errors are not: */
+         if (errno != ENOENT)
+            display_log(dp, USER_ERROR, "%s: invalid output name (%s)",
+                  pathname, strerror(errno));
+
+         return 0; /* file (does not exist) */
+      }
+   }
+}
+
+static void
+makename(struct display *dp, const char *dir, const char *infile)
+{
+   /* Make a name for an output file (and check it). */
+   dp->namebuf[0] = 0;
+
+   if (dir == NULL || infile == NULL)
+      display_log(dp, INTERNAL_ERROR, "NULL name to makename");
+
+   else
+   {
+      size_t dsize = strlen(dir);
+
+      if (dsize < FILENAME_MAX+2)
+      {
+         size_t isize = strlen(infile);
+         size_t istart = isize-1;
+
+         /* This should fail before here: */
+         if (infile[istart] == '/')
+            display_log(dp, INTERNAL_ERROR, "infile with trailing /");
+
+         memcpy(dp->namebuf, dir, dsize);
+         if (dsize > 0 && dp->namebuf[dsize-1] != '/')
+            dp->namebuf[dsize++] = '/';
+
+         /* Find the rightmost non-/ character: */
+         while (istart > 0 && infile[istart-1] != '/')
+            --istart;
+
+         isize -= istart;
+         infile += istart;
+
+         if (dsize+isize <= FILENAME_MAX)
+         {
+            memcpy(dp->namebuf+dsize, infile, isize+1);
+
+            if (isdir(dp, dp->namebuf))
+               display_log(dp, USER_ERROR, "%s: output file is a directory",
+                     dp->namebuf);
+         }
+
+         else
+         {
+            dp->namebuf[dsize] = 0;
+            display_log(dp, USER_ERROR, "%s%s: output file name too long",
+                  dp->namebuf, infile);
+         }
+      }
+
+      else
+         display_log(dp, USER_ERROR, "%s: output directory name too long", dir);
+   }
+}
+
+/* error handler callbacks for libpng */
+static void PNGCBAPI
+display_warning(png_structp pp, png_const_charp warning)
+{
+   struct display *dp = get_dp(pp);
+
+   /* This is used to prevent repeated warnings while searching */
+   if (!dp->no_warnings)
+      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_start_read(struct display *dp, const char *filename)
+{
+   if (filename != NULL)
+   {
+      dp->filename = filename;
+      dp->fp = fopen(filename, "rb");
+   }
+
+   else
+   {
+      dp->filename = "<stdin>";
+      dp->fp = stdin;
+   }
+
+   dp->w = dp->h = 0U;
+   dp->bpp = 0U;
+   dp->size = 0U;
+   dp->read_size = 0U;
+
+   if (dp->fp == NULL)
+      display_log(dp, USER_ERROR, "file open failed (%s)", strerror(errno));
+}
+
+static void PNGCBAPI
+read_function(png_structp pp, png_bytep data, png_size_t size)
+{
+   struct display *dp = get_dp(pp);
+
+   if (size == 0U || fread(data, size, 1U, dp->fp) == 1U)
+      dp->read_size += size;
+
+   else
+   {
+      if (feof(dp->fp))
+         display_log(dp, LIBPNG_ERROR, "PNG file truncated");
+      else
+         display_log(dp, LIBPNG_ERROR, "PNG file read failed (%s)",
+               strerror(errno));
+   }
+}
+
+static void
+read_png(struct display *dp, const char *filename)
+{
+   display_clean_read(dp); /* safety */
+   display_start_read(dp, filename);
+
+   dp->read_pp = png_create_read_struct(PNG_LIBPNG_VER_STRING, dp,
+      display_error, display_warning);
+   if (dp->read_pp == NULL)
+      display_log(dp, LIBPNG_ERROR, "failed to create read struct");
+
+#  ifdef PNG_BENIGN_ERRORS_SUPPORTED
+      png_set_benign_errors(dp->read_pp, 1/*allowed*/);
+#  endif /* BENIGN_ERRORS */
+
+#  ifdef FIX_INDEX
+      if ((dp->options & FIX_INDEX) != 0)
+         png_set_check_for_invalid_index(dp->read_pp, 1/*on, no warning*/);
+#     ifdef IGNORE_INDEX
+         else
+#     endif /* IGNORE_INDEX */
+#  endif /* FIX_INDEX */
+#  ifdef IGNORE_INDEX
+      if ((dp->options & IGNORE_INDEX) != 0) /* DANGEROUS */
+         png_set_check_for_invalid_index(dp->read_pp, -1/*off completely*/);
+#  endif /* IGNORE_INDEX */
+
+   /* The png_read_png API requires us to make the info struct, but it does the
+    * call to png_read_info.
+    */
+   dp->ip = png_create_info_struct(dp->read_pp);
+   if (dp->ip == NULL)
+      png_error(dp->read_pp, "failed to create info struct");
+
+   /* Set the IO handling */
+   png_set_read_fn(dp->read_pp, dp, read_function);
+
+#  ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+      png_set_keep_unknown_chunks(dp->read_pp, PNG_HANDLE_CHUNK_ALWAYS, NULL,
+            0);
+#  endif /* HANDLE_AS_UNKNOWN */
+
+#  ifdef PNG_SET_USER_LIMITS_SUPPORTED
+      /* Remove the user limits, if any */
+      png_set_user_limits(dp->read_pp, 0x7fffffff, 0x7fffffff);
+#  endif /* SET_USER_LIMITS */
+
+   /* Now read the PNG. */
+   png_read_png(dp->read_pp, dp->ip, 0U/*transforms*/, NULL/*params*/);
+   dp->w = png_get_image_width(dp->read_pp, dp->ip);
+   dp->h = png_get_image_height(dp->read_pp, dp->ip);
+   dp->ct = png_get_color_type(dp->read_pp, dp->ip);
+   dp->bpp = png_get_bit_depth(dp->read_pp, dp->ip) *
+             png_get_channels(dp->read_pp, dp->ip);
+   {
+      png_alloc_size_t rb = png_get_rowbytes(dp->read_pp, dp->ip);
+
+      /* The size calc can overflow. */
+      if ((MAX_SIZE-dp->h)/rb < dp->h)
+         png_error(dp->read_pp, "image too large");
+
+      dp->size = rb * dp->h + dp->h/*filter byte*/;
+   }
+
+#ifdef FIX_INDEX
+   if (dp->ct == PNG_COLOR_TYPE_PALETTE && (dp->options & FIX_INDEX) != 0)
+   {
+      int max = png_get_palette_max(dp->read_pp, dp->ip);
+      png_colorp palette = NULL;
+      int num = -1;
+
+      if (png_get_PLTE(dp->read_pp, dp->ip, &palette, &num) != PNG_INFO_PLTE
+          || max < 0 || num <= 0 || palette == NULL)
+         display_log(dp, LIBPNG_ERROR, "invalid png_get_PLTE result");
+
+      if (max >= num)
+      {
+         /* 'Fix' the palette. */
+         int i;
+         png_color newpal[256];
+
+         for (i=0; i<num; ++i)
+            newpal[i] = palette[i];
+
+         /* Fill in any remainder with a warning color: */
+         for (; i<=max; ++i)
+         {
+            newpal[i].red = 0xbe;
+            newpal[i].green = 0xad;
+            newpal[i].blue = 0xed;
+         }
+
+         png_set_PLTE(dp->read_pp, dp->ip, newpal, i);
+      }
+   }
+#endif /* FIX_INDEX */
+
+   display_clean_read(dp);
+   dp->operation = "none";
+}
+
+static void
+display_start_write(struct display *dp, const char *filename)
+{
+   assert(dp->fp == NULL);
+
+   if ((dp->options & NOWRITE) != 0)
+      dp->output_file = "<no write>";
+
+   else
+   {
+      if (filename != NULL)
+      {
+         dp->output_file = filename;
+         dp->fp = fopen(filename, "wb");
+      }
+
+      else
+      {
+         dp->output_file = "<stdout>";
+         dp->fp = stdout;
+      }
+
+      if (dp->fp == NULL)
+         display_log(dp, USER_ERROR, "%s: file open failed (%s)",
+               dp->output_file, strerror(errno));
+   }
+}
+
+static void PNGCBAPI
+write_function(png_structp pp, png_bytep data, png_size_t size)
+{
+   struct display *dp = get_dp(pp);
+
+   /* The write fail is classed as a USER_ERROR, so --quiet does not turn it
+    * off, this seems more likely to be correct.
+    */
+   if (dp->fp == NULL || fwrite(data, size, 1U, dp->fp) == 1U)
+   {
+      dp->write_size += size;
+      if (dp->write_size < size || dp->write_size == MAX_SIZE)
+         png_error(pp, "IDAT size overflow");
+   }
+
+   else
+      display_log(dp, USER_ERROR, "%s: PNG file write failed (%s)",
+            dp->output_file, strerror(errno));
+}
+
+/* Compression option, 'method' is never set: there is no choice.
+ *
+ * IMPORTANT: the order of the entries in this macro determines the preference
+ * order when two different combos of two of these options produce an IDAT of
+ * the same size.  The logic here is to put the things that affect the decoding
+ * of the PNG image ahead of those that are relevant only to the encoding.
+ */
+#define SET_COMPRESSION\
+   SET(strategy, strategy);\
+   SET(windowBits, window_bits);\
+   SET(level, level);\
+   SET(memLevel, mem_level);
+
+#ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
+static void
+search_compression(struct display *dp)
+{
+   /* Like set_compression below but use a more restricted search than 'all' */
+   int val;
+
+#  define SET(name, func) if (getsearchopts(dp, #name, &val))\
+      png_set_compression_ ## func(dp->write_pp, val);
+   SET_COMPRESSION
+#  undef SET
+}
+
+static void
+set_compression(struct display *dp)
+{
+   int val;
+
+#  define SET(name, func) if (getallopts(dp, #name, &val))\
+      png_set_compression_ ## func(dp->write_pp, val);
+   SET_COMPRESSION
+#  undef SET
+}
+
+#ifdef PNG_SW_COMPRESS_level /* 1.7.0+ */
+static void
+set_ICC_profile_compression(struct display *dp)
+{
+   int val;
+
+#  define SET(name, func) if (getallopts(dp, "ICC-profile-" #name, &val))\
+      png_set_ICC_profile_compression_ ## func(dp->write_pp, val);
+   SET_COMPRESSION
+#  undef SET
+}
+#else
+#  define set_ICC_profile_compression(dp) ((void)0)
+#endif
+#else
+#  define search_compression(dp) ((void)0)
+#  define set_compression(dp) ((void)0)
+#  define set_ICC_profile_compression(dp) ((void)0)
+#endif /* WRITE_CUSTOMIZE_COMPRESSION */
+
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
+static void
+set_text_compression(struct display *dp)
+{
+   int val;
+
+#  define SET(name, func) if (getallopts(dp, "text-" #name, &val))\
+      png_set_text_compression_ ## func(dp->write_pp, val);
+   SET_COMPRESSION
+#  undef SET
+}
+#else
+#  define set_text_compression(dp) ((void)0)
+#endif /* WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+
+static void
+write_png(struct display *dp, const char *destname)
+{
+   display_clean_write(dp); /* safety */
+   display_start_write(dp, destname);
+
+   dp->write_pp = png_create_write_struct(PNG_LIBPNG_VER_STRING, dp,
+      display_error, display_warning);
+
+   if (dp->write_pp == NULL)
+      display_log(dp, LIBPNG_ERROR, "failed to create write png_struct");
+
+#  ifdef PNG_BENIGN_ERRORS_SUPPORTED
+      png_set_benign_errors(dp->write_pp, 1/*allowed*/);
+#  endif /* BENIGN_ERRORS */
+
+   png_set_write_fn(dp->write_pp, dp, write_function, NULL/*flush*/);
+
+#ifdef IGNORE_INDEX
+   if ((dp->options & IGNORE_INDEX) != 0) /* DANGEROUS */
+      png_set_check_for_invalid_index(dp->write_pp, -1/*off completely*/);
+#endif /* IGNORE_INDEX */
+
+   /* Restore the text chunks when using libpng 1.6 or less; this is a macro
+    * which expands to nothing in 1.7+  In earlier versions it tests
+    * dp->text_stashed, which is only set (below) *after* the first write.
+    */
+   text_restore(dp);
+
+#  ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+      png_set_keep_unknown_chunks(dp->write_pp, PNG_HANDLE_CHUNK_ALWAYS, NULL,
+            0);
+#  endif /* HANDLE_AS_UNKNOWN */
+
+#  ifdef PNG_SET_USER_LIMITS_SUPPORTED
+      /* Remove the user limits, if any */
+      png_set_user_limits(dp->write_pp, 0x7fffffff, 0x7fffffff);
+#  endif
+
+   /* OPTION HANDLING */
+   /* compression outputs, IDAT and zTXt/iTXt: */
+   dp->tsp = dp->nsp;
+   dp->nsp = dp->csp = 0;
+#  ifdef PNG_SW_COMPRESS_png_level
+      {
+         int val;
+
+         /* This sets everything, but then the following options just override
+          * the specific settings for ICC profiles and text.
+          */
+         if (getallopts(dp, "compression", &val))
+            png_set_compression(dp->write_pp, val);
+
+         if (getallopts(dp, "ICC-profile-compression", &val))
+            png_set_ICC_profile_compression(dp->write_pp, val);
+
+         if (getallopts(dp, "text-compression", &val))
+            png_set_text_compression(dp->write_pp, val);
+      }
+#  endif /* png_level support */
+   if (dp->options & SEARCH)
+      search_compression(dp);
+   else
+      set_compression(dp);
+   set_ICC_profile_compression(dp);
+   set_text_compression(dp);
+
+   {
+      int val;
+
+      /* The permitted range is 1..0x7FFFFFFF, so the cast is safe */
+      if (get_option(dp, "IDAT-size", &val))
+         png_set_IDAT_size(dp->write_pp, val);
+   }
+
+   /* filter handling */
+#  ifdef PNG_WRITE_FILTER_SUPPORTED
+      {
+         int val;
+
+         if (get_option(dp, "filter", &val))
+            png_set_filter(dp->write_pp, PNG_FILTER_TYPE_BASE, val);
+      }
+#  endif /* WRITE_FILTER */
+
+   /* This just uses the 'read' info_struct directly, it contains the image. */
+   dp->write_size = 0U;
+   png_write_png(dp->write_pp, dp->ip, 0U/*transforms*/, NULL/*params*/);
+
+   /* Make sure the file was written ok: */
+   if (dp->fp != NULL)
+   {
+      FILE *fp = dp->fp;
+      dp->fp = NULL;
+      if (fclose(fp))
+         display_log(dp, APP_ERROR, "%s: write failed (%s)",
+               destname == NULL ? "stdout" : destname, strerror(errno));
+   }
+
+   /* Clean it on the way out - if control returns to the caller then the
+    * written_file contains the required data.
+    */
+   display_clean_write(dp);
+   dp->operation = "none";
+}
+
+static void
+set_windowBits_hi(struct display *dp)
+{
+   /* windowBits is in the range 8..15 but zlib maps '8' to '9' so it is only
+    * worth using if the data size is 256 byte or less.
+    */
+   int wb = MAX_WBITS; /* for large images */
+   int i = VLSIZE(windowBits_IDAT);
+
+   while (wb > 8 && dp->size <= 1U<<(wb-1)) --wb;
+
+   while (--i >= 0) if (VLNAME(windowBits_IDAT)[i].name == range_hi) break;
+
+   assert(i > 1); /* vl_windowBits_IDAT always has a RANGE() */
+   VLNAME(windowBits_IDAT)[i].value = wb;
+
+   assert(VLNAME(windowBits_IDAT)[--i].name == range_lo);
+   VLNAME(windowBits_IDAT)[i].value = wb > 8 ? 9 : 8;
+
+   /* If wb == 8 then any search has been restricted to just one windowBits
+    * entry.  Record that here to avoid producing a spurious app-level warning
+    * above.
+    */
+   if (wb == 8)
+      dp->min_windowBits = OPTIND(dp, windowBits);
+}
+
+static int
+better_options(const struct display *dp)
+{
+   /* Are these options better than the best found so far?  Normally the
+    * options are tested in preference order, best first, however when doing a
+    * search operation on a range the range values are tested out of order.  In
+    * that case preferable options will get tested later.
+    *
+    * This function looks through the stack from the bottom up looking for an
+    * option that does not match the current best value.  When it finds one it
+    * checks to see if it is more or less desireable and returns true or false
+    * as appropriate.
+    *
+    * Notice that this means that the order options are pushed onto the stack
+    * conveys a priority; lower/earlier options are more important than later
+    * ones.
+    */
+   unsigned int sp;
+
+   for (sp=0; sp<dp->csp; ++sp)
+   {
+      int c = compare_option(dp, sp);
+
+      if (c < 0)
+         return 0; /* worse */
+
+      else if (c > 0)
+         return 1; /* better */
+   }
+
+   assert(0 && "unreached");
+}
+
+static void
+print_search_results(struct display *dp)
+{
+   assert(dp->filename != NULL);
+   printf("%s [%ld x %ld %d bpp %s, %lu bytes] %lu -> %lu with '%s'\n",
+      dp->filename, (unsigned long)dp->w, (unsigned long)dp->h, dp->bpp,
+      cts(dp->ct), (unsigned long)dp->size, (unsigned long)dp->read_size,
+      (unsigned long)dp->best_size, dp->best);
+   fflush(stdout);
+}
+
+static void
+log_search(struct display *dp, unsigned int log_depth)
+{
+   /* Log, and reset, the search so far: */
+   if (dp->nsp/*next entry to change*/ <= log_depth)
+   {
+      print_search_results(dp);
+      /* Start again with this entry: */
+      dp->best_size = MAX_SIZE;
+   }
+}
+
+static void
+cp_one_file(struct display *dp, const char *filename, const char *destname)
+{
+   unsigned int log_depth;
+
+   dp->filename = filename;
+   dp->operation = "read";
+   dp->no_warnings = 0;
+
+   /* Read it then write it: */
+   if (filename != NULL && access(filename, R_OK) != 0)
+      display_log(dp, USER_ERROR, "%s: invalid file name (%s)",
+            filename, strerror(errno));
+
+   read_png(dp, filename);
+
+   /* But 'destname' may be a directory. */
+   dp->operation = "write";
+
+   /* Limit the upper end of the windowBits range for this file */
+   set_windowBits_hi(dp);
+
+   /* For logging, depth to log: */
+   {
+      int val;
+
+      if (get_option(dp, "log-depth", &val) && val >= 0)
+         log_depth = (unsigned int)/*SAFE*/val;
+
+      else
+         log_depth = 0U;
+   }
+
+   if (destname != NULL) /* else stdout */
+   {
+      if (isdir(dp, destname))
+      {
+         makename(dp, destname, filename);
+         destname = dp->namebuf;
+      }
+
+      else if (access(destname, W_OK) != 0 && errno != ENOENT)
+         display_log(dp, USER_ERROR, "%s: invalid output name (%s)", destname,
+               strerror(errno));
+   }
+
+   dp->nsp = 0;
+   dp->curr[0] = 0; /* acts as a flag for the caller */
+   dp->opt_string_start = 0;
+   dp->best[0] = 0; /* safety */
+   dp->best_size = MAX_SIZE;
+   write_png(dp, destname);
+
+   /* Initialize the 'best' fields: */
+   strcpy(dp->best, dp->curr);
+   dp->best_size = dp->write_size;
+
+   if (dp->nsp > 0) /* interating over lists */
+   {
+      char *tmpname, tmpbuf[(sizeof dp->namebuf) + 4];
+      assert(dp->curr[0] == ' ' && dp->tsp > 0);
+
+      /* Cancel warnings on subsequent writes */
+      log_search(dp, log_depth);
+      dp->no_warnings = 1;
+
+      /* Make a temporary name for the subsequent tests: */
+      if (destname != NULL)
+      {
+         strcpy(tmpbuf, destname);
+         strcat(tmpbuf, ".tmp"); /* space for .tmp allocated above */
+         tmpname = tmpbuf;
+      }
+
+      else
+         tmpname = NULL; /* stdout */
+
+      /* Loop to find the best option. */
+      do
+      {
+         write_png(dp, tmpname);
+
+         /* And compare the sizes (the write function makes sure write_size
+          * doesn't overflow.)
+          */
+         assert(dp->csp > 0);
+
+         if (dp->write_size < dp->best_size ||
+             (dp->write_size == dp->best_size && better_options(dp)))
+         {
+            if (destname != NULL && rename(tmpname, destname) != 0)
+               display_log(dp, APP_ERROR, "rename %s %s failed (%s)", tmpname,
+                     destname, strerror(errno));
+
+            strcpy(dp->best, dp->curr);
+            dp->best_size = dp->write_size;
+         }
+
+         else if (tmpname != NULL && unlink(tmpname) != 0)
+            display_log(dp, APP_WARNING, "unlink %s failed (%s)", tmpname,
+                  strerror(errno));
+
+         log_search(dp, log_depth);
+      }
+      while (dp->nsp > 0);
+
+      /* Do this for the 'sizes' option so that it reports the correct size. */
+      dp->write_size = dp->best_size;
+   }
+}
+
+static int
+cppng(struct display *dp, const char *file, const char *gv dest)
+   /* Exists solely to isolate the setjmp clobbers which some versions of GCC
+    * erroneously generate.
+    */
+{
+   int ret = setjmp(dp->error_return);
+
+   if (ret == 0)
+   {
+      dp->errset = 1;
+      cp_one_file(dp, file, dest);
+      dp->errset = 0;
+      return 0;
+   }
+
+   else
+   {
+      dp->errset = 0;
+
+      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;
+   struct display d;
+
+   display_init(&d);
+
+   d.operation = "options";
+   for (option_end = 1;
+        option_end < argc && opt_check(&d, argv[option_end]);
+        ++option_end)
+   {
+   }
+
+   /* Do a quick check on the directory target case; when there are more than
+    * two arguments the last one must be a directory.
+    */
+   if (!(d.options & NOWRITE) && option_end+2 < argc && !checkdir(argv[argc-1]))
+   {
+      fprintf(stderr,
+            "pngcp: %s: directory required with more than two arguments\n",
+            argv[argc-1]);
+      return 99;
+   }
+
+   {
+      int errors = 0;
+      int i = option_end;
+
+      /* Do this at least once; if there are no arguments stdin/stdout are used.
+       */
+      d.operation = "files";
+      do
+      {
+         const char *infile = NULL;
+         const char *outfile = NULL;
+         int ret;
+
+         if (i < argc)
+         {
+            infile = argv[i++];
+            if (!(d.options & NOWRITE) && i < argc)
+               outfile = argv[argc-1];
+         }
+
+         ret = cppng(&d, infile, outfile);
+
+         if (ret)
+         {
+            if (ret > QUIET) /* abort on user or internal error */
+               return 99;
+
+            /* An error: the output is meaningless */
+         }
+
+         else if (d.best[0] != 0)
+         {
+            /* This result may already have been output, in which case best_size
+             * has been reset.
+             */
+            if (d.best_size < MAX_SIZE)
+               print_search_results(&d);
+         }
+
+         else if (d.options & SIZES)
+         {
+            printf("%s [%ld x %ld %d bpp %s, %lu bytes] %lu -> %lu [0x%lx]\n",
+                  infile, (unsigned long)d.w, (unsigned long)d.h, d.bpp,
+                  cts(d.ct), (unsigned long)d.size, (unsigned long)d.read_size,
+                  (unsigned long)d.write_size, (unsigned long)d.results);
+            fflush(stdout);
+         }
+
+         /* 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: pngcp", pass ? "PASS" : "FAIL");
+
+               for (j=1; j<option_end; ++j)
+                  printf(" %s", argv[j]);
+
+               if (infile != NULL)
+                  printf(" %s", infile);
+
+               printf("\n");
+               fflush(stdout);
+            }
+         }
+
+         display_clean(&d);
+      }
+      while (i+!(d.options & NOWRITE) < argc);
+         /* I.e. for write cases after the first time through the loop require
+          * there to be at least two arguments left and for the last one to be a
+          * directory (this was checked above).
+          */
+
+      /* Release allocated memory */
+      display_destroy(&d);
+
+      return errors != 0;
+   }
+}
+#else /* !READ_PNG || !WRITE_PNG */
+int
+main(void)
+{
+   fprintf(stderr, "pngcp: no support for png_read/write_image\n");
+   return 77;
+}
+#endif /* !READ_PNG || !WRITE_PNG */
diff --git a/png.h b/png.h
index 814f900d3..5574ed799 100644
--- a/png.h
+++ b/png.h
@@ -2300,8 +2300,10 @@ PNG_EXPORT(171, void, png_set_sCAL_s, (png_const_structrp png_ptr,
  *    except for the IHDR, PLTE, tRNS, IDAT, and IEND chunks (which continue to
  *    be processed by libpng.
  */
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 PNG_EXPORT(172, void, png_set_keep_unknown_chunks, (png_structrp png_ptr,
     int keep, png_const_bytep chunk_list, int num_chunks));
+#endif /* HANDLE_AS_UNKNOWN */
 
 /* The "keep" PNG_HANDLE_CHUNK_ parameter for the specified chunk is returned;
  * the result is therefore true (non-zero) if special handling is required,
@@ -2309,7 +2311,7 @@ PNG_EXPORT(172, void, png_set_keep_unknown_chunks, (png_structrp png_ptr,
  */
 PNG_EXPORT(173, int, png_handle_as_unknown, (png_const_structrp png_ptr,
     png_const_bytep chunk_name));
-#endif
+#endif /* SET_UNKNOWN_CHUNKS */
 
 #ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
 PNG_EXPORT(174, void, png_set_unknown_chunks, (png_const_structrp png_ptr,
diff --git a/pngset.c b/pngset.c
index 43456b729..5ffb28364 100644
--- a/pngset.c
+++ b/pngset.c
@@ -1662,7 +1662,9 @@ png_set_check_for_invalid_index(png_structrp png_ptr, int allowed)
 png_uint_32 /* PRIVATE */
 png_check_keyword(png_structrp png_ptr, png_const_charp key, png_bytep new_key)
 {
+#ifdef PNG_WARNINGS_SUPPORTED
    png_const_charp orig_key = key;
+#endif
    png_uint_32 key_len = 0;
    int bad_character = 0;
    int space = 1;
@@ -1725,7 +1727,9 @@ png_check_keyword(png_structrp png_ptr, png_const_charp key, png_bytep new_key)
 
       png_formatted_warning(png_ptr, p, "keyword \"@1\": bad character '0x@2'");
    }
-#endif /* WARNINGS */
+#else /* !WARNINGS */
+   PNG_UNUSED(png_ptr)
+#endif /* !WARNINGS */
 
    return key_len;
 }
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index 2c936c22f..019c06d47 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -552,6 +552,7 @@ option WRITE_ANCILLARY_CHUNKS requires WRITE
 
 # These options disable *all* the text chunks if turned off
 
+option TEXT disabled
 option READ_TEXT requires READ_ANCILLARY_CHUNKS enables TEXT
 option WRITE_TEXT requires WRITE_ANCILLARY_CHUNKS enables TEXT