/* makepng.c
 *
 * Copyright (c) 2012 John Cunningham Bowler
 *
 * Last changed in libpng 1.6.0 [(PENDING RELEASE)]
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * Make a test PNG image.  The arguments are as follows:
 *
 *  makepng [--sRGB|--linear|--1.8] color-type bit-depth [file-name]
 *
 * The color-type may be numeric (and must match the numbers used by the PNG
 * specification) or one of the format names listed below.  The bit-depth is the
 * component bit depth, or the pixel bit-depth for a color-mapped image.
 *
 * Without any options no color-space information is written, with the options
 * an sRGB or the appropriate gAMA chunk is written.  "1.8" refers to the
 * display system used on older Apple computers to correct for high ambient
 * light levels in the viewing environment; it applies a transform of
 * approximately value^(1/1.45) to the color values and so a gAMA chunk of 65909
 * is written (1.45/2.2).
 *
 * The image data is generated internally.  The images used are as follows:
 *
 * 1 channel: a square image with a diamond, the least luminous colors are on
 *    the edge of the image, the most luminous in the center.
 *
 * 2 channels: the color channel increases in luminosity from top to bottom, the
 *    alpha channel increases in opacity from left to right.
 *
 * 3 channels: linear combinations of, from the top-left corner clockwise,
 *    black, green, white, red.
 *
 * 4 channels: linear combinations of, from the top-left corner clockwise,
 *    transparent, red, green, blue.
 *
 * For color-mapped images a four channel color-map is used and the PNG file has
 * a tRNS chunk, as follows:
 *
 * 1-bit: entry 0 is transparent-red, entry 1 is opaque-white
 * 2-bit: entry 0: transparent-green
 *        entry 1: 40%-red
 *        entry 2: 80%-blue
 *        entry 3: opaque-white
 * 4-bit: the 16 combinations of the 2-bit case
 * 8-bit: the 256 combinations of the 4-bit case
 *
 * The palette always has 2^bit-depth entries and the tRNS chunk one fewer.  The
 * image is the 1-channel diamond, but using palette index, not luminosity.
 *
 * Image size is determined by the final pixel depth in bits, i.e. channels x
 * bit-depth, as follows:
 *
 * 8 bits or less:    64x64
 * 16 bits:           256x256
 * More than 16 bits: 1024x1024
 *
 * Row filtering is turned off (the 'none' filter is used on every row) and  the
 * images are not interlaced.
 *
 * If file-name is given then the PNG is written to that file, else it is
 * written to stdout.  Notice that stdout is not supported on systems where, by
 * default, it assumes text output; this program makes no attempt to change the
 * text mode of stdout!
 */
#define _ISOC99_SOURCE /* for strtoull */

#include <stddef.h> /* for offsetof */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <errno.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

/* This structure is used for inserting extra chunks (the --insert argument, not
 * documented above.)
 */
typedef struct chunk_insert
{
   struct chunk_insert *next;
   void               (*insert)(png_structp, png_infop, int, png_charpp);
   int                  nparams;
   png_charp            parameters[1];
} chunk_insert;

static int
channels_of_type(int color_type)
{
   if (color_type & PNG_COLOR_MASK_PALETTE)
      return 1;

   else
   {
      int channels = 1;

      if (color_type & PNG_COLOR_MASK_COLOR)
         channels = 3;

      if (color_type & PNG_COLOR_MASK_ALPHA)
         return channels + 1;

      else
         return channels;
   }
}

static int
pixel_depth_of_type(int color_type, int bit_depth)
{
   return channels_of_type(color_type) * bit_depth;
}

static unsigned int
image_size_of_type(int color_type, int bit_depth)
{
   int pixel_depth = pixel_depth_of_type(color_type, bit_depth);

   if (pixel_depth < 8)
      return 64;

   else if (pixel_depth > 16)
      return 1024;

   else
      return 256;
}

static void
set_color(png_colorp color, png_bytep trans, unsigned int red,
   unsigned int green, unsigned int blue, unsigned int alpha,
   png_const_bytep gamma_table)
{
   color->red = gamma_table[red];
   color->green = gamma_table[green];
   color->blue = gamma_table[blue];
   *trans = (png_byte)alpha;
}

static int
generate_palette(png_colorp palette, png_bytep trans, int bit_depth,
   png_const_bytep gamma_table)
{
   /*
    * 1-bit: entry 0 is transparent-red, entry 1 is opaque-white
    * 2-bit: entry 0: transparent-green
    *        entry 1: 40%-red
    *        entry 2: 80%-blue
    *        entry 3: opaque-white
    * 4-bit: the 16 combinations of the 2-bit case
    * 8-bit: the 256 combinations of the 4-bit case
    */
   if (bit_depth == 1)
   {
      set_color(palette+0, trans+0, 255, 0, 0, 0, gamma_table);
      set_color(palette+1, trans+1, 255, 255, 255, 255, gamma_table);
      return 2;
   }

   else
   {
      unsigned int size = 1U << (bit_depth/2); /* 2, 4 or 16 */
      unsigned int x, y, ip;

      for (x=0; x<size; ++x) for (y=0; y<size; ++y)
      {
         ip = x + (size * y);

         /* size is at most 16, so the scaled value below fits in 16 bits */
#        define interp(pos, c1, c2) ((pos * c1) + ((size-pos) * c2))
#        define xyinterp(x, y, c1, c2, c3, c4) (((size * size / 2) +\
            (interp(x, c1, c2) * y + (size-y) * interp(x, c3, c4))) /\
            (size*size))

         set_color(palette+ip, trans+ip,
            /* color:    green, red,blue,white */
            xyinterp(x, y,   0, 255,   0, 255),
            xyinterp(x, y, 255,   0,   0, 255),
            xyinterp(x, y,   0,   0, 255, 255),
            /* alpha:        0, 102, 204, 255) */
            xyinterp(x, y,   0, 102, 204, 255),
            gamma_table);
      }

      return ip+1;
   }
}

static void
set_value(png_bytep row, size_t rowbytes, png_uint_32 x, unsigned int bit_depth,
   png_uint_32 value, png_const_bytep gamma_table, double conv)
{
   unsigned int mask = (1U << bit_depth)-1;

   x *= bit_depth;  /* Maxium x is 4*1024, maxium bit_depth is 16 */

   if (value <= mask)
   {
      png_uint_32 offset = x >> 3;

      if (offset < rowbytes && (bit_depth < 16 || offset+1 < rowbytes))
      {
         row += offset;

         switch (bit_depth)
         {
            case 1:
            case 2:
            case 4:
               /* Don't gamma correct - values get smashed */
               {
                  unsigned int shift = (8 - bit_depth) - (x & 0x7U);

                  mask <<= shift;
                  value = (value << shift) & mask;
                  *row = (png_byte)((*row & ~mask) | value);
               }
               return;

            default:
               fprintf(stderr, "makepng: bad bit depth (internal error)\n");
               exit(1);

            case 16:
               value = (unsigned int)floor(65535*pow(value/65535.,conv)+.5);
               *row++ = (png_byte)(value >> 8);
               *row = (png_byte)value;
               return;

            case 8:
               *row = gamma_table[value];
               return;
         }
      }

      else
      {
         fprintf(stderr, "makepng: row buffer overflow (internal error)\n");
         exit(1);
      }
   }

   else
   {
      fprintf(stderr, "makepng: component overflow (internal error)\n");
      exit(1);
   }
}

static void
generate_row(png_bytep row, size_t rowbytes, unsigned int y, int color_type,
   int bit_depth, png_const_bytep gamma_table, double conv)
{
   png_uint_32 size_max = image_size_of_type(color_type, bit_depth)-1;
   png_uint_32 depth_max = (1U << bit_depth)-1; /* up to 65536 */

   switch (channels_of_type(color_type))
   {
   /* 1 channel: a square image with a diamond, the least luminous colors are on
    *    the edge of the image, the most luminous in the center.
    */
      case 1:
         {
            png_uint_32 x;
            png_uint_32 base = 2*size_max - abs(2*y-size_max);

            for (x=0; x<=size_max; ++x)
            {
               png_uint_32 luma = base - abs(2*x-size_max);

               /* 'luma' is now in the range 0..2*size_max, we need
                * 0..depth_max
                */
               luma = (luma*depth_max + size_max) / (2*size_max);
               set_value(row, rowbytes, x, bit_depth, luma, gamma_table, conv);
            }
         }
         break;

   /* 2 channels: the color channel increases in luminosity from top to bottom,
    *    the alpha channel increases in opacity from left to right.
    */
      case 2:
         {
            png_uint_32 alpha = (depth_max * y * 2 + size_max) / (2 * size_max);
            png_uint_32 x;

            for (x=0; x<=size_max; ++x)
            {
               set_value(row, rowbytes, 2*x, bit_depth,
                  (depth_max * x * 2 + size_max) / (2 * size_max), gamma_table,
                  conv);
               set_value(row, rowbytes, 2*x+1, bit_depth, alpha, gamma_table,
                  conv);
            }
         }
         break;

   /* 3 channels: linear combinations of, from the top-left corner clockwise,
    *    black, green, white, red.
    */
      case 3:
         {
            /* x0: the black->red scale (the value of the red component) at the
             *     start of the row (blue and green are 0).
             * x1: the green->white scale (the value of the red and blue
             *     components at the end of the row; green is depth_max).
             */
            png_uint_32 Y = (depth_max * y * 2 + size_max) / (2 * size_max);
            png_uint_32 x;

            /* Interpolate x/depth_max from start to end:
             *
             *        start end         difference
             * red:     Y    Y            0
             * green:   0   depth_max   depth_max
             * blue:    0    Y            Y
             */
            for (x=0; x<=size_max; ++x)
            {
               set_value(row, rowbytes, 3*x+0, bit_depth, /* red */ Y,
                     gamma_table, conv);
               set_value(row, rowbytes, 3*x+1, bit_depth, /* green */
                  (depth_max * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
               set_value(row, rowbytes, 3*x+2, bit_depth, /* blue */
                  (Y * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
            }
         }
         break;

   /* 4 channels: linear combinations of, from the top-left corner clockwise,
    *    transparent, red, green, blue.
    */
      case 4:
         {
            /* x0: the transparent->blue scale (the value of the blue and alpha
             *     components) at the start of the row (red and green are 0).
             * x1: the red->green scale (the value of the red and green
             *     components at the end of the row; blue is 0 and alpha is
             *     depth_max).
             */
            png_uint_32 Y = (depth_max * y * 2 + size_max) / (2 * size_max);
            png_uint_32 x;

            /* Interpolate x/depth_max from start to end:
             *
             *        start    end       difference
             * red:     0   depth_max-Y depth_max-Y
             * green:   0       Y             Y
             * blue:    Y       0            -Y
             * alpha:   Y    depth_max  depth_max-Y
             */
            for (x=0; x<=size_max; ++x)
            {
               set_value(row, rowbytes, 4*x+0, bit_depth, /* red */
                  ((depth_max-Y) * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
               set_value(row, rowbytes, 4*x+1, bit_depth, /* green */
                  (Y * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
               set_value(row, rowbytes, 4*x+2, bit_depth, /* blue */
                  Y - (Y * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
               set_value(row, rowbytes, 4*x+3, bit_depth, /* alpha */
                  Y + ((depth_max-Y) * x * 2 + size_max) / (2 * size_max),
                  gamma_table, conv);
            }
         }
         break;

      default:
         fprintf(stderr, "makepng: internal bad channel count\n");
         exit(2);
   }
}

static int /* 0 on success, else an error code */
write_png(FILE *fp, int color_type, int bit_depth,
   volatile png_fixed_point gamma, chunk_insert * volatile insert)
{
   png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,0,0,0);
   volatile png_infop info_ptr = NULL;
   volatile png_bytep row = NULL;

   if (png_ptr == NULL)
   {
      fprintf(stderr, "makepng: OOM allocating write structure\n");
      return 1;
   }

   if (setjmp(png_jmpbuf(png_ptr)))
   {
      png_structp nv_ptr = png_ptr;
      png_infop nv_info = info_ptr;

      png_ptr = NULL;
      info_ptr = NULL;
      png_destroy_write_struct(&nv_ptr, &nv_info);
      if (row != NULL) free(row);
      return 1;
   }

   png_init_io(png_ptr, fp);

   info_ptr = png_create_info_struct(png_ptr);
   if (info_ptr == NULL)
      png_error(png_ptr, "OOM allocating info structure");

   {
      unsigned int size = image_size_of_type(color_type, bit_depth);
      png_fixed_point real_gamma = 45455; /* For sRGB */
      png_byte gamma_table[256];
      double conv;

      /* This function uses the libpng values used on read to carry extra
       * information about the gamma:
       */
      if (gamma == PNG_GAMMA_MAC_18)
         gamma = 65909;

      else if (gamma > 0 && gamma < 1000)
         gamma = PNG_FP_1;

      if (gamma > 0)
         real_gamma = gamma;

      {
         unsigned int i;

         if (real_gamma == 45455) for (i=0; i<256; ++i)
         {
            gamma_table[i] = (png_byte)i;
            conv = 1.;
         }

         else
         {
            /* Convert 'i' from sRGB (45455) to real_gamma, this makes
             * the images look the same regardless of the gAMA chunk.
             */
            conv = real_gamma;
            conv /= 45455;

            gamma_table[0] = 0;

            for (i=0; i<255; ++i)
               gamma_table[i] = (png_byte)floor(pow(i/255.,conv) * 255 + 127.5);

            gamma_table[255] = 255;
         }
      }

      png_set_IHDR(png_ptr, info_ptr, size, size, bit_depth, color_type,
         PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

      if (color_type & PNG_COLOR_MASK_PALETTE)
      {
         int npalette;
         png_color palette[256];
         png_byte trans[256];

         npalette = generate_palette(palette, trans, bit_depth, gamma_table);
         png_set_PLTE(png_ptr, info_ptr, palette, npalette);
         png_set_tRNS(png_ptr, info_ptr, trans, npalette-1,
            NULL/*transparent color*/);

         /* Reset gamma_table to prevent the image rows being changed */
         for (npalette=0; npalette<256; ++npalette)
            gamma_table[npalette] = (png_byte)npalette;
      }

      if (gamma == PNG_DEFAULT_sRGB)
         png_set_sRGB(png_ptr, info_ptr, PNG_sRGB_INTENT_ABSOLUTE);

      else if (gamma > 0) /* Else don't set color space information */
      {
         png_set_gAMA_fixed(png_ptr, info_ptr, real_gamma);

         /* Just use the sRGB values here. */
         png_set_cHRM_fixed(png_ptr, info_ptr,
            /* color      x       y */
            /* white */ 31270, 32900,
            /* red   */ 64000, 33000,
            /* green */ 30000, 60000,
            /* blue  */ 15000,  6000
         );
      }

      /* Insert extra information. */
      while (insert != NULL)
      {
         insert->insert(png_ptr, info_ptr, insert->nparams, insert->parameters);
         insert = insert->next;
      }

      /* Write the file header. */
      png_write_info(png_ptr, info_ptr);

      /* Restrict the filters */
      png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_NO_FILTERS);

      {
         int passes = png_set_interlace_handling(png_ptr);
         int pass;
         png_size_t rowbytes = png_get_rowbytes(png_ptr, info_ptr);

         row = malloc(rowbytes);

         if (row == NULL)
            png_error(png_ptr, "OOM allocating row buffer");

         for (pass = 0; pass < passes; ++pass)
         {
            unsigned int y;

            for (y=0; y<size; ++y)
            {
               generate_row(row, rowbytes, y, color_type, bit_depth,
                  gamma_table, conv);
               png_write_row(png_ptr, row);
            }
         }
      }
   }

   /* Finish writing the file. */
   png_write_end(png_ptr, info_ptr);

   {
      png_structp nv_ptr = png_ptr;
      png_infop nv_info = info_ptr;

      png_ptr = NULL;
      info_ptr = NULL;
      png_destroy_write_struct(&nv_ptr, &nv_info);
   }
   free(row);
   return 0;
}


static size_t
load_file(png_const_charp name, png_bytepp result)
{
   FILE *fp = tmpfile();

   if (fp != NULL)
   {
      FILE *ip = fopen(name, "rb");

      if (ip != NULL)
      {
         size_t total = 0;
         int ch;

         for (;;)
         {
            ch = getc(ip);
            if (ch == EOF) break;
            putc(ch, fp);
            ++total;
         }

         if (ferror(ip))
         {
            perror(name);
            fprintf(stderr, "%s: read error\n", name);
            (void)fclose(ip);
         }

         else
         {
            (void)fclose(ip);

            if (ferror(fp))
            {
               perror("temporary file");
               fprintf(stderr, "temporary file write error\n");
            }

            else
            {
               rewind(fp);

               if (total > 0)
               {
                  png_bytep data = malloc(total);

                  if (data != NULL)
                  {
                     size_t new_size = 0;

                     for (;;)
                     {
                        ch = getc(fp);
                        if (ch == EOF) break;
                        data[new_size++] = (png_byte)ch;
                     }

                     if (ferror(fp) || new_size != total)
                     {
                        perror("temporary file");
                        fprintf(stderr, "temporary file read error\n");
                        free(data);
                     }

                     else
                     {
                        (void)fclose(fp);
                        *result = data;
                        return total;
                     }
                  }

                  else
                     fprintf(stderr, "%s: out of memory loading file\n", name);
               }

               else
                  fprintf(stderr, "%s: empty file\n", name);
            }
         }
      }

      else
      {
         perror(name);
         fprintf(stderr, "%s: open failed\n", name);
      }

      fclose(fp);
   }

   else
      fprintf(stderr, "makepng: %s: could not open temporary file\n", name);

   exit(1);
   return 0;
}

static png_size_t
load_fake(png_charp param, png_bytepp profile)
{
   char *endptr = NULL;
   unsigned long long int size = strtoull(param, &endptr, 0/*base*/);

   /* The 'fake' format is <number>*[string] */
   if (endptr != NULL && *endptr == '*')
   {
      size_t len = strlen(++endptr);
      size_t result = (size_t)size;

      if (len == 0) len = 1; /* capture the terminating '\0' */

      /* Now repeat that string to fill 'size' bytes. */
      if (result == size && (*profile = malloc(result)) != NULL)
      {
         png_bytep out = *profile;

         if (len == 1)
            memset(out, *endptr, result);

         else
         {
            while (size >= len)
            {
               memcpy(out, endptr, len);
               out += len;
               size -= len;
            }
            memcpy(out, endptr, size);
         }

         return result;
      }

      else
      {
         fprintf(stderr, "%s: size exceeds system limits\n", param);
         exit(1);
      }
   }

   return 0;
}

static void
check_param_count(int nparams, int expect)
{
   if (nparams != expect)
   {
      fprintf(stderr, "bad parameter count (internal error)\n");
      exit(1);
   }
}

static void
insert_iCCP(png_structp png_ptr, png_infop info_ptr, int nparams,
   png_charpp params)
{
   png_bytep profile = NULL;
   png_uint_32 proflen = 0;
   int result;

   check_param_count(nparams, 2);

   switch (params[1][0])
   {
      case '<':
         {
            png_size_t filelen = load_file(params[1]+1, &profile);
            if (filelen > 0xffffffff) /* Maximum profile length */
            {
               fprintf(stderr, "%s: file too long (%lu) for an ICC profile\n",
                  params[1]+1, (unsigned long)filelen);
               exit(1);
            }
            proflen = (png_uint_32)filelen;
         }
         break;

      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
         {
            png_size_t fake_len = load_fake(params[1], &profile);

            if (fake_len > 0) /* else a simple parameter */
            {
               if (fake_len > 0xffffffff) /* Maximum profile length */
               {
                  fprintf(stderr,
                     "%s: fake data too long (%lu) for an ICC profile\n",
                     params[1], (unsigned long)fake_len);
                  exit(1);
               }
               proflen = (png_uint_32)(fake_len & ~3U);
               /* Always fix up the profile length. */
               png_save_uint_32(profile, proflen);
               break;
            }
         }

      default:
         fprintf(stderr, "--insert iCCP \"%s\": unrecognized\n", params[1]);
         fprintf(stderr, "  use '<' to read a file: \"<filename\"\n");
         exit(1);
   }

   result = 1;

   if (proflen & 3)
   {
      fprintf(stderr,
         "--insert iCCP %s: profile length must be a multiple of 4\n",
         params[1]);
      result = 0; /* Cannot fix this! */
   }

   if (profile != NULL && proflen > 3)
   {
      png_uint_32 prof_header = png_get_uint_32(profile);

      if (prof_header != proflen)
      {
         fprintf(stderr, "--insert iCCP %s: profile length field wrong:\n",
            params[1]);
         fprintf(stderr, "  actual %lu, recorded value %lu (corrected)\n",
            (unsigned long)proflen, (unsigned long)prof_header);
         png_save_uint_32(profile, proflen);
      }
   }

   if (result && profile != NULL && proflen >=4)
      png_set_iCCP(png_ptr, info_ptr, params[0], PNG_COMPRESSION_TYPE_BASE,
         profile, proflen);

   if (profile)
      free(profile);

   if (!result)
      exit(1);
}

static void
clear_text(png_text *text, png_charp keyword)
{
   text->compression = -1; /* none */
   text->key = keyword;
   text->text = NULL;
   text->text_length = 0; /* libpng calculates this */
   text->itxt_length = 0; /* libpng calculates this */
   text->lang = NULL;
   text->lang_key = NULL;
}

static void
set_text(png_structp png_ptr, png_infop info_ptr, png_textp text,
   png_charp param)
{
   switch (param[0])
   {
      case '<':
         {
            png_bytep file = NULL;

            text->text_length = load_file(param+1, &file);
            text->text = (png_charp)file;
         }
         break;

      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
         {
            png_bytep data = NULL;
            png_size_t fake_len = load_fake(param, &data);

            if (fake_len > 0) /* else a simple parameter */
            {
               text->text_length = fake_len;
               text->text = (png_charp)data;
               break;
            }
         }

      default:
         text->text = param;
         break;
   }

   png_set_text(png_ptr, info_ptr, text, 1);

   if (text->text != param)
      free(text->text);
}

static void
insert_tEXt(png_structp png_ptr, png_infop info_ptr, int nparams,
   png_charpp params)
{
   png_text text;

   check_param_count(nparams, 2);
   clear_text(&text, params[0]);
   set_text(png_ptr, info_ptr, &text, params[1]);
}

static void
insert_zTXt(png_structp png_ptr, png_infop info_ptr, int nparams,
   png_charpp params)
{
   png_text text;

   check_param_count(nparams, 2);
   clear_text(&text, params[0]);
   text.compression = 0; /* deflate */
   set_text(png_ptr, info_ptr, &text, params[1]);
}

static void
insert_iTXt(png_structp png_ptr, png_infop info_ptr, int nparams,
   png_charpp params)
{
   png_text text;

   check_param_count(nparams, 4);
   clear_text(&text, params[0]);
   text.compression = 2; /* iTXt + deflate */
   text.lang = params[1];/* language tag */
   text.lang_key = params[2]; /* translated keyword */
   set_text(png_ptr, info_ptr, &text, params[3]);
}

static void
insert_hIST(png_structp png_ptr, png_infop info_ptr, int nparams, png_charpp params)
{
   int i;
   png_uint_16 freq[256];

   /* libpng takes the count from the PLTE count; we don't check it here but we
    * do set the array to 0 for unspecified entries.
    */
   memset(freq, 0, sizeof freq);
   for (i=0; i<nparams; ++i)
   {
      char *endptr = NULL;
      unsigned long int l = strtoul(params[i], &endptr, 0/*base*/);

      if (params[i][0] && *endptr == 0 && l <= 65535)
         freq[i] = (png_uint_16)l;

      else
      {
         fprintf(stderr, "hIST[%d]: %s: invalid frequency\n", i, params[i]);
         exit(1);
      }
   }

   png_set_hIST(png_ptr, info_ptr, freq);
}

#if 0
static void
insert_sPLT(png_structp png_ptr, png_infop info_ptr, int nparams, png_charpp params)
{
   fprintf(stderr, "insert sPLT: NYI\n");
}
#endif

static int
find_parameters(png_const_charp what, png_charp param, png_charp *list,
   int nparams)
{
   /* Parameters are separated by '\n' or ':' characters, up to nparams are
    * accepted (more is an error) and the number found is returned.
    */
   int i;
   for (i=0; *param && i<nparams; ++i)
   {
      list[i] = param;
      while (*++param) if (*param == '\n' || *param == ':')
      {
         *param++ = 0; /* Terminate last parameter */
         break;        /* And start a new one. */
      }
   }

   if (*param)
   {
      fprintf(stderr, "--insert %s: too many parameters (%s)\n", what, param);
      exit(1);
   }

   list[i] = NULL; /* terminates list */
   return i; /* number of parameters filled in */
}

static void
bad_parameter_count(png_const_charp what, int nparams)
{
   fprintf(stderr, "--insert %s: bad parameter count %d\n", what, nparams);
   exit(1);
}

static chunk_insert *
make_insert(png_const_charp what,
   void (*insert)(png_structp, png_infop, int, png_charpp),
   int nparams, png_charpp list)
{
   int i;
   chunk_insert *cip;

   cip = malloc(offsetof(chunk_insert,parameters) +
      nparams * sizeof (png_charp));

   if (cip == NULL)
   {
      fprintf(stderr, "--insert %s: out of memory allocating %d parameters\n",
         what, nparams);
      exit(1);
   }

   cip->next = NULL;
   cip->insert = insert;
   cip->nparams = nparams;
   for (i=0; i<nparams; ++i)
      cip->parameters[i] = list[i];

   return cip;
}

static chunk_insert *
find_insert(png_const_charp what, png_charp param)
{
   png_uint_32 chunk = 0;
   png_charp parameter_list[1024];
   int i, nparams;

   /* Assemble the chunk name */
   for (i=0; i<4; ++i)
   {
      char ch = what[i];

      if ((ch >= 65 && ch <= 90) || (ch >= 97 && ch <= 122))
         chunk = (chunk << 8) + what[i];

      else
         break;
   }

   if (i < 4 || what[4] != 0)
   {
      fprintf(stderr, "makepng --insert \"%s\": invalid chunk name\n", what);
      exit(1);
   }

   /* Assemble the parameter list. */
   nparams = find_parameters(what, param, parameter_list, 1024);

#  define CHUNK(a,b,c,d) (((a)<<24)+((b)<<16)+((c)<<8)+(d))

   switch (chunk)
   {
      case CHUNK(105,67,67,80):  /* iCCP */
         if (nparams == 2)
            return make_insert(what, insert_iCCP, nparams, parameter_list);
         break;

      case CHUNK(116,69,88,116): /* tEXt */
         if (nparams == 2)
            return make_insert(what, insert_tEXt, nparams, parameter_list);
         break;

      case CHUNK(122,84,88,116): /* zTXt */
         if (nparams == 2)
            return make_insert(what, insert_zTXt, nparams, parameter_list);
         break;

      case CHUNK(105,84,88,116): /* iTXt */
         if (nparams == 4)
            return make_insert(what, insert_iTXt, nparams, parameter_list);
         break;

      case CHUNK(104,73,83,84):  /* hIST */
         if (nparams <= 256)
            return make_insert(what, insert_hIST, nparams, parameter_list);
         break;

#if 0
      case CHUNK(115,80,76,84):  /* sPLT */
         return make_insert(what, insert_sPLT, nparams, parameter_list);
#endif

      default:
         fprintf(stderr, "makepng --insert \"%s\": unrecognized chunk name\n",
            what);
         exit(1);
   }

   bad_parameter_count(what, nparams);
   return NULL;
}

int
main(int argc, char **argv)
{
   FILE *fp = stdout;
   int color_type = 8; /* invalid */
   int bit_depth = 32; /* invalid */
   png_fixed_point gamma = 0; /* not set */
   chunk_insert *head_insert = NULL;
   chunk_insert **insert_ptr = &head_insert;

   while (--argc > 0)
   {
      const char *arg = *++argv;

      if (strcmp(arg, "--sRGB") == 0)
      {
         gamma = PNG_DEFAULT_sRGB;
         continue;
      }

      if (strcmp(arg, "--linear") == 0)
      {
         gamma = PNG_FP_1;
         continue;
      }

      if (strcmp(arg, "--1.8") == 0)
      {
         gamma = PNG_GAMMA_MAC_18;
         continue;
      }

      if (argc >= 3 && strcmp(arg, "--insert") == 0)
      {
         png_const_charp what = *++argv;
         png_charp param = *++argv;
         chunk_insert *new_insert;

         argc -= 2;

         new_insert = find_insert(what, param);

         if (new_insert != NULL)
         {
            *insert_ptr = new_insert;
            insert_ptr = &new_insert->next;
         }

         continue;
      }

      if (arg[0] == '-')
      {
         fprintf(stderr, "makepng: %s: invalid option\n", arg);
         exit(1);
      }

      if (strcmp(arg, "palette") == 0)
      {
         color_type = PNG_COLOR_TYPE_PALETTE;
         continue;
      }

      if (strncmp(arg, "gray", 4) == 0)
      {
         if (arg[5] == 0)
         {
            color_type = PNG_COLOR_TYPE_GRAY;
            continue;
         }

         else if (strcmp(arg+4, "a") == 0 ||
            strcmp(arg+4, "alpha") == 0 ||
            strcmp(arg+4, "-alpha") == 0)
         {
            color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
            continue;
         }
      }

      if (strncmp(arg, "rgb", 3) == 0)
      {
         if (arg[4] == 0)
         {
            color_type = PNG_COLOR_TYPE_RGB;
            continue;
         }

         else if (strcmp(arg+3, "a") == 0 ||
            strcmp(arg+3, "alpha") == 0 ||
            strcmp(arg+3, "-alpha") == 0)
         {
            color_type = PNG_COLOR_TYPE_RGB_ALPHA;
            continue;
         }
      }

      if (color_type == 8)
      {
         color_type = atoi(arg);
         if (color_type < 0 || color_type > 6 || color_type == 1 ||
            color_type == 5)
         {
            fprintf(stderr, "makepng: %s: not a valid color type\n", arg);
            exit(1);
         }

         continue;
      }

      if (bit_depth == 32)
      {
         bit_depth = atoi(arg);
         if (bit_depth <= 0 || bit_depth > 16 ||
            (bit_depth & -bit_depth) != bit_depth)
         {
            fprintf(stderr, "makepng: %s: not a valid bit depth\n", arg);
            exit(1);
         }

         continue;
      }

      if (argc == 1) /* It's the file name */
      {
         fp = fopen(arg, "wb");
         if (fp == NULL)
         {
            fprintf(stderr, "%s: %s: could not open\n", arg, strerror(errno));
            exit(1);
         }

         continue;
      }

      fprintf(stderr, "makepng: %s: unknown argument\n", arg);
      exit(1);
   } /* argument while loop */

   if (color_type == 8 || bit_depth == 32)
   {
      fprintf(stderr, "usage: makepng [--sRGB|--linear|--1.8] "
         "color-type bit-depth [file-name]\n"
         "  Make a test PNG file, by default writes to stdout.\n");
      exit(1);
   }

   return write_png(fp, color_type, bit_depth, gamma, head_insert);
}