libpng: update to 1.2.43

third_party/libpng/pngrtran.c

 
 /* pngrtran.c - transforms the data in a row for PNG readers
  *
- * Last changed in libpng 1.2.37 [June 4, 2009]
- * For conditions of distribution and use, see copyright notice in png.h
- * Copyright (c) 1998-2009 Glenn Randers-Pehrson
+ * Last changed in libpng 1.2.43 [February 25, 2010]
+ * Copyright (c) 1998-2010 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ *
  * This file contains functions optionally called by an application
  * in order to tell libpng how to handle data when reading a PNG.
  * Transformations that are used in both reading and writing are
  * in pngtrans.c.
  */
 
 #define PNG_INTERNAL
+#define PNG_NO_PEDANTIC_WARNINGS
 #include "png.h"
-#if defined(PNG_READ_SUPPORTED)
+#ifdef PNG_READ_SUPPORTED
 
 /* Set the action on getting a CRC error for an ancillary or critical chunk. */
 void PNGAPI
 png_set_crc_action(png_structp png_ptr, int crit_action, int ancil_action)
 {
    png_debug(1, "in png_set_crc_action");
-   /* Tell libpng how we react to CRC errors in critical chunks */
+ 
    if (png_ptr == NULL)
       return;
+
+   /* Tell libpng how we react to CRC errors in critical chunks */
    switch (crit_action)
    {
       case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
          break;
 
       case PNG_CRC_WARN_USE:                               /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
          break;
 
       case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                            PNG_FLAG_CRC_CRITICAL_IGNORE;
          break;
 
       case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
          png_warning(png_ptr,
             "Can't discard critical data on CRC error.");
       case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
 
       case PNG_CRC_DEFAULT:
       default:
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          break;
    }
 
+   /* Tell libpng how we react to CRC errors in ancillary chunks */
    switch (ancil_action)
    {
       case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
          break;
 
       case PNG_CRC_WARN_USE:                              /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
          break;
 
@@ skipping 19 matching lines @@
 
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
     defined(PNG_FLOATING_POINT_SUPPORTED)
 /* Handle alpha and tRNS via a background color */
 void PNGAPI
 png_set_background(png_structp png_ptr,
    png_color_16p background_color, int background_gamma_code,
    int need_expand, double background_gamma)
 {
    png_debug(1, "in png_set_background");
+ 
    if (png_ptr == NULL)
       return;
    if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
    {
       png_warning(png_ptr, "Application must supply a known background gamma");
       return;
    }
 
    png_ptr->transformations |= PNG_BACKGROUND;
    png_memcpy(&(png_ptr->background), background_color,
       png_sizeof(png_color_16));
    png_ptr->background_gamma = (float)background_gamma;
    png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
    png_ptr->transformations |= (need_expand ? PNG_BACKGROUND_EXPAND : 0);
 }
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
+#ifdef PNG_READ_16_TO_8_SUPPORTED
 /* Strip 16 bit depth files to 8 bit depth */
 void PNGAPI
 png_set_strip_16(png_structp png_ptr)
 {
    png_debug(1, "in png_set_strip_16");
+
    if (png_ptr == NULL)
       return;
    png_ptr->transformations |= PNG_16_TO_8;
 }
 #endif
 
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
 void PNGAPI
 png_set_strip_alpha(png_structp png_ptr)
 {
    png_debug(1, "in png_set_strip_alpha");
+
    if (png_ptr == NULL)
       return;
    png_ptr->flags |= PNG_FLAG_STRIP_ALPHA;
 }
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
+#ifdef PNG_READ_DITHER_SUPPORTED
 /* Dither file to 8 bit.  Supply a palette, the current number
  * of elements in the palette, the maximum number of elements
  * allowed, and a histogram if possible.  If the current number
  * of colors is greater then the maximum number, the palette will be
  * modified to fit in the maximum number.  "full_dither" indicates
  * whether we need a dithering cube set up for RGB images, or if we
  * simply are reducing the number of colors in a paletted image.
  */
 
 typedef struct png_dsort_struct
 {
    struct png_dsort_struct FAR * next;
    png_byte left;
    png_byte right;
 } png_dsort;
 typedef png_dsort FAR *       png_dsortp;
 typedef png_dsort FAR * FAR * png_dsortpp;
 
 void PNGAPI
 png_set_dither(png_structp png_ptr, png_colorp palette,
    int num_palette, int maximum_colors, png_uint_16p histogram,
    int full_dither)
 {
    png_debug(1, "in png_set_dither");
+
    if (png_ptr == NULL)
       return;
    png_ptr->transformations |= PNG_DITHER;
 
    if (!full_dither)
    {
       int i;
 
       png_ptr->dither_index = (png_bytep)png_malloc(png_ptr,
          (png_uint_32)(num_palette * png_sizeof(png_byte)));
@@ skipping 149 matching lines @@
          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
             (png_uint_32)(num_palette * png_sizeof(png_byte)));
 
          /* Initialize the sort array */
          for (i = 0; i < num_palette; i++)
          {
             png_ptr->index_to_palette[i] = (png_byte)i;
             png_ptr->palette_to_index[i] = (png_byte)i;
          }
 
-         hash = (png_dsortpp)png_malloc(png_ptr, (png_uint_32)(769 *
+         hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
             png_sizeof(png_dsortp)));
-         png_memset(hash, 0, 769 * png_sizeof(png_dsortp));
 
          num_new_palette = num_palette;
 
          /* Initial wild guess at how far apart the farthest pixel
           * pair we will be eliminating will be.  Larger
           * numbers mean more areas will be allocated, Smaller
           * numbers run the risk of not saving enough data, and
           * having to do this all over again.
           *
           * I have not done extensive checking on this number.
@@ skipping 74 matching lines @@
                                  png_ptr->dither_index[k] =
                                     png_ptr->index_to_palette[j];
                            }
                         }
 
                         png_ptr->index_to_palette[png_ptr->palette_to_index
                            [num_new_palette]] = png_ptr->index_to_palette[j];
                         png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
                            = png_ptr->palette_to_index[num_new_palette];
 
-                        png_ptr->index_to_palette[j] = (png_byte)num_new_palette;
-                        png_ptr->palette_to_index[num_new_palette] = (png_byte)j;
+                        png_ptr->index_to_palette[j] =
+                            (png_byte)num_new_palette;
+                        png_ptr->palette_to_index[num_new_palette] =
+                            (png_byte)j;
                      }
                      if (num_new_palette <= maximum_colors)
                         break;
                   }
                   if (num_new_palette <= maximum_colors)
                      break;
                }
             }
 
             for (i = 0; i < 769; i++)
@@ skipping 29 matching lines @@
    if (full_dither)
    {
       int i;
       png_bytep distance;
       int total_bits = PNG_DITHER_RED_BITS + PNG_DITHER_GREEN_BITS +
          PNG_DITHER_BLUE_BITS;
       int num_red = (1 << PNG_DITHER_RED_BITS);
       int num_green = (1 << PNG_DITHER_GREEN_BITS);
       int num_blue = (1 << PNG_DITHER_BLUE_BITS);
       png_size_t num_entries = ((png_size_t)1 << total_bits);
-      png_ptr->palette_lookup = (png_bytep )png_malloc(png_ptr,
+
+      png_ptr->palette_lookup = (png_bytep )png_calloc(png_ptr,
          (png_uint_32)(num_entries * png_sizeof(png_byte)));
-      png_memset(png_ptr->palette_lookup, 0, num_entries *
-         png_sizeof(png_byte));
 
       distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
          png_sizeof(png_byte)));
-
       png_memset(distance, 0xff, num_entries * png_sizeof(png_byte));
 
       for (i = 0; i < num_palette; i++)
       {
          int ir, ig, ib;
          int r = (palette[i].red >> (8 - PNG_DITHER_RED_BITS));
          int g = (palette[i].green >> (8 - PNG_DITHER_GREEN_BITS));
          int b = (palette[i].blue >> (8 - PNG_DITHER_BLUE_BITS));
 
          for (ir = 0; ir < num_red; ir++)
          {
             /* int dr = abs(ir - r); */
             int dr = ((ir > r) ? ir - r : r - ir);
-            int index_r = (ir << (PNG_DITHER_BLUE_BITS + PNG_DITHER_GREEN_BITS));
+            int index_r = (ir << (PNG_DITHER_BLUE_BITS +
+                PNG_DITHER_GREEN_BITS));
 
             for (ig = 0; ig < num_green; ig++)
             {
                /* int dg = abs(ig - g); */
                int dg = ((ig > g) ? ig - g : g - ig);
                int dt = dr + dg;
                int dm = ((dr > dg) ? dr : dg);
                int index_g = index_r | (ig << PNG_DITHER_BLUE_BITS);
 
                for (ib = 0; ib < num_blue; ib++)
@@ skipping 26 matching lines @@
  * also needlessly introduces small errors.
  *
  * We will turn off gamma transformation later if no semitransparent entries
  * are present in the tRNS array for palette images.  We can't do it here
  * because we don't necessarily have the tRNS chunk yet.
  */
 void PNGAPI
 png_set_gamma(png_structp png_ptr, double scrn_gamma, double file_gamma)
 {
    png_debug(1, "in png_set_gamma");
+
    if (png_ptr == NULL)
       return;
+
    if ((fabs(scrn_gamma * file_gamma - 1.0) > PNG_GAMMA_THRESHOLD) ||
        (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) ||
        (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
      png_ptr->transformations |= PNG_GAMMA;
    png_ptr->gamma = (float)file_gamma;
    png_ptr->screen_gamma = (float)scrn_gamma;
 }
 #endif
 
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expand paletted images to RGB, expand grayscale images of
  * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
  * to alpha channels.
  */
 void PNGAPI
 png_set_expand(png_structp png_ptr)
 {
    png_debug(1, "in png_set_expand");
+
    if (png_ptr == NULL)
       return;
+
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 
 /* GRR 19990627:  the following three functions currently are identical
  *  to png_set_expand().  However, it is entirely reasonable that someone
  *  might wish to expand an indexed image to RGB but *not* expand a single,
  *  fully transparent palette entry to a full alpha channel--perhaps instead
  *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
  *  the transparent color with a particular RGB value, or drop tRNS entirely.
  *  IOW, a future version of the library may make the transformations flag
  *  a bit more fine-grained, with separate bits for each of these three
  *  functions.
  *
  *  More to the point, these functions make it obvious what libpng will be
  *  doing, whereas "expand" can (and does) mean any number of things.
  *
- *  GRP 20060307: In libpng-1.4.0, png_set_gray_1_2_4_to_8() was modified
- *  to expand only the sample depth but not to expand the tRNS to alpha.
+ *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
+ *  to expand only the sample depth but not to expand the tRNS to alpha
+ *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
  */
 
 /* Expand paletted images to RGB. */
 void PNGAPI
 png_set_palette_to_rgb(png_structp png_ptr)
 {
    png_debug(1, "in png_set_palette_to_rgb");
+
    if (png_ptr == NULL)
       return;
+
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 
-#if !defined(PNG_1_0_X)
+#ifndef PNG_1_0_X
 /* Expand grayscale images of less than 8-bit depth to 8 bits. */
 void PNGAPI
 png_set_expand_gray_1_2_4_to_8(png_structp png_ptr)
 {
    png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
+
    if (png_ptr == NULL)
       return;
+
    png_ptr->transformations |= PNG_EXPAND;
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 #endif
 
 #if defined(PNG_1_0_X) || defined(PNG_1_2_X)
 /* Expand grayscale images of less than 8-bit depth to 8 bits. */
 /* Deprecated as of libpng-1.2.9 */
 void PNGAPI
 png_set_gray_1_2_4_to_8(png_structp png_ptr)
 {
    png_debug(1, "in png_set_gray_1_2_4_to_8");
+
    if (png_ptr == NULL)
       return;
+
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 }
 #endif
 
 
 /* Expand tRNS chunks to alpha channels. */
 void PNGAPI
 png_set_tRNS_to_alpha(png_structp png_ptr)
 {
    png_debug(1, "in png_set_tRNS_to_alpha");
+
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 void PNGAPI
 png_set_gray_to_rgb(png_structp png_ptr)
 {
    png_debug(1, "in png_set_gray_to_rgb");
+
    png_ptr->transformations |= PNG_GRAY_TO_RGB;
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-#if defined(PNG_FLOATING_POINT_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+#ifdef PNG_FLOATING_POINT_SUPPORTED
 /* Convert a RGB image to a grayscale of the same width.  This allows us,
  * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
  */
 
 void PNGAPI
 png_set_rgb_to_gray(png_structp png_ptr, int error_action, double red,
    double green)
 {
    int red_fixed = (int)((float)red*100000.0 + 0.5);
    int green_fixed = (int)((float)green*100000.0 + 0.5);
    if (png_ptr == NULL)
       return;
    png_set_rgb_to_gray_fixed(png_ptr, error_action, red_fixed, green_fixed);
 }
 #endif
 
 void PNGAPI
 png_set_rgb_to_gray_fixed(png_structp png_ptr, int error_action,
    png_fixed_point red, png_fixed_point green)
 {
    png_debug(1, "in png_set_rgb_to_gray");
+
    if (png_ptr == NULL)
       return;
+
    switch(error_action)
    {
       case 1: png_ptr->transformations |= PNG_RGB_TO_GRAY;
               break;
 
       case 2: png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
               break;
 
       case 3: png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
    }
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_EXPAND_SUPPORTED
       png_ptr->transformations |= PNG_EXPAND;
 #else
    {
       png_warning(png_ptr,
         "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED.");
       png_ptr->transformations &= ~PNG_RGB_TO_GRAY;
    }
 #endif
    {
       png_uint_16 red_int, green_int;
@@ skipping 15 matching lines @@
       }
       png_ptr->rgb_to_gray_red_coeff   = red_int;
       png_ptr->rgb_to_gray_green_coeff = green_int;
       png_ptr->rgb_to_gray_blue_coeff  =
          (png_uint_16)(32768 - red_int - green_int);
    }
 }
 #endif
 
 #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
-    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED) || \
-    defined(PNG_LEGACY_SUPPORTED)
+    defined(PNG_LEGACY_SUPPORTED) || \
+    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
 void PNGAPI
 png_set_read_user_transform_fn(png_structp png_ptr, png_user_transform_ptr
    read_user_transform_fn)
 {
    png_debug(1, "in png_set_read_user_transform_fn");
+
    if (png_ptr == NULL)
       return;
-#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
+
+#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    png_ptr->transformations |= PNG_USER_TRANSFORM;
    png_ptr->read_user_transform_fn = read_user_transform_fn;
 #endif
 #ifdef PNG_LEGACY_SUPPORTED
    if (read_user_transform_fn)
       png_warning(png_ptr,
         "This version of libpng does not support user transforms");
 #endif
 }
 #endif
 
 /* Initialize everything needed for the read.  This includes modifying
  * the palette.
  */
 void /* PRIVATE */
 png_init_read_transformations(png_structp png_ptr)
 {
    png_debug(1, "in png_init_read_transformations");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (png_ptr != NULL)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
+  if (png_ptr != NULL)
 #endif
   {
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) || defined(PNG_READ_SHIFT_SUPPORTED) \
- || defined(PNG_READ_GAMMA_SUPPORTED)
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+    defined(PNG_READ_SHIFT_SUPPORTED) || \
+    defined(PNG_READ_GAMMA_SUPPORTED)
    int color_type = png_ptr->color_type;
 #endif
 
 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* Detect gray background and attempt to enable optimization
     * for gray --> RGB case
     *
     * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
     * RGB_ALPHA (in which case need_expand is superfluous anyway), the
     * background color might actually be gray yet not be flagged as such.
     * This is not a problem for the current code, which uses
     * PNG_BACKGROUND_IS_GRAY only to decide when to do the
     * png_do_gray_to_rgb() transformation.
     */
@@ skipping 66 matching lines @@
       }
       else if (color_type == PNG_COLOR_TYPE_PALETTE)
       {
          png_ptr->background.red   =
             png_ptr->palette[png_ptr->background.index].red;
          png_ptr->background.green =
             png_ptr->palette[png_ptr->background.index].green;
          png_ptr->background.blue  =
             png_ptr->palette[png_ptr->background.index].blue;
 
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
         if (png_ptr->transformations & PNG_INVERT_ALPHA)
         {
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_EXPAND_SUPPORTED
            if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
 #endif
            {
            /* Invert the alpha channel (in tRNS) unless the pixels are
             * going to be expanded, in which case leave it for later
             */
               int i, istop;
               istop=(int)png_ptr->num_trans;
               for (i=0; i<istop; i++)
                  png_ptr->trans[i] = (png_byte)(255 - png_ptr->trans[i]);
@@ skipping 22 matching lines @@
         k=1; /* Partial transparency is present */
     }
     if (k == 0)
       png_ptr->transformations &= ~PNG_GAMMA;
    }
 
    if ((png_ptr->transformations & (PNG_GAMMA | PNG_RGB_TO_GRAY)) &&
         png_ptr->gamma != 0.0)
    {
       png_build_gamma_table(png_ptr);
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
       if (png_ptr->transformations & PNG_BACKGROUND)
       {
          if (color_type == PNG_COLOR_TYPE_PALETTE)
          {
            /* Could skip if no transparency */
             png_color back, back_1;
             png_colorp palette = png_ptr->palette;
             int num_palette = png_ptr->num_palette;
             int i;
             if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
@@ skipping 36 matching lines @@
                {
                   back.red   = (png_byte)png_ptr->background.red;
                   back.green = (png_byte)png_ptr->background.green;
                   back.blue  = (png_byte)png_ptr->background.blue;
                }
                else
                {
                   back.red = (png_byte)(pow(
                      (double)png_ptr->background.red/255, gs) * 255.0 + .5);
                   back.green = (png_byte)(pow(
-                     (double)png_ptr->background.green/255, gs) * 255.0 + .5);
+                     (double)png_ptr->background.green/255, gs) * 255.0
+                         + .5);
                   back.blue = (png_byte)(pow(
                      (double)png_ptr->background.blue/255, gs) * 255.0 + .5);
                }
 
                back_1.red = (png_byte)(pow(
                   (double)png_ptr->background.red/255, g) * 255.0 + .5);
                back_1.green = (png_byte)(pow(
                   (double)png_ptr->background.green/255, g) * 255.0 + .5);
                back_1.blue = (png_byte)(pow(
                   (double)png_ptr->background.blue/255, g) * 255.0 + .5);
@@ skipping 23 matching lines @@
                      palette[i].blue = png_ptr->gamma_from_1[w];
                   }
                }
                else
                {
                   palette[i].red = png_ptr->gamma_table[palette[i].red];
                   palette[i].green = png_ptr->gamma_table[palette[i].green];
                   palette[i].blue = png_ptr->gamma_table[palette[i].blue];
                }
             }
-            /* Prevent the transformations being done again, and make sure
-             * that the now spurious alpha channel is stripped - the code
-             * has just reduced background composition and gamma correction
-             * to a simple alpha channel strip.
-             */
-            png_ptr->transformations &= ~PNG_BACKGROUND;
-            png_ptr->transformations &= ~PNG_GAMMA;
-            png_ptr->transformations |= PNG_STRIP_ALPHA;
+            /* Prevent the transformations being done again, and make sure
+             * that the now spurious alpha channel is stripped - the code
+             * has just reduced background composition and gamma correction
+             * to a simple alpha channel strip.
+             */
+            png_ptr->transformations &= ~PNG_BACKGROUND;
+            png_ptr->transformations &= ~PNG_GAMMA;
+            png_ptr->transformations |= PNG_STRIP_ALPHA;
          }
          /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
          else
          /* color_type != PNG_COLOR_TYPE_PALETTE */
          {
             double m = (double)(((png_uint_32)1 << png_ptr->bit_depth) - 1);
             double g = 1.0;
             double gs = 1.0;
 
             switch (png_ptr->background_gamma_type)
@@ skipping 57 matching lines @@
          int num_palette = png_ptr->num_palette;
          int i;
 
          for (i = 0; i < num_palette; i++)
          {
             palette[i].red = png_ptr->gamma_table[palette[i].red];
             palette[i].green = png_ptr->gamma_table[palette[i].green];
             palette[i].blue = png_ptr->gamma_table[palette[i].blue];
          }
 
-         /* Done the gamma correction. */
-         png_ptr->transformations &= ~PNG_GAMMA;
+         /* Done the gamma correction. */
+         png_ptr->transformations &= ~PNG_GAMMA;
       }
    }
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    else
 #endif
 #endif /* PNG_READ_GAMMA_SUPPORTED && PNG_FLOATING_POINT_SUPPORTED */
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    /* No GAMMA transformation */
    if ((png_ptr->transformations & PNG_BACKGROUND) &&
        (color_type == PNG_COLOR_TYPE_PALETTE))
    {
       int i;
       int istop = (int)png_ptr->num_trans;
       png_color back;
       png_colorp palette = png_ptr->palette;
 
       back.red   = (png_byte)png_ptr->background.red;
@@ skipping 17 matching lines @@
                png_ptr->trans[i], back.blue);
          }
       }
 
       /* Handled alpha, still need to strip the channel. */
       png_ptr->transformations &= ~PNG_BACKGROUND;
       png_ptr->transformations |= PNG_STRIP_ALPHA;
    }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED */
 
-#if defined(PNG_READ_SHIFT_SUPPORTED)
+#ifdef PNG_READ_SHIFT_SUPPORTED
    if ((png_ptr->transformations & PNG_SHIFT) &&
       (color_type == PNG_COLOR_TYPE_PALETTE))
    {
       png_uint_16 i;
       png_uint_16 istop = png_ptr->num_palette;
       int sr = 8 - png_ptr->sig_bit.red;
       int sg = 8 - png_ptr->sig_bit.green;
       int sb = 8 - png_ptr->sig_bit.blue;
 
       if (sr < 0 || sr > 8)
@@ skipping 19 matching lines @@
 }
 
 /* Modify the info structure to reflect the transformations.  The
  * info should be updated so a PNG file could be written with it,
  * assuming the transformations result in valid PNG data.
  */
 void /* PRIVATE */
 png_read_transform_info(png_structp png_ptr, png_infop info_ptr)
 {
    png_debug(1, "in png_read_transform_info");
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+
+#ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          if (png_ptr->num_trans &&
               (png_ptr->transformations & PNG_EXPAND_tRNS))
             info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          else
             info_ptr->color_type = PNG_COLOR_TYPE_RGB;
          info_ptr->bit_depth = 8;
          info_ptr->num_trans = 0;
       }
       else
       {
          if (png_ptr->num_trans)
          {
             if (png_ptr->transformations & PNG_EXPAND_tRNS)
               info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
-#if 0 /* Removed from libpng-1.2.27 */
-            else
-              info_ptr->color_type |= PNG_COLOR_MASK_COLOR;
-#endif
          }
          if (info_ptr->bit_depth < 8)
             info_ptr->bit_depth = 8;
          info_ptr->num_trans = 0;
       }
    }
 #endif
 
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    if (png_ptr->transformations & PNG_BACKGROUND)
    {
       info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
       info_ptr->num_trans = 0;
       info_ptr->background = png_ptr->background;
    }
 #endif
 
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
    if (png_ptr->transformations & PNG_GAMMA)
    {
 #ifdef PNG_FLOATING_POINT_SUPPORTED
       info_ptr->gamma = png_ptr->gamma;
 #endif
 #ifdef PNG_FIXED_POINT_SUPPORTED
       info_ptr->int_gamma = png_ptr->int_gamma;
 #endif
    }
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
+#ifdef PNG_READ_16_TO_8_SUPPORTED
    if ((png_ptr->transformations & PNG_16_TO_8) && (info_ptr->bit_depth == 16))
       info_ptr->bit_depth = 8;
 #endif
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    if (png_ptr->transformations & PNG_GRAY_TO_RGB)
       info_ptr->color_type |= PNG_COLOR_MASK_COLOR;
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
       info_ptr->color_type &= ~PNG_COLOR_MASK_COLOR;
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
+#ifdef PNG_READ_DITHER_SUPPORTED
    if (png_ptr->transformations & PNG_DITHER)
    {
       if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
           (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
           png_ptr->palette_lookup && info_ptr->bit_depth == 8)
       {
          info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
       }
    }
 #endif
 
-#if defined(PNG_READ_PACK_SUPPORTED)
+#ifdef PNG_READ_PACK_SUPPORTED
    if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
       info_ptr->bit_depth = 8;
 #endif
 
    if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       info_ptr->channels = 1;
    else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
       info_ptr->channels = 3;
    else
       info_ptr->channels = 1;
 
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if (png_ptr->flags & PNG_FLAG_STRIP_ALPHA)
       info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
 #endif
 
    if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
       info_ptr->channels++;
 
-#if defined(PNG_READ_FILLER_SUPPORTED)
+#ifdef PNG_READ_FILLER_SUPPORTED
    /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
    if ((png_ptr->transformations & PNG_FILLER) &&
        ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
        (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
    {
       info_ptr->channels++;
       /* If adding a true alpha channel not just filler */
-#if !defined(PNG_1_0_X)
+#ifndef PNG_1_0_X
       if (png_ptr->transformations & PNG_ADD_ALPHA)
         info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
 #endif
    }
 #endif
 
 #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
 defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
      {
        if (info_ptr->bit_depth < png_ptr->user_transform_depth)
          info_ptr->bit_depth = png_ptr->user_transform_depth;
        if (info_ptr->channels < png_ptr->user_transform_channels)
          info_ptr->channels = png_ptr->user_transform_channels;
      }
 #endif
 
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
       info_ptr->bit_depth);
 
    info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
 
-#if !defined(PNG_READ_EXPAND_SUPPORTED)
+#ifndef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr)
       return;
 #endif
 }
 
 /* Transform the row.  The order of transformations is significant,
  * and is very touchy.  If you add a transformation, take care to
  * decide how it fits in with the other transformations here.
  */
 void /* PRIVATE */
 png_do_read_transformations(png_structp png_ptr)
 {
    png_debug(1, "in png_do_read_transformations");
+
    if (png_ptr->row_buf == NULL)
    {
-#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
+#if defined(PNG_STDIO_SUPPORTED) && !defined(_WIN32_WCE)
       char msg[50];
 
       png_snprintf2(msg, 50,
          "NULL row buffer for row %ld, pass %d", (long)png_ptr->row_number,
          png_ptr->pass);
       png_error(png_ptr, msg);
 #else
       png_error(png_ptr, "NULL row buffer");
 #endif
    }
 #ifdef PNG_WARN_UNINITIALIZED_ROW
    if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
       /* Application has failed to call either png_read_start_image()
        * or png_read_update_info() after setting transforms that expand
        * pixels.  This check added to libpng-1.2.19
        */
 #if (PNG_WARN_UNINITIALIZED_ROW==1)
       png_error(png_ptr, "Uninitialized row");
 #else
       png_warning(png_ptr, "Uninitialized row");
 #endif
 #endif
 
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
       if (png_ptr->row_info.color_type == PNG_COLOR_TYPE_PALETTE)
       {
          png_do_expand_palette(&(png_ptr->row_info), png_ptr->row_buf + 1,
             png_ptr->palette, png_ptr->trans, png_ptr->num_trans);
       }
       else
       {
          if (png_ptr->num_trans &&
              (png_ptr->transformations & PNG_EXPAND_tRNS))
             png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
                &(png_ptr->trans_values));
          else
             png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
                NULL);
       }
    }
 #endif
 
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if (png_ptr->flags & PNG_FLAG_STRIP_ALPHA)
       png_do_strip_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
          PNG_FLAG_FILLER_AFTER | (png_ptr->flags & PNG_FLAG_STRIP_ALPHA));
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
    {
       int rgb_error =
-         png_do_rgb_to_gray(png_ptr, &(png_ptr->row_info), png_ptr->row_buf + 1);
+         png_do_rgb_to_gray(png_ptr, &(png_ptr->row_info),
+             png_ptr->row_buf + 1);
       if (rgb_error)
       {
          png_ptr->rgb_to_gray_status=1;
          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
              PNG_RGB_TO_GRAY_WARN)
             png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
              PNG_RGB_TO_GRAY_ERR)
             png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
       }
    }
 #endif
 
 /* From Andreas Dilger e-mail to png-implement, 26 March 1998:
- * 
+ *
  *   In most cases, the "simple transparency" should be done prior to doing
  *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
  *   pixel is transparent.  You would also need to make sure that the
  *   transparency information is upgraded to RGB.
- * 
+ *
  *   To summarize, the current flow is:
  *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
  *                                   with background "in place" if transparent,
  *                                   convert to RGB if necessary
  *   - Gray + alpha -> composite with gray background and remove alpha bytes,
  *                                   convert to RGB if necessary
  *
  *   To support RGB backgrounds for gray images we need:
  *   - Gray + simple transparency -> convert to RGB + simple transparency,
  *                                   compare 3 or 6 bytes and composite with
  *                                   background "in place" if transparent
  *                                   (3x compare/pixel compared to doing
  *                                   composite with gray bkgrnd)
  *   - Gray + alpha -> convert to RGB + alpha, composite with background and
  *                                   remove alpha bytes (3x float
  *                                   operations/pixel compared with composite
  *                                   on gray background)
  *
  *  Greg's change will do this.  The reason it wasn't done before is for
  *  performance, as this increases the per-pixel operations.  If we would check
  *  in advance if the background was gray or RGB, and position the gray-to-RGB
  *  transform appropriately, then it would save a lot of work/time.
  */
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* If gray -> RGB, do so now only if background is non-gray; else do later
     * for performance reasons
     */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
       png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    if ((png_ptr->transformations & PNG_BACKGROUND) &&
       ((png_ptr->num_trans != 0 ) ||
       (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)))
       png_do_background(&(png_ptr->row_info), png_ptr->row_buf + 1,
          &(png_ptr->trans_values), &(png_ptr->background)
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
          , &(png_ptr->background_1),
          png_ptr->gamma_table, png_ptr->gamma_from_1,
          png_ptr->gamma_to_1, png_ptr->gamma_16_table,
          png_ptr->gamma_16_from_1, png_ptr->gamma_16_to_1,
          png_ptr->gamma_shift
 #endif
 );
 #endif
 
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
    if ((png_ptr->transformations & PNG_GAMMA) &&
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
        !((png_ptr->transformations & PNG_BACKGROUND) &&
        ((png_ptr->num_trans != 0) ||
        (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
 #endif
        (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
       png_do_gamma(&(png_ptr->row_info), png_ptr->row_buf + 1,
           png_ptr->gamma_table, png_ptr->gamma_16_table,
           png_ptr->gamma_shift);
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
+#ifdef PNG_READ_16_TO_8_SUPPORTED
    if (png_ptr->transformations & PNG_16_TO_8)
       png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
+#ifdef PNG_READ_DITHER_SUPPORTED
    if (png_ptr->transformations & PNG_DITHER)
    {
       png_do_dither((png_row_infop)&(png_ptr->row_info), png_ptr->row_buf + 1,
          png_ptr->palette_lookup, png_ptr->dither_index);
       if (png_ptr->row_info.rowbytes == (png_uint_32)0)
          png_error(png_ptr, "png_do_dither returned rowbytes=0");
    }
 #endif
 
-#if defined(PNG_READ_INVERT_SUPPORTED)
+#ifdef PNG_READ_INVERT_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_MONO)
       png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_SHIFT_SUPPORTED)
+#ifdef PNG_READ_SHIFT_SUPPORTED
    if (png_ptr->transformations & PNG_SHIFT)
       png_do_unshift(&(png_ptr->row_info), png_ptr->row_buf + 1,
          &(png_ptr->shift));
 #endif
 
-#if defined(PNG_READ_PACK_SUPPORTED)
+#ifdef PNG_READ_PACK_SUPPORTED
    if (png_ptr->transformations & PNG_PACK)
       png_do_unpack(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_BGR_SUPPORTED)
+#ifdef PNG_READ_BGR_SUPPORTED
    if (png_ptr->transformations & PNG_BGR)
       png_do_bgr(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_PACKSWAP_SUPPORTED)
+#ifdef PNG_READ_PACKSWAP_SUPPORTED
    if (png_ptr->transformations & PNG_PACKSWAP)
       png_do_packswap(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* If gray -> RGB, do so now only if we did not do so above */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
       png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_FILLER_SUPPORTED)
+#ifdef PNG_READ_FILLER_SUPPORTED
    if (png_ptr->transformations & PNG_FILLER)
       png_do_read_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
          (png_uint_32)png_ptr->filler, png_ptr->flags);
 #endif
 
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_ALPHA)
       png_do_read_invert_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_ALPHA)
       png_do_read_swap_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_SWAP_SUPPORTED)
+#ifdef PNG_READ_SWAP_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_BYTES)
       png_do_swap(&(png_ptr->row_info), png_ptr->row_buf + 1);
 #endif
 
-#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
+#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
     {
       if (png_ptr->read_user_transform_fn != NULL)
          (*(png_ptr->read_user_transform_fn)) /* User read transform function */
             (png_ptr,                    /* png_ptr */
                &(png_ptr->row_info),     /* row_info: */
                /*  png_uint_32 width;       width of row */
                /*  png_uint_32 rowbytes;    number of bytes in row */
                /*  png_byte color_type;     color type of pixels */
                /*  png_byte bit_depth;      bit depth of samples */
                /*  png_byte channels;       number of channels (1-4) */
                /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
                png_ptr->row_buf + 1);    /* start of pixel data for row */
-#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
+#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
       if (png_ptr->user_transform_depth)
          png_ptr->row_info.bit_depth = png_ptr->user_transform_depth;
       if (png_ptr->user_transform_channels)
          png_ptr->row_info.channels = png_ptr->user_transform_channels;
 #endif
       png_ptr->row_info.pixel_depth = (png_byte)(png_ptr->row_info.bit_depth *
          png_ptr->row_info.channels);
       png_ptr->row_info.rowbytes = PNG_ROWBYTES(png_ptr->row_info.pixel_depth,
          png_ptr->row_info.width);
    }
 #endif
 
 }
 
-#if defined(PNG_READ_PACK_SUPPORTED)
+#ifdef PNG_READ_PACK_SUPPORTED
 /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
  * without changing the actual values.  Thus, if you had a row with
  * a bit depth of 1, you would end up with bytes that only contained
  * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
  * png_do_shift() after this.
  */
 void /* PRIVATE */
 png_do_unpack(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_unpack");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL && row_info->bit_depth < 8)
 #else
    if (row_info->bit_depth < 8)
 #endif
    {
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;
 
       switch (row_info->bit_depth)
       {
@@ skipping 61 matching lines @@
             break;
          }
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_width * row_info->channels;
    }
 }
 #endif
 
-#if defined(PNG_READ_SHIFT_SUPPORTED)
+#ifdef PNG_READ_SHIFT_SUPPORTED
 /* Reverse the effects of png_do_shift.  This routine merely shifts the
  * pixels back to their significant bits values.  Thus, if you have
  * a row of bit depth 8, but only 5 are significant, this will shift
  * the values back to 0 through 31.
  */
 void /* PRIVATE */
 png_do_unshift(png_row_infop row_info, png_bytep row, png_color_8p sig_bits)
 {
    png_debug(1, "in png_do_unshift");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL && sig_bits != NULL &&
 #endif
        row_info->color_type != PNG_COLOR_TYPE_PALETTE)
    {
       int shift[4];
       int channels = 0;
       int c;
       png_uint_16 value = 0;
       png_uint_32 row_width = row_info->width;
 
@@ skipping 81 matching lines @@
                *bp++ = (png_byte)(value >> 8);
                *bp++ = (png_byte)(value & 0xff);
             }
             break;
          }
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
+#ifdef PNG_READ_16_TO_8_SUPPORTED
 /* Chop rows of bit depth 16 down to 8 */
 void /* PRIVATE */
 png_do_chop(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_chop");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL && row_info->bit_depth == 16)
 #else
    if (row_info->bit_depth == 16)
 #endif
    {
       png_bytep sp = row;
       png_bytep dp = row;
       png_uint_32 i;
       png_uint_32 istop = row_info->width * row_info->channels;
 
       for (i = 0; i<istop; i++, sp += 2, dp++)
       {
-#if defined(PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED)
+#ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
       /* This does a more accurate scaling of the 16-bit color
        * value, rather than a simple low-byte truncation.
        *
        * What the ideal calculation should be:
        *   *dp = (((((png_uint_32)(*sp) << 8) |
        *          (png_uint_32)(*(sp + 1))) * 255 + 127)
        *          / (png_uint_32)65535L;
        *
        * GRR: no, I think this is what it really should be:
        *   *dp = (((((png_uint_32)(*sp) << 8) |
@@ skipping 18 matching lines @@
          *dp = *sp;
 #endif
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_info->width * row_info->channels;
    }
 }
 #endif
 
-#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
 void /* PRIVATE */
 png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_read_swap_alpha");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL)
 #endif
    {
       png_uint_32 row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
       {
          /* This converts from RGBA to ARGB */
          if (row_info->bit_depth == 8)
          {
             png_bytep sp = row + row_info->rowbytes;
@@ skipping 66 matching lines @@
                *(--dp) = *(--sp);
                *(--dp) = save[0];
                *(--dp) = save[1];
             }
          }
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
 void /* PRIVATE */
 png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_read_invert_alpha");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL)
 #endif
    {
       png_uint_32 row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
       {
          /* This inverts the alpha channel in RGBA */
          if (row_info->bit_depth == 8)
          {
             png_bytep sp = row + row_info->rowbytes;
@@ skipping 72 matching lines @@
 */
                sp-=2;
                dp=sp;
             }
          }
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_FILLER_SUPPORTED)
+#ifdef PNG_READ_FILLER_SUPPORTED
 /* Add filler channel if we have RGB color */
 void /* PRIVATE */
 png_do_read_filler(png_row_infop row_info, png_bytep row,
    png_uint_32 filler, png_uint_32 flags)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
 
    png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
    png_byte lo_filler = (png_byte)(filler & 0xff);
 
    png_debug(1, "in png_do_read_filler");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL  && row_info != NULL &&
 #endif
        row_info->color_type == PNG_COLOR_TYPE_GRAY)
    {
       if (row_info->bit_depth == 8)
       {
          /* This changes the data from G to GX */
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
             png_bytep sp = row + (png_size_t)row_width;
@@ skipping 141 matching lines @@
             }
             row_info->channels = 4;
             row_info->pixel_depth = 64;
             row_info->rowbytes = row_width * 8;
          }
       }
    } /* COLOR_TYPE == RGB */
 }
 #endif
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 /* Expand grayscale files to RGB, with or without alpha */
 void /* PRIVATE */
 png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
 
    png_debug(1, "in png_do_gray_to_rgb");
+
    if (row_info->bit_depth >= 8 &&
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
       !(row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          if (row_info->bit_depth == 8)
          {
             png_bytep sp = row + (png_size_t)row_width - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
@@ skipping 52 matching lines @@
       }
       row_info->channels += (png_byte)2;
       row_info->color_type |= PNG_COLOR_MASK_COLOR;
       row_info->pixel_depth = (png_byte)(row_info->channels *
          row_info->bit_depth);
       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
    }
 }
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
 /* Reduce RGB files to grayscale, with or without alpha
  * using the equation given in Poynton's ColorFAQ at
  * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008)
  * New link:
  * <http://www.poynton.com/notes/colour_and_gamma/>
  * Charles Poynton poynton at poynton.com
  *
  *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
  *
  *  We approximate this with
@@ skipping 11 matching lines @@
 int /* PRIVATE */
 png_do_rgb_to_gray(png_structp png_ptr, png_row_infop row_info, png_bytep row)
 
 {
    png_uint_32 i;
 
    png_uint_32 row_width = row_info->width;
    int rgb_error = 0;
 
    png_debug(1, "in png_do_rgb_to_gray");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
       (row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
       png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
       png_uint_32 bc = png_ptr->rgb_to_gray_blue_coeff;
 
       if (row_info->color_type == PNG_COLOR_TYPE_RGB)
       {
@@ skipping 56 matching lines @@
                   red   = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
                   green = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
                   blue  = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
 
                   if (red == green && red == blue)
                      w = red;
                   else
                   {
                      png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff) >>
                                   png_ptr->gamma_shift][red>>8];
-                     png_uint_16 green_1 = png_ptr->gamma_16_to_1[(green&0xff) >>
+                     png_uint_16 green_1 =
+                         png_ptr->gamma_16_to_1[(green&0xff) >>
                                   png_ptr->gamma_shift][green>>8];
                      png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff) >>
                                   png_ptr->gamma_shift][blue>>8];
                      png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
                                   + bc*blue_1)>>15);
                      w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
                          png_ptr->gamma_shift][gray16 >> 8];
                      rgb_error |= 1;
                   }
 
@@ skipping 75 matching lines @@
 
                   red   = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
                   green = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
                   blue  = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
 
                   if (red == green && red == blue)
                      w = red;
                   else
                   {
                      png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff) >>
-                                  png_ptr->gamma_shift][red>>8];
-                     png_uint_16 green_1 = png_ptr->gamma_16_to_1[(green&0xff) >>
-                                  png_ptr->gamma_shift][green>>8];
+                         png_ptr->gamma_shift][red>>8];
+                     png_uint_16 green_1 =
+                         png_ptr->gamma_16_to_1[(green&0xff) >>
+                         png_ptr->gamma_shift][green>>8];
                      png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff) >>
-                                  png_ptr->gamma_shift][blue>>8];
+                         png_ptr->gamma_shift][blue>>8];
                      png_uint_16 gray16  = (png_uint_16)((rc * red_1
-                                  + gc * green_1 + bc * blue_1)>>15);
+                         + gc * green_1 + bc * blue_1)>>15);
                      w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
                          png_ptr->gamma_shift][gray16 >> 8];
                      rgb_error |= 1;
                   }
 
                   *(dp++) = (png_byte)((w>>8) & 0xff);
                   *(dp++) = (png_byte)(w & 0xff);
                   *(dp++) = *(sp++);  /* alpha */
                   *(dp++) = *(sp++);
                }
@@ skipping 37 matching lines @@
  */
 void PNGAPI
 png_build_grayscale_palette(int bit_depth, png_colorp palette)
 {
    int num_palette;
    int color_inc;
    int i;
    int v;
 
    png_debug(1, "in png_do_build_grayscale_palette");
+
    if (palette == NULL)
       return;
 
    switch (bit_depth)
    {
       case 1:
          num_palette = 2;
          color_inc = 0xff;
          break;
 
@@ skipping 20 matching lines @@
 
    for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
    {
       palette[i].red = (png_byte)v;
       palette[i].green = (png_byte)v;
       palette[i].blue = (png_byte)v;
    }
 }
 
 /* This function is currently unused.  Do we really need it? */
-#if defined(PNG_READ_DITHER_SUPPORTED) && defined(PNG_CORRECT_PALETTE_SUPPORTED)
+#if defined(PNG_READ_DITHER_SUPPORTED) && \
+  defined(PNG_CORRECT_PALETTE_SUPPORTED)
 void /* PRIVATE */
 png_correct_palette(png_structp png_ptr, png_colorp palette,
    int num_palette)
 {
    png_debug(1, "in png_correct_palette");
+
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
-    defined(PNG_READ_GAMMA_SUPPORTED) && defined(PNG_FLOATING_POINT_SUPPORTED)
+    defined(PNG_READ_GAMMA_SUPPORTED) && \
+  defined(PNG_FLOATING_POINT_SUPPORTED)
    if (png_ptr->transformations & (PNG_GAMMA | PNG_BACKGROUND))
    {
       png_color back, back_1;
 
       if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
       {
          back.red = png_ptr->gamma_table[png_ptr->background.red];
          back.green = png_ptr->gamma_table[png_ptr->background.green];
          back.blue = png_ptr->gamma_table[png_ptr->background.blue];
 
          back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
          back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
          back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
       }
       else
       {
          double g;
 
          g = 1.0 / (png_ptr->background_gamma * png_ptr->screen_gamma);
 
-         if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_SCREEN ||
-             fabs(g - 1.0) < PNG_GAMMA_THRESHOLD)
+         if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_SCREEN
+             || fabs(g - 1.0) < PNG_GAMMA_THRESHOLD)
          {
             back.red = png_ptr->background.red;
             back.green = png_ptr->background.green;
             back.blue = png_ptr->background.blue;
          }
          else
          {
             back.red =
                (png_byte)(pow((double)png_ptr->background.red/255, g) *
                 255.0 + 0.5);
@@ skipping 66 matching lines @@
             {
                palette[i].red = png_ptr->gamma_table[palette[i].red];
                palette[i].green = png_ptr->gamma_table[palette[i].green];
                palette[i].blue = png_ptr->gamma_table[palette[i].blue];
             }
          }
       }
    }
    else
 #endif
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
    if (png_ptr->transformations & PNG_GAMMA)
    {
       int i;
 
       for (i = 0; i < num_palette; i++)
       {
          palette[i].red = png_ptr->gamma_table[palette[i].red];
          palette[i].green = png_ptr->gamma_table[palette[i].green];
          palette[i].blue = png_ptr->gamma_table[palette[i].blue];
       }
    }
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    else
 #endif
 #endif
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    if (png_ptr->transformations & PNG_BACKGROUND)
    {
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          png_color back;
 
          back.red   = (png_byte)png_ptr->background.red;
          back.green = (png_byte)png_ptr->background.green;
          back.blue  = (png_byte)png_ptr->background.blue;
 
@@ skipping 28 matching lines @@
                palette[i].green = (png_byte)png_ptr->background.green;
                palette[i].blue = (png_byte)png_ptr->background.blue;
             }
          }
       }
    }
 #endif
 }
 #endif
 
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
 /* Replace any alpha or transparency with the supplied background color.
  * "background" is already in the screen gamma, while "background_1" is
  * at a gamma of 1.0.  Paletted files have already been taken care of.
  */
 void /* PRIVATE */
 png_do_background(png_row_infop row_info, png_bytep row,
    png_color_16p trans_values, png_color_16p background
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
    , png_color_16p background_1,
    png_bytep gamma_table, png_bytep gamma_from_1, png_bytep gamma_to_1,
    png_uint_16pp gamma_16, png_uint_16pp gamma_16_from_1,
    png_uint_16pp gamma_16_to_1, int gamma_shift
 #endif
    )
 {
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
    int shift;
 
    png_debug(1, "in png_do_background");
+
    if (background != NULL &&
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
       (!(row_info->color_type & PNG_COLOR_MASK_ALPHA) ||
       (row_info->color_type != PNG_COLOR_TYPE_PALETTE && trans_values)))
    {
       switch (row_info->color_type)
       {
          case PNG_COLOR_TYPE_GRAY:
          {
             switch (row_info->bit_depth)
@@ skipping 16 matching lines @@
                         sp++;
                      }
                      else
                         shift--;
                   }
                   break;
                }
 
                case 2:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      shift = 6;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x03)
                             == trans_values->gray)
                         {
                            *sp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
@@ skipping 36 matching lines @@
                         }
                         else
                            shift -= 2;
                      }
                   }
                   break;
                }
 
                case 4:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      shift = 4;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x0f)
                             == trans_values->gray)
                         {
                            *sp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
@@ skipping 36 matching lines @@
                         }
                         else
                            shift -= 4;
                      }
                   }
                   break;
                }
 
                case 8:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp++)
                      {
                         if (*sp == trans_values->gray)
                         {
                            *sp = (png_byte)background->gray;
                         }
                         else
@@ skipping 12 matching lines @@
                         {
                            *sp = (png_byte)background->gray;
                         }
                      }
                   }
                   break;
                }
 
                case 16:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 2)
                      {
                         png_uint_16 v;
 
                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         if (v == trans_values->gray)
                         {
@@ skipping 28 matching lines @@
                   break;
                }
             }
             break;
          }
 
          case PNG_COLOR_TYPE_RGB:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_table != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 3)
                   {
                      if (*sp == trans_values->red &&
                         *(sp + 1) == trans_values->green &&
                         *(sp + 2) == trans_values->blue)
                      {
                         *sp = (png_byte)background->red;
@@ skipping 20 matching lines @@
                      {
                         *sp = (png_byte)background->red;
                         *(sp + 1) = (png_byte)background->green;
                         *(sp + 2) = (png_byte)background->blue;
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 6)
                   {
                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                      png_uint_16 g = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
                      png_uint_16 b = (png_uint_16)(((*(sp+4)) << 8) + *(sp+5));
                      if (r == trans_values->red && g == trans_values->green &&
                         b == trans_values->blue)
@@ skipping 43 matching lines @@
                   }
                }
             }
             break;
          }
 
          case PNG_COLOR_TYPE_GRAY_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 2, dp++)
                   {
                      png_uint_16 a = *(sp + 1);
 
                      if (a == 0xff)
@@ skipping 21 matching lines @@
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 2, dp++)
                   {
                      png_byte a = *(sp + 1);
 
                      if (a == 0xff)
                      {
                         *dp = *sp;
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                      else if (a == 0)
                      {
                         *dp = (png_byte)background->gray;
                      }
                      else
                      {
                         png_composite(*dp, *sp, a, background_1->gray);
                      }
 #else
                      *dp = (png_byte)background->gray;
 #endif
                   }
                }
             }
             else /* if (png_ptr->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 4, dp += 2)
                   {
                      png_uint_16 a = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
 
                      if (a == (png_uint_16)0xffff)
                      {
                         png_uint_16 v;
 
                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                         *dp = (png_byte)((v >> 8) & 0xff);
                         *(dp + 1) = (png_byte)(v & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                      else if (a == 0)
 #else
                      else
 #endif
                      {
                         /* Background is already in screen gamma */
                         *dp = (png_byte)((background->gray >> 8) & 0xff);
                         *(dp + 1) = (png_byte)(background->gray & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                      else
                      {
                         png_uint_16 g, v, w;
 
                         g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                         png_composite_16(v, g, a, background_1->gray);
                         w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
                         *dp = (png_byte)((w >> 8) & 0xff);
                         *(dp + 1) = (png_byte)(w & 0xff);
                      }
 #endif
                   }
                }
                else
 #endif
                {
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 4, dp += 2)
                   {
                      png_uint_16 a = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
                      if (a == (png_uint_16)0xffff)
                      {
                         png_memcpy(dp, sp, 2);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                      else if (a == 0)
 #else
                      else
 #endif
                      {
                         *dp = (png_byte)((background->gray >> 8) & 0xff);
                         *(dp + 1) = (png_byte)(background->gray & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                      else
                      {
                         png_uint_16 g, v;
 
                         g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         png_composite_16(v, g, a, background_1->gray);
                         *dp = (png_byte)((v >> 8) & 0xff);
                         *(dp + 1) = (png_byte)(v & 0xff);
                      }
 #endif
                   }
                }
             }
             break;
          }
 
          case PNG_COLOR_TYPE_RGB_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 4, dp += 3)
                   {
                      png_byte a = *(sp + 3);
 
                      if (a == 0xff)
@@ skipping 52 matching lines @@
                         png_composite(*(dp + 1), *(sp + 1), a,
                            background->green);
                         png_composite(*(dp + 2), *(sp + 2), a,
                            background->blue);
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
                   dp = row;
                   for (i = 0; i < row_width; i++, sp += 8, dp += 6)
                   {
                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                          << 8) + (png_uint_16)(*(sp + 7)));
                      if (a == (png_uint_16)0xffff)
@@ skipping 96 matching lines @@
          row_info->color_type &= ~PNG_COLOR_MASK_ALPHA;
          row_info->channels--;
          row_info->pixel_depth = (png_byte)(row_info->channels *
             row_info->bit_depth);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
 /* Gamma correct the image, avoiding the alpha channel.  Make sure
  * you do this after you deal with the transparency issue on grayscale
  * or RGB images. If your bit depth is 8, use gamma_table, if it
  * is 16, use gamma_16_table and gamma_shift.  Build these with
  * build_gamma_table().
  */
 void /* PRIVATE */
 png_do_gamma(png_row_infop row_info, png_bytep row,
    png_bytep gamma_table, png_uint_16pp gamma_16_table,
    int gamma_shift)
 {
    png_bytep sp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
    png_debug(1, "in png_do_gamma");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
        ((row_info->bit_depth <= 8 && gamma_table != NULL) ||
         (row_info->bit_depth == 16 && gamma_16_table != NULL)))
    {
       switch (row_info->color_type)
       {
          case PNG_COLOR_TYPE_RGB:
          {
             if (row_info->bit_depth == 8)
@@ skipping 102 matching lines @@
             {
                sp = row;
                for (i = 0; i < row_width; i += 4)
                {
                   int a = *sp & 0xc0;
                   int b = *sp & 0x30;
                   int c = *sp & 0x0c;
                   int d = *sp & 0x03;
 
                   *sp = (png_byte)(
-                        ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
-                        ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
-                        ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
-                        ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
+                      ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
+                      ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
+                      ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
+                      ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
                   sp++;
                }
             }
 
             if (row_info->bit_depth == 4)
             {
                sp = row;
                for (i = 0; i < row_width; i += 2)
                {
                   int msb = *sp & 0xf0;
                   int lsb = *sp & 0x0f;
 
                   *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
-                          | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
+                      | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
                   sp++;
                }
             }
 
             else if (row_info->bit_depth == 8)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   *sp = gamma_table[*sp];
@@ skipping 12 matching lines @@
                   sp += 2;
                }
             }
             break;
          }
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expands a palette row to an RGB or RGBA row depending
  * upon whether you supply trans and num_trans.
  */
 void /* PRIVATE */
 png_do_expand_palette(png_row_infop row_info, png_bytep row,
    png_colorp palette, png_bytep trans, int num_trans)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
    png_debug(1, "in png_do_expand_palette");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
        row_info->color_type == PNG_COLOR_TYPE_PALETTE)
    {
       if (row_info->bit_depth < 8)
       {
          switch (row_info->bit_depth)
          {
             case 1:
             {
@@ skipping 124 matching lines @@
 void /* PRIVATE */
 png_do_expand(png_row_infop row_info, png_bytep row,
    png_color_16p trans_value)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
    png_debug(1, "in png_do_expand");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL)
 #endif
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          png_uint_16 gray = (png_uint_16)(trans_value ? trans_value->gray : 0);
 
          if (row_info->bit_depth < 8)
          {
             switch (row_info->bit_depth)
@@ skipping 180 matching lines @@
          }
          row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          row_info->channels = 4;
          row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
+#ifdef PNG_READ_DITHER_SUPPORTED
 void /* PRIVATE */
 png_do_dither(png_row_infop row_info, png_bytep row,
     png_bytep palette_lookup, png_bytep dither_lookup)
 {
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
    png_debug(1, "in png_do_dither");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+
+#ifdef PNG_USELESS_TESTS_SUPPORTED
    if (row != NULL && row_info != NULL)
 #endif
    {
       if (row_info->color_type == PNG_COLOR_TYPE_RGB &&
          palette_lookup && row_info->bit_depth == 8)
       {
          int r, g, b, p;
          sp = row;
          dp = row;
          for (i = 0; i < row_width; i++)
@@ skipping 61 matching lines @@
          for (i = 0; i < row_width; i++, sp++)
          {
             *sp = dither_lookup[*sp];
          }
       }
    }
 }
 #endif
 
 #ifdef PNG_FLOATING_POINT_SUPPORTED
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
 static PNG_CONST int png_gamma_shift[] =
    {0x10, 0x21, 0x42, 0x84, 0x110, 0x248, 0x550, 0xff0, 0x00};
 
 /* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
  * tables, we don't make a full table if we are reducing to 8-bit in
  * the future.  Note also how the gamma_16 tables are segmented so that
  * we don't need to allocate > 64K chunks for a full 16-bit table.
+ *
+ * See the PNG extensions document for an integer algorithm for creating
+ * the gamma tables.  Maybe we will implement that here someday.
+ *
+ * We should only reach this point if
+ *
+ *      the file_gamma is known (i.e., the gAMA or sRGB chunk is present,
+ *      or the application has provided a file_gamma)
+ *
+ *   AND
+ *      {
+ *         the screen_gamma is known
+ *      OR
+ *
+ *         RGB_to_gray transformation is being performed
+ *      }
+ *
+ *   AND
+ *      {
+ *         the screen_gamma is different from the reciprocal of the
+ *         file_gamma by more than the specified threshold
+ *
+ *      OR
+ *
+ *         a background color has been specified and the file_gamma
+ *         and screen_gamma are not 1.0, within the specified threshold.
+ *      }
  */
+
 void /* PRIVATE */
 png_build_gamma_table(png_structp png_ptr)
 {
   png_debug(1, "in png_build_gamma_table");
 
   if (png_ptr->bit_depth <= 8)
   {
      int i;
      double g;
 
@@ skipping 89 matching lines @@
 
      png_ptr->gamma_shift = (png_byte)shift;
 
      num = (1 << (8 - shift));
 
      if (png_ptr->screen_gamma > .000001)
         g = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
      else
         g = 1.0;
 
-     png_ptr->gamma_16_table = (png_uint_16pp)png_malloc(png_ptr,
+     png_ptr->gamma_16_table = (png_uint_16pp)png_calloc(png_ptr,
         (png_uint_32)(num * png_sizeof(png_uint_16p)));
-     png_memset(png_ptr->gamma_16_table, 0, num * png_sizeof(png_uint_16p)); 
 
      if (png_ptr->transformations & (PNG_16_TO_8 | PNG_BACKGROUND))
      {
         double fin, fout;
         png_uint_32 last, max;
 
         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_table[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * png_sizeof(png_uint_16)));
@@ skipping 39 matching lines @@
         }
      }
 
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
      if (png_ptr->transformations & (PNG_BACKGROUND | PNG_RGB_TO_GRAY))
      {
 
         g = 1.0 / (png_ptr->gamma);
 
-        png_ptr->gamma_16_to_1 = (png_uint_16pp)png_malloc(png_ptr,
+        png_ptr->gamma_16_to_1 = (png_uint_16pp)png_calloc(png_ptr,
            (png_uint_32)(num * png_sizeof(png_uint_16p )));
-        png_memset(png_ptr->gamma_16_to_1, 0, num * png_sizeof(png_uint_16p)); 
 
         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_to_1[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * png_sizeof(png_uint_16)));
 
            ig = (((png_uint_32)i *
               (png_uint_32)png_gamma_shift[shift]) >> 4);
            for (j = 0; j < 256; j++)
            {
               png_ptr->gamma_16_to_1[i][j] =
                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
                     65535.0, g) * 65535.0 + .5);
            }
         }
 
         if (png_ptr->screen_gamma > 0.000001)
            g = 1.0 / png_ptr->screen_gamma;
 
         else
            g = png_ptr->gamma;   /* Probably doing rgb_to_gray */
 
-        png_ptr->gamma_16_from_1 = (png_uint_16pp)png_malloc(png_ptr,
+        png_ptr->gamma_16_from_1 = (png_uint_16pp)png_calloc(png_ptr,
            (png_uint_32)(num * png_sizeof(png_uint_16p)));
-        png_memset(png_ptr->gamma_16_from_1, 0,
-           num * png_sizeof(png_uint_16p)); 
 
         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_from_1[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * png_sizeof(png_uint_16)));
 
            ig = (((png_uint_32)i *
               (png_uint_32)png_gamma_shift[shift]) >> 4);
 
            for (j = 0; j < 256; j++)
            {
               png_ptr->gamma_16_from_1[i][j] =
                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
                     65535.0, g) * 65535.0 + .5);
            }
         }
      }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_RGB_TO_GRAY_SUPPORTED */
   }
 }
 #endif
 /* To do: install integer version of png_build_gamma_table here */
 #endif
 
-#if defined(PNG_MNG_FEATURES_SUPPORTED)
+#ifdef PNG_MNG_FEATURES_SUPPORTED
 /* Undoes intrapixel differencing  */
 void /* PRIVATE */
 png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_read_intrapixel");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
+#ifdef PNG_USELESS_TESTS_SUPPORTED
        row != NULL && row_info != NULL &&
 #endif
        (row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       int bytes_per_pixel;
       png_uint_32 row_width = row_info->width;
       if (row_info->bit_depth == 8)
       {
          png_bytep rp;
          png_uint_32 i;
@@ skipping 37 matching lines @@
             *(rp  ) = (png_byte)((red >> 8) & 0xff);
             *(rp+1) = (png_byte)(red & 0xff);
             *(rp+4) = (png_byte)((blue >> 8) & 0xff);
             *(rp+5) = (png_byte)(blue & 0xff);
          }
       }
    }
 }
 #endif /* PNG_MNG_FEATURES_SUPPORTED */
 #endif /* PNG_READ_SUPPORTED */