Update libpng to 1.2.38 to patch a minor security issue.

1 files changed, 178 insertions, 45 deletions

diff --git a/pngpread.c b/pngpread.c
index b06fbad..9eddd6e 100644
--- a/pngpread.c
+++ b/pngpread.c
@@ -1,18 +1,21 @@
 
 /* pngpread.c - read a png file in push mode
  *
- * Last changed in libpng 1.2.32 [September 18, 2008]
- * For conditions of distribution and use, see copyright notice in png.h
- * Copyright (c) 1998-2008 Glenn Randers-Pehrson
+ * Last changed in libpng 1.2.37 [July 16, 2009]
+ * Copyright (c) 1998-2009 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
  */
 
 #define PNG_INTERNAL
 #include "png.h"
 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
 
-/* push model modes */
+/* Push model modes */
 #define PNG_READ_SIG_MODE   0
 #define PNG_READ_CHUNK_MODE 1
 #define PNG_READ_IDAT_MODE  2
@@ -27,7 +30,9 @@ void PNGAPI
 png_process_data(png_structp png_ptr, png_infop info_ptr,
    png_bytep buffer, png_size_t buffer_size)
 {
-   if (png_ptr == NULL || info_ptr == NULL) return;
+   if (png_ptr == NULL || info_ptr == NULL)
+      return;
+
    png_push_restore_buffer(png_ptr, buffer, buffer_size);
 
    while (png_ptr->buffer_size)
@@ -42,7 +47,9 @@ png_process_data(png_structp png_ptr, png_infop info_ptr,
 void /* PRIVATE */
 png_process_some_data(png_structp png_ptr, png_infop info_ptr)
 {
-   if (png_ptr == NULL) return;
+   if (png_ptr == NULL)
+      return;
+
    switch (png_ptr->process_mode)
    {
       case PNG_READ_SIG_MODE:
@@ -50,22 +57,26 @@ png_process_some_data(png_structp png_ptr, png_infop info_ptr)
          png_push_read_sig(png_ptr, info_ptr);
          break;
       }
+
       case PNG_READ_CHUNK_MODE:
       {
          png_push_read_chunk(png_ptr, info_ptr);
          break;
       }
+
       case PNG_READ_IDAT_MODE:
       {
          png_push_read_IDAT(png_ptr);
          break;
       }
+
 #if defined(PNG_READ_tEXt_SUPPORTED)
       case PNG_READ_tEXt_MODE:
       {
          png_push_read_tEXt(png_ptr, info_ptr);
          break;
       }
+
 #endif
 #if defined(PNG_READ_zTXt_SUPPORTED)
       case PNG_READ_zTXt_MODE:
@@ -73,6 +84,7 @@ png_process_some_data(png_structp png_ptr, png_infop info_ptr)
          png_push_read_zTXt(png_ptr, info_ptr);
          break;
       }
+
 #endif
 #if defined(PNG_READ_iTXt_SUPPORTED)
       case PNG_READ_iTXt_MODE:
@@ -80,12 +92,14 @@ png_process_some_data(png_structp png_ptr, png_infop info_ptr)
          png_push_read_iTXt(png_ptr, info_ptr);
          break;
       }
+
 #endif
       case PNG_SKIP_MODE:
       {
          png_push_crc_finish(png_ptr);
          break;
       }
+
       default:
       {
          png_ptr->buffer_size = 0;
@@ -224,13 +238,16 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
    {
       if (png_ptr->push_length != 13)
          png_error(png_ptr, "Invalid IHDR length");
+
       if (png_ptr->push_length + 4 > png_ptr->buffer_size)
       {
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_IHDR(png_ptr, info_ptr, png_ptr->push_length);
    }
+
    else if (!png_memcmp(png_ptr->chunk_name, png_IEND, 4))
    {
       if (png_ptr->push_length + 4 > png_ptr->buffer_size)
@@ -238,11 +255,13 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_IEND(png_ptr, info_ptr, png_ptr->push_length);
 
       png_ptr->process_mode = PNG_READ_DONE_MODE;
       png_push_have_end(png_ptr, info_ptr);
    }
+
 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
    else if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name))
    {
@@ -251,20 +270,26 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
          png_ptr->mode |= PNG_HAVE_IDAT;
+
       png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length);
+
       if (!png_memcmp(png_ptr->chunk_name, png_PLTE, 4))
          png_ptr->mode |= PNG_HAVE_PLTE;
+
       else if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
       {
          if (!(png_ptr->mode & PNG_HAVE_IHDR))
             png_error(png_ptr, "Missing IHDR before IDAT");
+
          else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
                   !(png_ptr->mode & PNG_HAVE_PLTE))
             png_error(png_ptr, "Missing PLTE before IDAT");
       }
    }
+
 #endif
    else if (!png_memcmp(png_ptr->chunk_name, png_PLTE, 4))
    {
@@ -275,23 +300,26 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
       }
       png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
    }
+
    else if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
    {
       /* If we reach an IDAT chunk, this means we have read all of the
        * header chunks, and we can start reading the image (or if this
        * is called after the image has been read - we have an error).
        */
-     if (!(png_ptr->mode & PNG_HAVE_IHDR))
-       png_error(png_ptr, "Missing IHDR before IDAT");
-     else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
-         !(png_ptr->mode & PNG_HAVE_PLTE))
-       png_error(png_ptr, "Missing PLTE before IDAT");
+
+      if (!(png_ptr->mode & PNG_HAVE_IHDR))
+         png_error(png_ptr, "Missing IHDR before IDAT");
+
+      else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
+          !(png_ptr->mode & PNG_HAVE_PLTE))
+         png_error(png_ptr, "Missing PLTE before IDAT");
 
       if (png_ptr->mode & PNG_HAVE_IDAT)
       {
          if (!(png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
-           if (png_ptr->push_length == 0)
-              return;
+            if (png_ptr->push_length == 0)
+               return;
 
          if (png_ptr->mode & PNG_AFTER_IDAT)
             png_error(png_ptr, "Too many IDAT's found");
@@ -305,6 +333,7 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
       png_ptr->zstream.next_out = png_ptr->row_buf;
       return;
    }
+
 #if defined(PNG_READ_gAMA_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_gAMA, 4))
    {
@@ -313,8 +342,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_sBIT_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_sBIT, 4))
@@ -324,8 +355,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_cHRM_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_cHRM, 4))
@@ -335,8 +368,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_sRGB_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_sRGB, 4))
@@ -346,8 +381,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_sRGB(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_iCCP_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_iCCP, 4))
@@ -357,8 +394,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_iCCP(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_sPLT_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_sPLT, 4))
@@ -368,8 +407,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_sPLT(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_tRNS_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_tRNS, 4))
@@ -379,8 +420,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_bKGD_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_bKGD, 4))
@@ -390,8 +433,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_hIST_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_hIST, 4))
@@ -401,8 +446,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_pHYs_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_pHYs, 4))
@@ -412,8 +459,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_oFFs_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_oFFs, 4))
@@ -423,9 +472,11 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
    }
 #endif
+
 #if defined(PNG_READ_pCAL_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_pCAL, 4))
    {
@@ -434,8 +485,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_sCAL_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_sCAL, 4))
@@ -445,8 +498,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_sCAL(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_tIME_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_tIME, 4))
@@ -456,8 +511,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_tEXt_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_tEXt, 4))
@@ -467,8 +524,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_push_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_zTXt_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_zTXt, 4))
@@ -478,8 +537,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_push_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
 #if defined(PNG_READ_iTXt_SUPPORTED)
    else if (!png_memcmp(png_ptr->chunk_name, png_iTXt, 4))
@@ -489,8 +550,10 @@ png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
          png_push_save_buffer(png_ptr);
          return;
       }
+
       png_push_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
    }
+
 #endif
    else
    {
@@ -565,7 +628,9 @@ png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, png_size_t length)
 {
    png_bytep ptr;
 
-   if (png_ptr == NULL) return;
+   if (png_ptr == NULL)
+      return;
+
    ptr = buffer;
    if (png_ptr->save_buffer_size)
    {
@@ -589,6 +654,7 @@ png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, png_size_t length)
 
       if (length < png_ptr->current_buffer_size)
          save_size = length;
+
       else
          save_size = png_ptr->current_buffer_size;
 
@@ -629,6 +695,7 @@ png_push_save_buffer(png_structp png_ptr)
       {
         png_error(png_ptr, "Potential overflow of save_buffer");
       }
+
       new_max = png_ptr->save_buffer_size + png_ptr->current_buffer_size + 256;
       old_buffer = png_ptr->save_buffer;
       png_ptr->save_buffer = (png_bytep)png_malloc(png_ptr,
@@ -697,7 +764,8 @@ png_push_read_IDAT(png_structp png_ptr)
       if (png_ptr->idat_size < (png_uint_32)png_ptr->save_buffer_size)
       {
          save_size = (png_size_t)png_ptr->idat_size;
-         /* check for overflow */
+
+         /* Check for overflow */
          if ((png_uint_32)save_size != png_ptr->idat_size)
             png_error(png_ptr, "save_size overflowed in pngpread");
       }
@@ -705,8 +773,10 @@ png_push_read_IDAT(png_structp png_ptr)
          save_size = png_ptr->save_buffer_size;
 
       png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);
+
       if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
          png_process_IDAT_data(png_ptr, png_ptr->save_buffer_ptr, save_size);
+
       png_ptr->idat_size -= save_size;
       png_ptr->buffer_size -= save_size;
       png_ptr->save_buffer_size -= save_size;
@@ -719,7 +789,8 @@ png_push_read_IDAT(png_structp png_ptr)
       if (png_ptr->idat_size < (png_uint_32)png_ptr->current_buffer_size)
       {
          save_size = (png_size_t)png_ptr->idat_size;
-         /* check for overflow */
+
+         /* Check for overflow */
          if ((png_uint_32)save_size != png_ptr->idat_size)
             png_error(png_ptr, "save_size overflowed in pngpread");
       }
@@ -769,6 +840,7 @@ png_process_IDAT_data(png_structp png_ptr, png_bytep buffer,
          {
             if (png_ptr->zstream.avail_in)
                png_error(png_ptr, "Extra compressed data");
+
             if (!(png_ptr->zstream.avail_out))
             {
                png_push_process_row(png_ptr);
@@ -780,6 +852,7 @@ png_process_IDAT_data(png_structp png_ptr, png_bytep buffer,
          }
          else if (ret == Z_BUF_ERROR)
             break;
+
          else
             png_error(png_ptr, "Decompression Error");
       }
@@ -801,6 +874,7 @@ png_process_IDAT_data(png_structp png_ptr, png_bytep buffer,
          png_ptr->zstream.avail_out = (uInt)png_ptr->irowbytes;
          png_ptr->zstream.next_out = png_ptr->row_buf;
       }
+
       else
          break;
    }
@@ -829,7 +903,7 @@ png_push_process_row(png_structp png_ptr)
       png_do_read_transformations(png_ptr);
 
 #if defined(PNG_READ_INTERLACING_SUPPORTED)
-   /* blow up interlaced rows to full size */
+   /* Blow up interlaced rows to full size */
    if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
    {
       if (png_ptr->pass < 6)
@@ -847,9 +921,10 @@ png_push_process_row(png_structp png_ptr)
             for (i = 0; i < 8 && png_ptr->pass == 0; i++)
             {
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
-               png_read_push_finish_row(png_ptr); /* updates png_ptr->pass */
+               png_read_push_finish_row(png_ptr); /* Updates png_ptr->pass */
             }
-            if (png_ptr->pass == 2) /* pass 1 might be empty */
+
+            if (png_ptr->pass == 2) /* Pass 1 might be empty */
             {
                for (i = 0; i < 4 && png_ptr->pass == 2; i++)
                {
@@ -857,6 +932,7 @@ png_push_process_row(png_structp png_ptr)
                   png_read_push_finish_row(png_ptr);
                }
             }
+
             if (png_ptr->pass == 4 && png_ptr->height <= 4)
             {
                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
@@ -865,13 +941,16 @@ png_push_process_row(png_structp png_ptr)
                   png_read_push_finish_row(png_ptr);
                }
             }
+
             if (png_ptr->pass == 6 && png_ptr->height <= 4)
             {
                 png_push_have_row(png_ptr, png_bytep_NULL);
                 png_read_push_finish_row(png_ptr);
             }
+
             break;
          }
+
          case 1:
          {
             int i;
@@ -880,7 +959,8 @@ png_push_process_row(png_structp png_ptr)
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
                png_read_push_finish_row(png_ptr);
             }
-            if (png_ptr->pass == 2) /* skip top 4 generated rows */
+
+            if (png_ptr->pass == 2) /* Skip top 4 generated rows */
             {
                for (i = 0; i < 4 && png_ptr->pass == 2; i++)
                {
@@ -888,22 +968,27 @@ png_push_process_row(png_structp png_ptr)
                   png_read_push_finish_row(png_ptr);
                }
             }
+
             break;
          }
+
          case 2:
          {
             int i;
+
             for (i = 0; i < 4 && png_ptr->pass == 2; i++)
             {
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
                png_read_push_finish_row(png_ptr);
             }
+
             for (i = 0; i < 4 && png_ptr->pass == 2; i++)
             {
                png_push_have_row(png_ptr, png_bytep_NULL);
                png_read_push_finish_row(png_ptr);
             }
-            if (png_ptr->pass == 4) /* pass 3 might be empty */
+
+            if (png_ptr->pass == 4) /* Pass 3 might be empty */
             {
                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
                {
@@ -911,17 +996,21 @@ png_push_process_row(png_structp png_ptr)
                   png_read_push_finish_row(png_ptr);
                }
             }
+
             break;
          }
+
          case 3:
          {
             int i;
+
             for (i = 0; i < 4 && png_ptr->pass == 3; i++)
             {
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
                png_read_push_finish_row(png_ptr);
             }
-            if (png_ptr->pass == 4) /* skip top two generated rows */
+
+            if (png_ptr->pass == 4) /* Skip top two generated rows */
             {
                for (i = 0; i < 2 && png_ptr->pass == 4; i++)
                {
@@ -929,49 +1018,61 @@ png_push_process_row(png_structp png_ptr)
                   png_read_push_finish_row(png_ptr);
                }
             }
+
             break;
          }
+
          case 4:
          {
             int i;
+
             for (i = 0; i < 2 && png_ptr->pass == 4; i++)
             {
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
                png_read_push_finish_row(png_ptr);
             }
+
             for (i = 0; i < 2 && png_ptr->pass == 4; i++)
             {
                png_push_have_row(png_ptr, png_bytep_NULL);
                png_read_push_finish_row(png_ptr);
             }
-            if (png_ptr->pass == 6) /* pass 5 might be empty */
+
+            if (png_ptr->pass == 6) /* Pass 5 might be empty */
             {
                png_push_have_row(png_ptr, png_bytep_NULL);
                png_read_push_finish_row(png_ptr);
             }
+
             break;
          }
+
          case 5:
          {
             int i;
+
             for (i = 0; i < 2 && png_ptr->pass == 5; i++)
             {
                png_push_have_row(png_ptr, png_ptr->row_buf + 1);
                png_read_push_finish_row(png_ptr);
             }
-            if (png_ptr->pass == 6) /* skip top generated row */
+
+            if (png_ptr->pass == 6) /* Skip top generated row */
             {
                png_push_have_row(png_ptr, png_bytep_NULL);
                png_read_push_finish_row(png_ptr);
             }
+
             break;
          }
          case 6:
          {
             png_push_have_row(png_ptr, png_ptr->row_buf + 1);
             png_read_push_finish_row(png_ptr);
+
             if (png_ptr->pass != 6)
                break;
+
             png_push_have_row(png_ptr, png_bytep_NULL);
             png_read_push_finish_row(png_ptr);
          }
@@ -989,18 +1090,18 @@ void /* PRIVATE */
 png_read_push_finish_row(png_structp png_ptr)
 {
 #ifdef PNG_USE_LOCAL_ARRAYS
-   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */
+   /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
 
-   /* start of interlace block */
+   /* Start of interlace block */
    PNG_CONST int FARDATA png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};
 
-   /* offset to next interlace block */
+   /* Offset to next interlace block */
    PNG_CONST int FARDATA png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};
 
-   /* start of interlace block in the y direction */
+   /* Start of interlace block in the y direction */
    PNG_CONST int FARDATA png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};
 
-   /* offset to next interlace block in the y direction */
+   /* Offset to next interlace block in the y direction */
    PNG_CONST int FARDATA png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};
 
    /* Height of interlace block.  This is not currently used - if you need
@@ -1013,6 +1114,7 @@ png_read_push_finish_row(png_structp png_ptr)
    if (png_ptr->row_number < png_ptr->num_rows)
       return;
 
+#if defined(PNG_READ_INTERLACING_SUPPORTED)
    if (png_ptr->interlaced)
    {
       png_ptr->row_number = 0;
@@ -1028,6 +1130,7 @@ png_read_push_finish_row(png_structp png_ptr)
 
          if (png_ptr->pass > 7)
             png_ptr->pass--;
+
          if (png_ptr->pass >= 7)
             break;
 
@@ -1049,6 +1152,7 @@ png_read_push_finish_row(png_structp png_ptr)
 
       } while (png_ptr->iwidth == 0 || png_ptr->num_rows == 0);
    }
+#endif /* PNG_READ_INTERLACING_SUPPORTED */
 }
 
 #if defined(PNG_READ_tEXt_SUPPORTED)
@@ -1059,7 +1163,7 @@ png_push_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32
    if (!(png_ptr->mode & PNG_HAVE_IHDR) || (png_ptr->mode & PNG_HAVE_IEND))
       {
          png_error(png_ptr, "Out of place tEXt");
-         info_ptr = info_ptr; /* to quiet some compiler warnings */
+         info_ptr = info_ptr; /* To quiet some compiler warnings */
       }
 
 #ifdef PNG_MAX_MALLOC_64K
@@ -1091,8 +1195,10 @@ png_push_read_tEXt(png_structp png_ptr, png_infop info_ptr)
 
       if (png_ptr->buffer_size < png_ptr->current_text_left)
          text_size = png_ptr->buffer_size;
+
       else
          text_size = png_ptr->current_text_left;
+
       png_crc_read(png_ptr, (png_bytep)png_ptr->current_text_ptr, text_size);
       png_ptr->current_text_left -= text_size;
       png_ptr->current_text_ptr += text_size;
@@ -1120,7 +1226,7 @@ png_push_read_tEXt(png_structp png_ptr, png_infop info_ptr)
       key = png_ptr->current_text;
 
       for (text = key; *text; text++)
-         /* empty loop */ ;
+         /* Empty loop */ ;
 
       if (text < key + png_ptr->current_text_size)
          text++;
@@ -1155,7 +1261,7 @@ png_push_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32
    if (!(png_ptr->mode & PNG_HAVE_IHDR) || (png_ptr->mode & PNG_HAVE_IEND))
       {
          png_error(png_ptr, "Out of place zTXt");
-         info_ptr = info_ptr; /* to quiet some compiler warnings */
+         info_ptr = info_ptr; /* To quiet some compiler warnings */
       }
 
 #ifdef PNG_MAX_MALLOC_64K
@@ -1189,8 +1295,10 @@ png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
 
       if (png_ptr->buffer_size < (png_uint_32)png_ptr->current_text_left)
          text_size = png_ptr->buffer_size;
+
       else
          text_size = png_ptr->current_text_left;
+
       png_crc_read(png_ptr, (png_bytep)png_ptr->current_text_ptr, text_size);
       png_ptr->current_text_left -= text_size;
       png_ptr->current_text_ptr += text_size;
@@ -1214,7 +1322,7 @@ png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
       key = png_ptr->current_text;
 
       for (text = key; *text; text++)
-         /* empty loop */ ;
+         /* Empty loop */ ;
 
       /* zTXt can't have zero text */
       if (text >= key + png_ptr->current_text_size)
@@ -1226,7 +1334,7 @@ png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
 
       text++;
 
-      if (*text != PNG_TEXT_COMPRESSION_zTXt) /* check compression byte */
+      if (*text != PNG_TEXT_COMPRESSION_zTXt) /* Check compression byte */
       {
          png_ptr->current_text = NULL;
          png_free(png_ptr, key);
@@ -1265,11 +1373,15 @@ png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
                text = (png_charp)png_malloc(png_ptr,
                      (png_uint_32)(png_ptr->zbuf_size
                      - png_ptr->zstream.avail_out + key_size + 1));
+
                png_memcpy(text + key_size, png_ptr->zbuf,
                   png_ptr->zbuf_size - png_ptr->zstream.avail_out);
+
                png_memcpy(text, key, key_size);
+
                text_size = key_size + png_ptr->zbuf_size -
                   png_ptr->zstream.avail_out;
+
                *(text + text_size) = '\0';
             }
             else
@@ -1280,10 +1392,13 @@ png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
                text = (png_charp)png_malloc(png_ptr, text_size +
                   (png_uint_32)(png_ptr->zbuf_size 
                   - png_ptr->zstream.avail_out + 1));
+
                png_memcpy(text, tmp, text_size);
                png_free(png_ptr, tmp);
+
                png_memcpy(text + text_size, png_ptr->zbuf,
                   png_ptr->zbuf_size - png_ptr->zstream.avail_out);
+
                text_size += png_ptr->zbuf_size - png_ptr->zstream.avail_out;
                *(text + text_size) = '\0';
             }
@@ -1347,7 +1462,7 @@ png_push_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32
    if (!(png_ptr->mode & PNG_HAVE_IHDR) || (png_ptr->mode & PNG_HAVE_IEND))
       {
          png_error(png_ptr, "Out of place iTXt");
-         info_ptr = info_ptr; /* to quiet some compiler warnings */
+         info_ptr = info_ptr; /* To quiet some compiler warnings */
       }
 
 #ifdef PNG_MAX_MALLOC_64K
@@ -1380,8 +1495,10 @@ png_push_read_iTXt(png_structp png_ptr, png_infop info_ptr)
 
       if (png_ptr->buffer_size < png_ptr->current_text_left)
          text_size = png_ptr->buffer_size;
+
       else
          text_size = png_ptr->current_text_left;
+
       png_crc_read(png_ptr, (png_bytep)png_ptr->current_text_ptr, text_size);
       png_ptr->current_text_left -= text_size;
       png_ptr->current_text_ptr += text_size;
@@ -1412,23 +1529,25 @@ png_push_read_iTXt(png_structp png_ptr, png_infop info_ptr)
       key = png_ptr->current_text;
 
       for (lang = key; *lang; lang++)
-         /* empty loop */ ;
+         /* Empty loop */ ;
 
       if (lang < key + png_ptr->current_text_size - 3)
          lang++;
 
       comp_flag = *lang++;
-      lang++;     /* skip comp_type, always zero */
+      lang++;     /* Skip comp_type, always zero */
 
       for (lang_key = lang; *lang_key; lang_key++)
-         /* empty loop */ ;
-      lang_key++;        /* skip NUL separator */
+         /* Empty loop */ ;
+
+      lang_key++;        /* Skip NUL separator */
 
       text=lang_key;
+
       if (lang_key < key + png_ptr->current_text_size - 1)
       {
         for (; *text; text++)
-           /* empty loop */ ;
+           /* Empty loop */ ;
       }
 
       if (text < key + png_ptr->current_text_size)
@@ -1436,6 +1555,7 @@ png_push_read_iTXt(png_structp png_ptr, png_infop info_ptr)
 
       text_ptr = (png_textp)png_malloc(png_ptr,
          (png_uint_32)png_sizeof(png_text));
+
       text_ptr->compression = comp_flag + 2;
       text_ptr->key = key;
       text_ptr->lang = lang;
@@ -1477,7 +1597,7 @@ png_push_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32
 #endif
          png_chunk_error(png_ptr, "unknown critical chunk");
 
-      info_ptr = info_ptr; /* to quiet some compiler warnings */
+      info_ptr = info_ptr; /* To quiet some compiler warnings */
    }
 
 #if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
@@ -1498,23 +1618,28 @@ png_push_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32
         = '\0';
 
       png_ptr->unknown_chunk.size = (png_size_t)length;
+
       if (length == 0)
          png_ptr->unknown_chunk.data = NULL;
+
       else
       {
          png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr,
        (png_uint_32)length);
          png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
       }
+
 #if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
       if (png_ptr->read_user_chunk_fn != NULL)
       {
-         /* callback to user unknown chunk handler */
+         /* Callback to user unknown chunk handler */
          int ret;
          ret = (*(png_ptr->read_user_chunk_fn))
            (png_ptr, &png_ptr->unknown_chunk);
+
          if (ret < 0)
             png_chunk_error(png_ptr, "error in user chunk");
+
          if (ret == 0)
          {
             if (!(png_ptr->chunk_name[0] & 0x20))
@@ -1525,12 +1650,14 @@ png_push_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32
                &png_ptr->unknown_chunk, 1);
          }
       }
+
       else
 #endif
         png_set_unknown_chunks(png_ptr, info_ptr, &png_ptr->unknown_chunk, 1);
       png_free(png_ptr, png_ptr->unknown_chunk.data);
       png_ptr->unknown_chunk.data = NULL;
    }
+
    else
 #endif
       skip=length;
@@ -1567,7 +1694,9 @@ png_progressive_combine_row (png_structp png_ptr,
    PNG_CONST int FARDATA png_pass_dsp_mask[7] =
       {0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff};
 #endif
-   if (png_ptr == NULL) return;
+   if (png_ptr == NULL)
+      return;
+
    if (new_row != NULL)    /* new_row must == png_ptr->row_buf here. */
       png_combine_row(png_ptr, old_row, png_pass_dsp_mask[png_ptr->pass]);
 }
@@ -1577,7 +1706,9 @@ png_set_progressive_read_fn(png_structp png_ptr, png_voidp progressive_ptr,
    png_progressive_info_ptr info_fn, png_progressive_row_ptr row_fn,
    png_progressive_end_ptr end_fn)
 {
-   if (png_ptr == NULL) return;
+   if (png_ptr == NULL)
+      return;
+
    png_ptr->info_fn = info_fn;
    png_ptr->row_fn = row_fn;
    png_ptr->end_fn = end_fn;
@@ -1588,7 +1719,9 @@ png_set_progressive_read_fn(png_structp png_ptr, png_voidp progressive_ptr,
 png_voidp PNGAPI
 png_get_progressive_ptr(png_structp png_ptr)
 {
-   if (png_ptr == NULL) return (NULL);
+   if (png_ptr == NULL)
+      return (NULL);
+
    return png_ptr->io_ptr;
 }
 #endif /* PNG_PROGRESSIVE_READ_SUPPORTED */