Remove top-level const from function-scope variables

As per the const correctness rules, top-level const-ness of data
in automatic scopes does not propagate outside of these scopes
(unlike const-ness at lower levels, such as pointers to const data).

Previously, const was used liberally, but inconsistently across the
libpng codebase. Using const wherever applicable is not incorrect.
However, _consistent_ use of const is difficult to maintain in such
conditions.

In conclusion, we shall continue to use const only where doing so is
strictly necessary:

1. If a function guarantees that it will not modify an argument
   passed by pointer, the corresponding function parameter should be
   a pointer-to-const (const T *).

2. Static data should not be modified, therefore it should be const.

Reference:
Google C++ Style Guide
https://google.github.io/styleguide/cppguide.html#Use_of_const

1 files changed, 12 insertions, 12 deletions

diff --git a/pngread.c b/pngread.c
index 9c477c1bf..f8e762196 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1758,9 +1758,9 @@ png_create_colormap_entry(png_image_read_control *display,
     png_uint_32 alpha, int encoding)
 {
    png_imagep image = display->image;
-   const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
+   int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
        P_LINEAR : P_sRGB;
-   const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
+   int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
        (red != green || green != blue);
 
    if (ip > 255)
@@ -1869,13 +1869,13 @@ png_create_colormap_entry(png_image_read_control *display,
    /* Store the value. */
    {
 #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
-         const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
+         int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
             (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
 #     else
 #        define afirst 0
 #     endif
 #     ifdef PNG_FORMAT_BGR_SUPPORTED
-         const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
+         int bgr = (image->format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
 #     else
 #        define bgr 0
 #     endif
@@ -2085,11 +2085,11 @@ png_image_read_colormap(png_voidp argument)
 {
    png_image_read_control *display =
       png_voidcast(png_image_read_control*, argument);
-   const png_imagep image = display->image;
+   png_imagep image = display->image;
 
-   const png_structrp png_ptr = image->opaque->png_ptr;
-   const png_uint_32 output_format = image->format;
-   const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
+   png_structrp png_ptr = image->opaque->png_ptr;
+   png_uint_32 output_format = image->format;
+   int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
       P_LINEAR : P_sRGB;
 
    unsigned int cmap_entries;
@@ -2802,7 +2802,7 @@ png_image_read_colormap(png_voidp argument)
             unsigned int num_trans = png_ptr->num_trans;
             png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
             png_const_colorp colormap = png_ptr->palette;
-            const int do_background = trans != NULL &&
+            int do_background = trans != NULL &&
                (output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
             unsigned int i;
 
@@ -3946,7 +3946,7 @@ png_image_read_direct(png_voidp argument)
        */
       if (linear != 0)
       {
-         const png_uint_16 le = 0x0001;
+         png_uint_16 le = 0x0001;
 
          if ((*(png_const_bytep) & le) != 0)
             png_set_swap(png_ptr);
@@ -4108,7 +4108,7 @@ png_image_finish_read(png_imagep image, png_const_colorp background,
        * original PNG format because it may not occur in the output PNG format
        * and libpng deals with the issues of reading the original.
        */
-      const unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
+      unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
 
       /* The following checks just the 'row_stride' calculation to ensure it
        * fits in a signed 32-bit value.  Because channels/components can be
@@ -4119,7 +4119,7 @@ png_image_finish_read(png_imagep image, png_const_colorp background,
       if (image->width <= 0x7fffffffU/channels) /* no overflow */
       {
          png_uint_32 check;
-         const png_uint_32 png_row_stride = image->width * channels;
+         png_uint_32 png_row_stride = image->width * channels;
 
          if (row_stride == 0)
             row_stride = (png_int_32)/*SAFE*/png_row_stride;