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, 13 insertions, 13 deletions

diff --git a/pngwrite.c b/pngwrite.c
index 052a47c57..98bce0e35 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -1536,7 +1536,7 @@ png_write_image_16bit(png_voidp argument)
        display->first_row);
    png_uint_16p output_row = png_voidcast(png_uint_16p, display->local_row);
    png_uint_16p row_end;
-   const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
+   unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
        3 : 1;
    int aindex = 0;
    png_uint_32 y = image->height;
@@ -1573,7 +1573,7 @@ png_write_image_16bit(png_voidp argument)
 
       while (out_ptr < row_end)
       {
-         const png_uint_16 alpha = in_ptr[aindex];
+         png_uint_16 alpha = in_ptr[aindex];
          png_uint_32 reciprocal = 0;
          int c;
 
@@ -1695,7 +1695,7 @@ png_write_image_8bit(png_voidp argument)
        display->first_row);
    png_bytep output_row = png_voidcast(png_bytep, display->local_row);
    png_uint_32 y = image->height;
-   const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
+   unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
        3 : 1;
 
    if ((image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
@@ -1783,25 +1783,25 @@ png_write_image_8bit(png_voidp argument)
 static void
 png_image_set_PLTE(png_image_write_control *display)
 {
-   const png_imagep image = display->image;
+   png_imagep image = display->image;
    const void *cmap = display->colormap;
-   const int entries = image->colormap_entries > 256 ? 256 :
+   int entries = image->colormap_entries > 256 ? 256 :
        (int)image->colormap_entries;
 
    /* NOTE: the caller must check for cmap != NULL and entries != 0 */
-   const png_uint_32 format = image->format;
-   const unsigned int channels = PNG_IMAGE_SAMPLE_CHANNELS(format);
+   png_uint_32 format = image->format;
+   unsigned int channels = PNG_IMAGE_SAMPLE_CHANNELS(format);
 
 #   if defined(PNG_FORMAT_BGR_SUPPORTED) &&\
       defined(PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED)
-      const int afirst = (format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
+      int afirst = (format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
           (format & PNG_FORMAT_FLAG_ALPHA) != 0;
 #   else
 #     define afirst 0
 #   endif
 
 #   ifdef PNG_FORMAT_BGR_SUPPORTED
-      const int bgr = (format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
+      int bgr = (format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
 #   else
 #     define bgr 0
 #   endif
@@ -1951,12 +1951,12 @@ png_image_write_main(png_voidp argument)
     * and total image size to ensure that they are within the system limits.
     */
    {
-      const unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
+      unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
 
       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 (display->row_stride == 0)
             display->row_stride = (png_int_32)/*SAFE*/png_row_stride;
@@ -2052,7 +2052,7 @@ png_image_write_main(png_voidp argument)
     */
    if (write_16bit != 0)
    {
-      const png_uint_16 le = 0x0001;
+      png_uint_16 le = 0x0001;
 
       if ((*(png_const_bytep) & le) != 0)
          png_set_swap(png_ptr);
@@ -2166,7 +2166,7 @@ image_memory_write)(png_structp png_ptr, png_bytep/*const*/ data, size_t size)
 {
    png_image_write_control *display = png_voidcast(png_image_write_control*,
        png_ptr->io_ptr/*backdoor: png_get_io_ptr(png_ptr)*/);
-   const png_alloc_size_t ob = display->output_bytes;
+   png_alloc_size_t ob = display->output_bytes;
 
    /* Check for overflow; this should never happen: */
    if (size <= ((png_alloc_size_t)-1) - ob)