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, 2 insertions, 3 deletions

diff --git a/pngwtran.c b/pngwtran.c
index 9ed551eca..49a13c1e9 100644
--- a/pngwtran.c
+++ b/pngwtran.c
@@ -254,8 +254,7 @@ png_do_shift(png_row_infop row_info, png_bytep row,
 
          for (i = 0; i < istop; i++, bp++)
          {
-
-            const unsigned int c = i%channels;
+            unsigned int c = i%channels;
             int j;
             unsigned int v, out;
 
@@ -283,7 +282,7 @@ png_do_shift(png_row_infop row_info, png_bytep row,
 
          for (bp = row, i = 0; i < istop; i++)
          {
-            const unsigned int c = i%channels;
+            unsigned int c = i%channels;
             int j;
             unsigned int value, v;