[libpng16] Imported from libpng-1.6.24beta02.tar

1 files changed, 4 insertions, 2 deletions

diff --git a/pngwutil.c b/pngwutil.c
index 665464be1..c1751fe5a 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -2448,7 +2448,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
       /* Overflow can occur in the calculation, just select the lowest set
        * filter.
        */
-      filter_to_do &= 0U-filter_to_do;
+      filter_to_do &= -filter_to_do;
    }
    else if ((filter_to_do & PNG_FILTER_NONE) != 0 &&
          filter_to_do != PNG_FILTER_NONE)
@@ -2477,7 +2477,9 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
    /* It's the only filter so no testing is needed */
    {
       /* Passing PNG_SIZE_MAX here and below prevents the 'setup' function
-       * breaking out of the loop when lmins is exceeded.
+       * breaking out of the loop when lmins is exceeded. Optimizing
+       * compilers should notice that we don't use the returned sum, and
+       * therefore 'setup' should refrain from calculating and returning "sum".
        */
       (void) png_setup_sub_row(png_ptr, bpp, row_bytes, PNG_SIZE_MAX);
       best_row = png_ptr->try_row;