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Unsigned overflow

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Remove all currently detected cases of unsigned overflow.  Detection is
runtime, so test case dependent.  The changes to pngvalid.c eliminate
spurious and probably invalid tests with one while loop exception.

Apart from that and the change to the dependence on the intended
unsigned overflow in pngtrans.c the changes are limited to altering the
meme for an unsigned 'x' from:

   while (x-- > 0)

to

   for (; x > 0; --x)

This works because, in all cases, the control variable is not used in
the loop.  The 'while' meme was, at one time, warn'ed by GCC so it is
probably a good change, for some weird religious value of good.

Signed-off-by: John Bowler <jbowler@acm.org>
This commit is contained in:
John Bowler
2016-09-30 18:37:22 -07:00
parent 04dab1e82d
commit 319c9852bf
6 changed files with 52 additions and 21 deletions
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8
pngwrite.c
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@@ -1554,7 +1554,7 @@ png_write_image_16bit(png_voidp argument)
*/
row_end = output_row + image->width * (channels+1);
while (y-- > 0)
for (; y > 0; --y)
{
png_const_uint_16p in_ptr = input_row;
png_uint_16p out_ptr = output_row;
@@ -1705,7 +1705,7 @@ png_write_image_8bit(png_voidp argument)
/* Use row_end in place of a loop counter: */
row_end = output_row + image->width * (channels+1);
while (y-- > 0)
for (; y > 0; --y)
{
png_const_uint_16p in_ptr = input_row;
png_bytep out_ptr = output_row;
@@ -1746,7 +1746,7 @@ png_write_image_8bit(png_voidp argument)
*/
png_bytep row_end = output_row + image->width * channels;
while (y-- > 0)
for (; y > 0; --y)
{
png_const_uint_16p in_ptr = input_row;
png_bytep out_ptr = output_row;
@@ -2136,7 +2136,7 @@ png_image_write_main(png_voidp argument)
ptrdiff_t row_bytes = display->row_bytes;
png_uint_32 y = image->height;
while (y-- > 0)
for (; y > 0; --y)
{
png_write_row(png_ptr, row);
row += row_bytes;