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pngfix: del workround for GCC7.1 -Wstrict-overflow

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Previously pngfix had been made warning-free in GCC7.1 by marking auto
variables (volatile).  This prevented the arithmetic optimizations which
caused warnings from GCC7.1 with higher values -Wstrict-overflow=<n>

GCC has moved on a lot since 7.1 and pngfix.c now compiles with just one
warning using -Wstrict-overflow=5.  The change includes a change to make
this go away by performing the rearrangement GCC was using in the code:

   i == ndigits-1

becomes:

   i+1 == ndigits

i is initialized to ndigits and has been decremented at least once so
this is fine.

Test, configure:

  CFLAGS="-Wall -Wextra -Wno-maybe-uninitialized -Wstrict-overflow=5" \
    ../configure --enable-werror
  make
  make cehck

Test, cmake:

  cmake ..
  make
  make test

Signed-off-by: John Bowler <jbowler@acm.org>
This commit is contained in:
John Bowler 2024-01-15 09:50:24 -08:00
parent 2a23247420
commit 050ce505e4
1 changed files with 5 additions and 18 deletions
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23
contrib/tools/pngfix.c
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@ -1,6 +1,6 @@
/* pngfix.c
*
* Copyright (c) 2014-2017 John Cunningham Bowler
* Copyright (c) 2014-2017,2024 John Cunningham Bowler
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
@ -20,19 +20,6 @@
#define implies(x,y) assert(!(x) || (y))
#ifdef __GNUC__
/* This is used to fix the error:
*
* pngfix.c:
* In function 'zlib_advance':
* pngfix.c:181:13: error: assuming signed overflow does not
* occur when simplifying conditional to constant [-Werror=strict-overflow]
*/
# define FIX_GCC volatile
#else
# define FIX_GCC
#endif
#define PROGRAM_NAME "pngfix"
/* Define the following to use this program against your installed libpng,
@ -218,7 +205,7 @@ uarb_inc(uarb num, int in_digits, png_int_32 add)
* in_digits+1 if add is known to be in the range -65535..65535.
*/
{
FIX_GCC int out_digits = 0;
int out_digits = 0;
while (out_digits < in_digits)
{
@ -263,7 +250,7 @@ uarb_add32(uarb num, int in_digits, png_uint_32 add)
}
static int
uarb_mult_digit(uarb acc, int a_digits, uarb num, FIX_GCC int n_digits,
uarb_mult_digit(uarb acc, int a_digits, uarb num, int n_digits,
png_uint_16 val)
/* Primitive one-digit multiply - 'val' must be 0..65535. Note that this
* primitive is a multiply and accumulate - the result of *num * val is added
@ -336,7 +323,7 @@ uarb_shift(uarb inout, int ndigits, unsigned int right_shift)
* 1..15
*/
{
FIX_GCC int i = ndigits;
int i = ndigits;
png_uint_16 carry = 0;
assert(right_shift >= 1 && right_shift <= 15);
@ -351,7 +338,7 @@ uarb_shift(uarb inout, int ndigits, unsigned int right_shift)
inout[i] = temp;
/* The shift may reduce ndigits */
if (i == ndigits-1 && temp == 0)
if (i+1 == ndigits && temp == 0)
ndigits = i;
}