Compile warnings

[Vincent Lefevre]

On 2016-02-06 17:03:34 +0000, Junges, Sebastian wrote:
> Dear developers,
> 
> We are successfully using gmp in several of our projects. Thanks for all the efforts you put into the project.
> I’m fully aware that compilation time warnings are not the same as bugs, however, I still would like to draw your attention to the following three warnings I get during compilation of files including gmp.h.
> They prevent simple usage of -Werror.
> 
> /usr/local/include/gmp.h:2139:345: warning: equality comparison with extraneous parentheses [-Wparentheses-equality]
>   do { mp_size_t __gmp_i; mp_limb_t __gmp_x; __gmp_i = (__gmp_ysize); if (__gmp_i != 0) { if (__gmpn_add_n (__gmp_wp, __gmp_xp, __gmp_yp, __gmp_i)) { do { if (__gmp_i >= (__gmp_xsize)) { (__gmp_c) = 1; goto __gmp_done; } __gmp_x = (__gmp_xp)[__gmp_i]; } while ((((__gmp_wp)[__gmp_i++] = (__gmp_x + 1) & ((~ (static_cast<mp_limb_t> (0))) >> 0)) == 0)); } } if ((__gmp_wp) != (__gmp_xp)) do { mp_size_t __gmp_j; ; for (__gmp_j = (__gmp_i); __gmp_j < (__gmp_xsize); __gmp_j++) (__gmp_wp)[__gmp_j] = (__gmp_xp)[__gmp_j]; } while (0); (__gmp_c) = 0; __gmp_done: ; } while (0);

This one may be impossible to "fix". If I understand correctly, you
can produce such a warning with something like:

#define FOO (a == b)

while (FOO) { ... }

Due to how the C preprocessor works, extraneous parentheses may happen.
Emitting a warning in such a case is a bad idea.

In gmp.h, this probably comes from:

#define __GMPN_ADD(cout, wp, xp, xsize, yp, ysize)              \
  __GMPN_AORS (cout, wp, xp, xsize, yp, ysize, mpn_add_n,       \
               (((wp)[__gmp_i++] = (__gmp_x + 1) & GMP_NUMB_MASK) == 0))

The extraneous parentheses should be useless here if the __GMPN_AORS
macro is correctly written, though they may be regarded as safer.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
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