Warnings in GMP.H, and potentially more serious problem
jfoug at cox.net
jfoug at cox.net
Sun Jul 4 19:11:27 CEST 2004
The easiest "fix" to this problem is to change the line (2 lines actually in different #defines) from
return __gmp_l & (-(mp_limb_t) (__gmp_n != 0));
to
return __gmp_l & (~((mp_limb_t) (__gmp_n != 0)));
I am not sure if the code you listed below: return (__gmp_n != 0 ? __gmp_l : 0); would cause conditional execution paths or not, but I image that it does. The code I listed above should not, and if the (__gmp_n != 0) does, then it can be changed to !!_gmp_n as in:
return __gmp_l & (~((mp_limb_t)!!__gmp_n));
Jim.
----- Orignal messages -------
"delta trinity" <deltatrinity at hotmail.com> writes:
>
> [C++ Warning] gmp.h(1595): W8008 Condition is always true
> [C++ Warning] gmp.h(1596): W8041 Negating unsigned value
>
> Those are only warnings, and does not cause the compilation to fail.
They're also a bit over zealous really, but we should be able to avoid
them. I'm looking at something like the following.
unsigned long
mpz_get_ui (mpz_srcptr __gmp_z) __GMP_NOTHROW
{
mp_ptr __gmp_p = __gmp_z->_mp_d;
mp_size_t __gmp_n = __gmp_z->_mp_size;
mp_limb_t __gmp_l = __gmp_p[0];
/* This is a "#if" rather than a plain "if" so as to avoid gcc warnings
about "<< GMP_NUMB_BITS" exceeding the type size, and to avoid Borland
C++ 6.0 warnings about condition always true for something like
"__GMP_ULONG_MAX < GMP_NUMB_MASK". */
#if GMP_NAIL_BITS == 0 || defined (_LONG_LONG_LIMB)
/* limb==long and no nails, or limb==longlong, one limb is enough */
return (__gmp_n != 0 ? __gmp_l : 0);
#else
/* limb==long and nails, need two limbs when available */
__gmp_n = __GMP_ABS (__gmp_n);
if (__gmp_n <= 1)
return (__gmp_n != 0 ? __gmp_l : 0);
else
return __gmp_l + (__gmp_p[1] << GMP_NUMB_BITS);
#endif
}
> Looking at the code, at the second warning, could (__gmp_n != 0) give
> problems if a compiler decide to evaluate the expression to anything
> other than 1.
No, the relational operators always give 1 or 0.
> The warnings themself are seen when I compile C++ console application.
> I tried compiling a C console application and they didn't show.
> Probably the compiler use two different core for C and C++.
Or it's just the nature of c++ to be pedantic, g++ is pickier than gcc
too.
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