mini-gmp "bug" missing mpz_fits_sint_p / mpz_fits_uint_p

[Vincent Lefevre]

On 2020-04-20 15:25:54 +0200, Marco Bodrato wrote:
> Ciao,
> 
> Il 2020-04-20 11:08 Vincent Lefevre ha scritto:
> > I think that in general, you should not write code that depends on
> > whether INT_MAX + INT_MIN == 0 or not (the constant INT_MAX + INT_MIN
> > might be useful in some rare cases, but I think that testing whether
> > this constant is 0 or not should be forbidden). This can mean that
> 
> Forbidden? Really! :-D
> 
> Anyway, using the numerical constant INT_MAX + INT_MIN is a good idea.
> 
> What about the following version of the function? :-D
> 
> int
> mpz_fits_sint_p (const mpz_t u)
> {
>   return mpz_cmpabs_ui (u, (unsigned long) INT_MAX + (unsigned long)
> 			(u->_mp_size < 0 ? -(INT_MAX + INT_MIN) : 0)) <= 0;
> }

Here you do not test whether INT_MAX + INT_MIN is 0 or not, so this
is OK. However, after fixing the typo (i -> u),

int
mpz_fits_sint_p (const mpz_t u)
{
  return mpz_cmp_si (u, INT_MAX) <= 0 && mpz_cmp_si (u, INT_MIN) >= 0;
}

is much more readable. And if you don't want 2 function calls,

int
mpz_fits_sint_p (const mpz_t u)
{
  return u->_mp_size < 0 ? mpz_cmp_si (u, INT_MIN) >= 0
                         : mpz_cmp_si (u, INT_MAX) <= 0;
}

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