Including <limits.h> in gmp-impl.h

[Vincent Lefevre]

> --- a/gmp-h.in  Thu Jan 02 12:28:21 2014 +0100
> +++ b/gmp-h.in  Thu Jan 02 13:25:31 2014 +0100
> @@ -437,10 +437,10 @@
>  #define __GMP_MAX(h,i) ((h) > (i) ? (h) : (i))
>  
>  /* __GMP_USHRT_MAX is not "~ (unsigned short) 0" because short is promoted
> -   to int by "~".  */
> +   to int by "~". It still needs to have the promoted type.  */
>  #define __GMP_UINT_MAX   (~ (unsigned) 0)
>  #define __GMP_ULONG_MAX  (~ (unsigned long) 0)
> -#define __GMP_USHRT_MAX  ((unsigned short) ~0)
> +#define __GMP_USHRT_MAX  (0 + (unsigned short) ~0)

Note that if you want to care of non-two's-complement
implementations, you should write:

#define __GMP_USHRT_MAX  (0 + (unsigned short) -1)

I also find this code slightly more readable (since U..._MAX + 1 = 0
by definition, without having to think of the binary representation).

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