Re: Using the GNU GMP Library for Bignums in Emacs

[Andreas Schwab]

On Apr 23 2018, Helmut Eller <address@hidden> wrote:

> Out of curiousity: what's the quickest way to detect overflow on
> multiplication in ANSI C?  E.g.
>
>   int64_t x, y, result;
>   result = x * y;
>   if (<how to detect overflow?>)

There is no way to detect overflow after the fact because overflow
invokes undefined behaviour.  You need to either check the range
beforehand, or use special builtins offered by the compiler
(eg. __builtin_smul_overflow in GCC).

Andreas.

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Andreas Schwab, address@hidden
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