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Re: Why was the reallocarray function not added to glibc?
On 10/04/2017 07:15, Szabolcs Nagy wrote:
> On 07/04/17 21:47, Paul Eggert wrote:
>> The patch should use gcc builtins (when available) to detect integer overflow instead of trying to do it by
>> hand. You can do this by using the INT_MULTIPLY_OVERFLOW macro of Gnulib, documented here:
>>
>> https://www.gnu.org/software/gnulib/manual/html_node/Integer-Type-Overflow.html
>>
>> The easist way to use that macro is to copy gnulib intprops.h as-is into glibc, and then use "#include
>> <intprops.h>". It need not be a public include file. Here's the current source:
>>
>> http://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/intprops.h
>
> that is not just ugly but looks wrong too (it's
> for signed mul).
>
> the idiomatic unsigned mul overflow check is
>
> if (b && -1/b < a)
> return 0;
> c = a*b;
>
> this can be recognized in the source by humans
> and compilers too (fix the compiler if not) with
> well defined semantics, i see no reason to use
> non-portable built-ins or mountains of macros.
>
I agree, the intprop.s is somewhat convoluted and I would avoid add it
to glibc.