[PATCH] Improve check against integer wraparound in hcreate_r [BZ #18240]

[Florian Weimer]

On 01/26/2016 01:06 AM, Paul Eggert wrote:
> On 01/25/2016 12:09 PM, Florian Weimer wrote:
>> -  while (div * div < number && number % div != 0)
>> +  while (div * (unsigned long long) div < number && number % div != 0)
> 
> Good catch. But better yet, get rid of the '*' so that we needn't worry
> about whether the multiplication overflows. On typical platforms the
> divide instruction that the '%' is already doing will give us the
> information we need, so this is faster anyway. Something like the
> attached (untested) patch.

I looked at the generated assembly on x86-64, and confirm that there's
just one division.  Rest looks good to me, too.

I'm attaching a real patch which also includes the test I wrote (it
still passes, but it really doesn't do anything).

Florian

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