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Date: Wed, 27 Feb 2019 19:00:38 +0300 (MSK)
From: Alexander Monakov <amonakov@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: FE Exception triggered by comparison
On Thu, 28 Feb 2019, Damian McGuckin wrote:
> I tried the code below, I was just shocked.
>
> #include <math.h>
> #include <stdio.h>
>
> main()
> {
> double x = 5.0;
>
> x -= x, x /= x;
> printf("what %s\n", isnan(x) ? "yes" : "no!");
> return(0);
> }
>
> Looking at the assembler, there is a subroutine call to __isnan. Awful!
Hm, no, for x86 with GCC you should not see that: the compiler knows how
to expand isnan efficiently. Are you perhaps on OS X and the 'gcc' command
actually invokes Clang/LLVM? If not, can you show output of 'gcc -v',
command-line flags you used, and the assembly you're seeing?
Thanks.
Alexander
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