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Re: MSVC fails to compile floor.c with -fp:strict

From: Bastien ROUCARIES
Subject: Re: MSVC fails to compile floor.c with -fp:strict
Date: Wed, 14 Mar 2012 17:42:39 +0100

On Wed, Mar 14, 2012 at 11:22 AM, Michael Goffioul
<address@hidden> wrote:
> On Wed, Mar 14, 2012 at 9:48 AM, Bruno Haible <address@hidden> wrote:
>> Michael Goffioul wrote:
>>> I encountered a compilation error with MSVC when compiling floor.c in
>>> strict floating-point mode (-fp:strict).
>> Note that the use of -fp:strict also leads to test failures such as
>>  test-hypot.h:41: assertion failed
>>  FAIL: test-hypotl.exe
>> MSVC appears to compile the test code (test-hypotl.c) in a different way,
>> in such a way that a comparison of +Inf with +Inf fails.
>> I'm therefore not sure this option can be recommended.
> Initially I didn't use it, until I noticed a test failure in octave.
> At some point, 2 complex numbers are compared with '<': in octave,
> this is implemented by comparing the modules, then the arguments.
> However, the result of b < a was true while a and b were the same.
> This boiled down to rounding error accumulation in the FPU and the
> only way to avoid it was to use -fp:strict. According to MSVC
> documentation, this is the only way to get IEEE compliance
> (http://msdn.microsoft.com/en-us/library/ms235601(v=vs.100).aspx) and
> this is required in a software like octave.

MSVC is broken for floating point comparaison see for instance

> Michael.

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