floating point inconsistency

Andrew Haley aph@redhat.com
Wed Feb 17 14:50:00 GMT 2010


On 02/17/2010 02:26 PM, Vincent Lefevre wrote:
> On 2010-02-16 15:39:31 +0100, Christoph Groth wrote:
>> Thank you all very much for clarifying this issue.  I am very much
>> surprised that x87 instructions behave differently on AMD and Intel
>> processors but this seems indeed to be the case.
> 
> That's for elementary functions only (e.g. fsincos here). On
> 
>   http://www.vinc17.net/research/testlibm/
> 
> you can see that different platforms give different results.
> Differencies may be due to the OS, the C library and/or the
> hardware.
> 
> Note that on x86_64 machines, sin and cos are correctly rounded
> (this is not proved, but probably true in practice, assuming no
> bugs in the implementation). I wonder why GCC doesn't use these
> functions by default instead of glibc's sincos (which could be
> enabled only with an option like -ffast-math).

Maybe this is a bug.  There is a version of sincos in the IBM Accurate
Mathematical Library but it's not used in this case.

Andrew.



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