Foating point: tracking change in between gcc 4.4.7 and gcc 4.9.2

Andrew Haley aph@redhat.com
Thu Dec 10 14:30:00 GMT 2015


On 12/10/2015 02:26 PM, Mathieu Malaterre wrote:
> On Thu, Dec 10, 2015 at 12:08 PM, Mathieu Malaterre
> <mathieu.malaterre@gmail.com> wrote:
>>
>> I am trying to track a change in behavior in between gcc 4.4.7
>> (CentOS/x86_64) and gcc 4.9.2 (fedora/x86_64). The result of a complex
>> computation (floating point involved) is slightly different in between
>> those two.
>>
>> Does anyone knows if there was a major change in floating point
>> computation of std::log, std::pow, std::ceil, std::sqrt or std::exp in
>> between those versions? My input is a raw binary (no ASCII parsing
>> involved anywhere in the code). I've compiled code in debug on both
>> side (only option -g is used nothing else).
>>
>> Sorry if this is very broad, I need pointer to get started.
> 
> Just for reference. I've scp'ed the executable file from CentOS over
> my fedora installation and it runs as expected. So the issue is within
> one of the system lib on CentOS (libc/libm/libstdc++6 ?)

So probably not GCC, then.  I'm guessing this is actually glibc.

Surely, though, minor differences are not unexpected?

Andrew.



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