Fortran90 with +Ofltacc flag on Itanium2 and PA-RISC

[Vefa Kucukboyaci]

Hi,
Few months ago, I compiled a large Fortran code on an Itanium2 machine with HP-UX11.23 / F90 V2.8 using +O3 optimization and +Ofltacc flag, which yielded the exact same numerical results as the version compiled with the -debug version. This was very good news, since we then had a fast running code which produced consistent results as the debug version.

Then, we moved to a new PA-RISC machine running HP-UX11.11 / F90 V2.8.2. The same code compiled with the same options (+O3 +Ofltacc) does not show the same behavior now.

I was wondering if this is an expected behavior, if there is any way to duplicate the same kind of floating-point consistency between the debug and optimized versions of the code on the PA-RISC platform running HP-UX11.11 / F90 V2.8.2.

I'd aprreciate your help/suggestions.

Sincerely,
Vefa Kucukboyaci

[Zygmunt Krawczyk]

Hi,

the accuracy of Itanium2 is better than PA-RISC. Using +Ofltacc on both processors leads to different results. Read about the accuracy of libm on HP-UX/Itanium2:

"The Libm Library and Floating-Point Arithmetic
in HP-UX for Itanium®-Based Systems"
http://h21007.www2.hp.com/dspp/files/unprotected/Itanium/FP_White_Paper_v3.pdf

Regards,
Zygmu