Pierre Haessig <pierre.haessig <at> crans.org> writes:
Hi,
Le 29/02/2012 16:22, Paweł Biernat a écrit :
Is there any way to interact with Fortran's real(16) (supported by gcc and Intel's ifort) data type from numpy? By real(16) I mean the binary128 type as in IEEE 754. (In C this data type is experimentally supported as __float128 (gcc) and _Quad (Intel's icc).) I googled a bit this "__float128". It seems a fairly new addition (GCC 4.6, released March 2011). The related point in the changelog [1] is :
"GCC now ships with the LGPL-licensed libquadmath library, which provides quad-precision mathematical functions for targets with a __float128 datatype. __float128 is available for targets on 32-bit x86, x86-64 and Itanium architectures. The libquadmath library is automatically built on such targets when building the Fortran compiler."
It seems this __float128 is newcomer in the "picture of data types" that Matthew just mentioned. As David says, arithmetic with such a 128 bits data type is probably not "hardwired" in most processors (I mean Intel & friends) which are limited to 80 bits ("long doubles") so it may be a bit slow. However, this GCC implementation with libquadmath seems to create some level of abstraction. Maybe this is one acceptably good way for a real "IEEE float 128" dtype in numpy ?
Best, Pierre
[1] http://gcc.gnu.org/gcc-4.6/changes.html
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Intel also has its own implementation of binary128, although not well documented (as you said, it's software emulated, but still quite fast): http://software.intel.com/sites/products/documentation/hpc/compilerpro/en-us... The documentation is for Fortran's real(16), but I belive the same holds for _Quad type in C. My naive question is, is there a way to recompile numpy with "long double" (or just "float128") replaced with "_Quad" or "__float128"? There are at least two compilers that support the respective data types, so this should be doable. I tested interoperability of binary128 with Fortran and C (using gcc and Intel's compilers) and it works like a charm. The only problem that comes to my mind is i/o, because there is no printf format for _Quad or __float128 and fortran routines have to be used to do all i/o. Paweł