On May 22, 6:09 am, Ross Ridge <[EMAIL PROTECTED]> wrote: > Henrique Dante de Almeida <[EMAIL PROTECTED]> wrote: > > > Finally (and the answer is obvious). 387 breaks the standards and > >doesn't use IEEE double precision when requested to do so. > > Actually, the 80387 and the '87 FPU in all other IA-32 processors > do use IEEE 745 double-precision arithmetic when requested to do so.
True. :-/ It seems that it uses a flag to control the precision. So, a conformant implementation would require saving/restoring the flag between calls. No wonder why gcc doesn't try to do this. There are two possible options for python, in that case: - Leave it as it is. The python language states that floating point operations are based on the underlying C implementation. Also, the relative error in this case is around 1e-16, which is smaller than the expected error for IEEE doubles (~2e-16), so the result is non- standard, but acceptable (in the general case, I believe the rounding error could be marginally bigger than the expected error in extreme cases, though). - Use long doubles for archictectures that don't support SSE2 and use SSE2 IEEE doubles for architectures that support it. A third option would be for python to set the x87 precision to double and switch it back to extended precision when calling C code (that would be too much work for nothing). -- http://mail.python.org/mailman/listinfo/python-list
