Stefan Krah added the comment: People have posted the asm now:
https://mail.python.org/pipermail/python-list/2015-July/693509.html The fmull result appears to be the same. The good gcc versions set the control word to "truncate" and then use fistpl (single rounding with the correct mode): fmull -0x10(%ebp) fnstcw -0x1a(%ebp) movzwl -0x1a(%ebp),%eax mov $0xc,%ah mov %ax,-0x1c(%ebp) fldcw -0x1c(%ebp) fistpl -0x20(%ebp) The bad versions dump the result of fmull to memory, using "round-to-nearest" and *then* attempt to truncate with cvttsd2si, which is too late. fmull 0x18(%esp) fstpl 0x8(%esp) cvttsd2si 0x8(%esp),%eax I suspect that there are passages in various standards that allow both behaviors. ;) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue24546> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
