On Tue, 29 Nov 2005 14:31:46 GMT, [EMAIL PROTECTED] (Bengt Richter) wrote: > On Mon, 28 Nov 2005 07:58:37 -0800, [EMAIL PROTECTED] (Alex Martelli) wrote:
>> Python's builtin floats compare for exact bit-by-bit equality -- no >> "threshold". You may want to look at the allclose function in the > Does "exact bit-by-bit" mean that > a = <floatexpr> > a == <floatexpr> > is 100% guaranteed? I.e., are there implementations where an > expression value might remain in 80-bit representation in the fpu and > be rounded to 64 bits for assignment to a and then not compare equal > because the second a is a rounded 64-bit value compared to the > regenerated 80-bit value? IIRC, if you consider NaNs, then a == a isn't even guaranteed if a might be a NaN, but that's probably Too Much Information. ;-) There have been (and may well still be) seemingly endless debates about this on comp.std.c (even without the possibility of NaNs, for similar reasons to the one you cite). I don't know if the Lisp and/or IEEE-754 crowds have worked all of this out. Regards, Dan -- Dan Sommers <http://www.tombstonezero.net/dan/> -- http://mail.python.org/mailman/listinfo/python-list
