On Fri, 21 Sep 2012 17:29:13 +0000, Steven D'Aprano wrote: > Python floats can represent exact integer values (e.g. 42.0), but above > a certain value (see below), not all integers can be represented. For > example: > > py> 1e16 == 1e16 + 1 # no such float as 10000000000000001.0 True py> > 1e16 + 3 == 1e16 + 4 # or 10000000000000003.0 True > > So some integers are missing from the floats. For large enough values, > the gap between floats is rather large, and many numbers are missing: > > py> 1e200 + 1e10 == 1e200 True > > The same applies for large enough negative values. > > The question is, what is the largest integer number N such that every > whole number between -N and N inclusive can be represented as a float? > > If my tests are correct, that value is 9007199254740992.0 = 2**53. > > Have I got this right? Is there a way to work out the gap between one > float and the next? > > (I haven't tried to exhaustively check every float because, even at one > nanosecond per number, it will take over 200 days.)
technically this would be implementation dependant, although the other responses are probably accurate for most (if not all) current implementations :-) -- Well, I'm a classic ANAL RETENTIVE!! And I'm looking for a way to VICARIOUSLY experience some reason to LIVE!! -- http://mail.python.org/mailman/listinfo/python-list
