[Nick Coghlan] > test_pow is failing on the alpha Debian buildbot, complaining that a > negative number can't be raised to a fractional power. Now, to work > around some bugs in platform implementations of math.fpow(), pow() does > its own check to see if the exponent is an integer. > > The way pow() does that check is to try "iw == floor(iw)", so to see why > the exception was being triggered, I put a couple of extra output lines > into the test and got: > > *** Number: 1.2299999999999999e+167 > *** Floor: 1.2299999999999997e+167 > > Given that the magnitude of the exponent significantly exceeds the > precision of an IEEE double, it seems wrong for floor() to be changing > the mantissa like that
It is wrong -- the machine representation of test_pow's 1.23e167 literal is an exact integer on any current box, and the floor of any exact integer is the integer itself. > (and, on my machine, and all of the other buildbots, it doesn't). > > I've added an explicit test for this misbehaviour to test_math so at > least the buildbot gives a clearer indication of what's going wrong, but > I'm not sure what to do with it beyond that. This isn't Python's problem -- a bug report should be opened against the platform C's implementation of floor(), and the test /should/ fail in Python so long as the platform floor() remains broken. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
