[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.