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SF bug 705231: Assertion failed, python aborts.

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float_pow():  Don't let the platform pow() raise -1.0 to an integer power
anymore; at least glibc gets it wrong in some cases.  Note that
math.pow() will continue to deliver wrong (but platform-native) results
in such cases.
This commit is contained in:
Tim Peters 2003-05-24 20:18:24 +00:00
parent 0ed39577dd
commit e87568dd9a
3 changed files with 61 additions and 6 deletions
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17
Lib/test/test_pow.py
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@ -101,6 +101,23 @@ class PowTest(unittest.TestCase):
return None
None ** TestRpow() # Won't fail when __rpow__ invoked. SF bug #643260.
def test_bug705231(self):
# -1.0 raised to an integer should never blow up. It did if the
# platform pow() was buggy, and Python didn't worm around it.
eq = self.assertEquals
a = -1.0
eq(pow(a, 1.23e167), 1.0)
eq(pow(a, -1.23e167), 1.0)
for b in range(-10, 11):
eq(pow(a, float(b)), b & 1 and -1.0 or 1.0)
for n in range(0, 100):
fiveto = float(5 ** n)
# For small n, fiveto will be odd. Eventually we run out of
# mantissa bits, though, and thereafer fiveto will be even.
expected = fiveto % 2.0 and -1.0 or 1.0
eq(pow(a, fiveto), expected)
eq(pow(a, -fiveto), expected)
eq(expected, 1.0) # else we didn't push fiveto to evenness
def test_main():
test.test_support.run_unittest(PowTest)