diff options
Diffstat (limited to 'Lib/test/test_pow.py')
| -rw-r--r-- | Lib/test/test_pow.py | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Lib/test/test_pow.py b/Lib/test/test_pow.py index cac1ae5..660ff80 100644 --- a/Lib/test/test_pow.py +++ b/Lib/test/test_pow.py @@ -1,3 +1,4 @@ +import math import unittest class PowTest(unittest.TestCase): @@ -119,5 +120,30 @@ class PowTest(unittest.TestCase): eq(pow(a, -fiveto), expected) eq(expected, 1.0) # else we didn't push fiveto to evenness + def test_negative_exponent(self): + for a in range(-50, 50): + for m in range(-50, 50): + with self.subTest(a=a, m=m): + if m != 0 and math.gcd(a, m) == 1: + # Exponent -1 should give an inverse, with the + # same sign as m. + inv = pow(a, -1, m) + self.assertEqual(inv, inv % m) + self.assertEqual((inv * a - 1) % m, 0) + + # Larger exponents + self.assertEqual(pow(a, -2, m), pow(inv, 2, m)) + self.assertEqual(pow(a, -3, m), pow(inv, 3, m)) + self.assertEqual(pow(a, -1001, m), pow(inv, 1001, m)) + + else: + with self.assertRaises(ValueError): + pow(a, -1, m) + with self.assertRaises(ValueError): + pow(a, -2, m) + with self.assertRaises(ValueError): + pow(a, -1001, m) + + if __name__ == "__main__": unittest.main() |