Method test_fma_overflow

Lib/test/test_math.py:2746–2777

(self)

        self.assertIsPositiveZero(math.fma(x-y, -(x+y), z))

    def test_fma_overflow(self):
        a = b = float.fromhex('0x1p512')
        c = float.fromhex('0x1p1023')
        # Overflow from multiplication.
        with self.assertRaises(OverflowError):
            math.fma(a, b, 0.0)
        self.assertEqual(math.fma(a, b/2.0, 0.0), c)
        # Overflow from the addition.
        with self.assertRaises(OverflowError):
            math.fma(a, b/2.0, c)
        # No overflow, even though a*b overflows a float.
        self.assertEqual(math.fma(a, b, -c), c)

        # Extreme case: a * b is exactly at the overflow boundary, so the
        # tiniest offset makes a difference between overflow and a finite
        # result.
        a = float.fromhex('0x1.ffffffc000000p+511')
        b = float.fromhex('0x1.0000002000000p+512')
        c = float.fromhex('0x0.0000000000001p-1022')
        with self.assertRaises(OverflowError):
            math.fma(a, b, 0.0)
        with self.assertRaises(OverflowError):
            math.fma(a, b, c)
        self.assertEqual(math.fma(a, b, -c),
                         float.fromhex('0x1.fffffffffffffp+1023'))

        # Another extreme case: here a*b is about as large as possible subject
        # to math.fma(a, b, c) being finite.
        a = float.fromhex('0x1.ae565943785f9p+512')
        b = float.fromhex('0x1.3094665de9db8p+512')
        c = float.fromhex('0x1.fffffffffffffp+1023')
        self.assertEqual(math.fma(a, b, -c), c)

    def test_fma_single_round(self):
        a = float.fromhex('0x1p-50')