mirror of https://github.com/python/cpython
bpo-44954: Fix wrong result in float.fromhex corner case (GH-27834)
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@ -1468,6 +1468,20 @@ class HexFloatTestCase(unittest.TestCase):
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self.identical(fromHex('0X1.0000000000001fp0'), 1.0+2*EPS)
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self.identical(fromHex('0x1.00000000000020p0'), 1.0+2*EPS)
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# Regression test for a corner-case bug reported in b.p.o. 44954
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self.identical(fromHex('0x.8p-1074'), 0.0)
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self.identical(fromHex('0x.80p-1074'), 0.0)
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self.identical(fromHex('0x.81p-1074'), TINY)
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self.identical(fromHex('0x8p-1078'), 0.0)
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self.identical(fromHex('0x8.0p-1078'), 0.0)
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self.identical(fromHex('0x8.1p-1078'), TINY)
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self.identical(fromHex('0x80p-1082'), 0.0)
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self.identical(fromHex('0x81p-1082'), TINY)
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self.identical(fromHex('.8p-1074'), 0.0)
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self.identical(fromHex('8p-1078'), 0.0)
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self.identical(fromHex('-.8p-1074'), -0.0)
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self.identical(fromHex('+8p-1078'), 0.0)
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def test_roundtrip(self):
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def roundtrip(x):
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return fromHex(toHex(x))
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@ -0,0 +1,2 @@
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Fixed a corner case bug where the result of ``float.fromhex('0x.8p-1074')``
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was rounded the wrong way.
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@ -1463,8 +1463,8 @@ float_fromhex(PyTypeObject *type, PyObject *string)
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bits lsb, lsb-2, lsb-3, lsb-4, ... is 1. */
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if ((digit & half_eps) != 0) {
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round_up = 0;
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if ((digit & (3*half_eps-1)) != 0 ||
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(half_eps == 8 && (HEX_DIGIT(key_digit+1) & 1) != 0))
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if ((digit & (3*half_eps-1)) != 0 || (half_eps == 8 &&
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key_digit+1 < ndigits && (HEX_DIGIT(key_digit+1) & 1) != 0))
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round_up = 1;
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else
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for (i = key_digit-1; i >= 0; i--)
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