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bpo-39288: Add math.nextafter(x, y) (GH-17937)

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Return the next floating-point value after x towards y.
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Victor Stinner 2020-01-12 02:15:42 +01:00 • committed by GitHub
parent 1b335ae281
commit 100fafcf20
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6 changed files with 140 additions and 1 deletions
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54
Lib/test/test_math.py
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@ -2033,6 +2033,60 @@ class IsCloseTests(unittest.TestCase):
self.assertIs(type(comb(IntSubclass(5), IntSubclass(k))), int)
self.assertIs(type(comb(MyIndexable(5), MyIndexable(k))), int)
def assertEqualSign(self, x, y):
"""Similar to assertEqual(), but compare also the sign.
Function useful to check to signed zero.
"""
self.assertEqual(x, y)
self.assertEqual(math.copysign(1.0, x), math.copysign(1.0, y))
@requires_IEEE_754
def test_nextafter(self):
# around 2^52 and 2^63
self.assertEqual(math.nextafter(4503599627370496.0, -INF),
4503599627370495.5)
self.assertEqual(math.nextafter(4503599627370496.0, INF),
4503599627370497.0)
self.assertEqual(math.nextafter(9223372036854775808.0, 0.0),
9223372036854774784.0)
self.assertEqual(math.nextafter(-9223372036854775808.0, 0.0),
-9223372036854774784.0)
# around 1.0
self.assertEqual(math.nextafter(1.0, -INF),
float.fromhex('0x1.fffffffffffffp-1'))
self.assertEqual(math.nextafter(1.0, INF),
float.fromhex('0x1.0000000000001p+0'))
# x == y: y is returned
self.assertEqual(math.nextafter(2.0, 2.0), 2.0)
self.assertEqualSign(math.nextafter(-0.0, +0.0), +0.0)
self.assertEqualSign(math.nextafter(+0.0, -0.0), -0.0)
# around 0.0
smallest_subnormal = sys.float_info.min * sys.float_info.epsilon
self.assertEqual(math.nextafter(+0.0, INF), smallest_subnormal)
self.assertEqual(math.nextafter(-0.0, INF), smallest_subnormal)
self.assertEqual(math.nextafter(+0.0, -INF), -smallest_subnormal)
self.assertEqual(math.nextafter(-0.0, -INF), -smallest_subnormal)
self.assertEqualSign(math.nextafter(smallest_subnormal, +0.0), +0.0)
self.assertEqualSign(math.nextafter(-smallest_subnormal, +0.0), -0.0)
self.assertEqualSign(math.nextafter(smallest_subnormal, -0.0), +0.0)
self.assertEqualSign(math.nextafter(-smallest_subnormal, -0.0), -0.0)
# around infinity
largest_normal = sys.float_info.max
self.assertEqual(math.nextafter(INF, 0.0), largest_normal)
self.assertEqual(math.nextafter(-INF, 0.0), -largest_normal)
self.assertEqual(math.nextafter(largest_normal, INF), INF)
self.assertEqual(math.nextafter(-largest_normal, -INF), -INF)
# NaN
self.assertTrue(math.isnan(math.nextafter(NAN, 1.0)))
self.assertTrue(math.isnan(math.nextafter(1.0, NAN)))
self.assertTrue(math.isnan(math.nextafter(NAN, NAN)))
def test_main():
from doctest import DocFileSuite