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bpo-39396: Fix math.nextafter(-0.0, +0.0) on AIX 7.1 #18094

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Merged
vstinner merged 1 commit into from
Jan 21, 2020
Merged

bpo-39396: Fix math.nextafter(-0.0, +0.0) on AIX 7.1 #18094

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154 changes: 77 additions & 77 deletions Lib/test/test_math.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1752,6 +1752,83 @@ def assertIsNaN(self, value):
if not math.isnan(value):
self.fail("Expected a NaN, got {!r}.".format(value))

def assertEqualSign(self, x, y):
"""Similar to assertEqual(), but compare also the sign.

Function useful to compare signed zeros.
"""
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)))

@requires_IEEE_754
def test_ulp(self):
self.assertEqual(math.ulp(1.0), sys.float_info.epsilon)
# use int ** int rather than float ** int to not rely on pow() accuracy
self.assertEqual(math.ulp(2 ** 52), 1.0)
self.assertEqual(math.ulp(2 ** 53), 2.0)
self.assertEqual(math.ulp(2 ** 64), 4096.0)

# min and max
self.assertEqual(math.ulp(0.0),
sys.float_info.min * sys.float_info.epsilon)
self.assertEqual(math.ulp(FLOAT_MAX),
FLOAT_MAX - math.nextafter(FLOAT_MAX, -INF))

# special cases
self.assertEqual(math.ulp(INF), INF)
self.assertTrue(math.isnan(math.ulp(math.nan)))

# negative number: ulp(-x) == ulp(x)
for x in (0.0, 1.0, 2 ** 52, 2 ** 64, INF):
with self.subTest(x=x):
self.assertEqual(math.ulp(-x), math.ulp(x))


class IsCloseTests(unittest.TestCase):
isclose = math.isclose # subclasses should override this
Expand Down Expand Up @@ -2009,83 +2086,6 @@ def testComb(self):
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 compare signed zeros.
"""
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)))

@requires_IEEE_754
def test_ulp(self):
self.assertEqual(math.ulp(1.0), sys.float_info.epsilon)
# use int ** int rather than float ** int to not rely on pow() accuracy
self.assertEqual(math.ulp(2 ** 52), 1.0)
self.assertEqual(math.ulp(2 ** 53), 2.0)
self.assertEqual(math.ulp(2 ** 64), 4096.0)

# min and max
self.assertEqual(math.ulp(0.0),
sys.float_info.min * sys.float_info.epsilon)
self.assertEqual(math.ulp(FLOAT_MAX),
FLOAT_MAX - math.nextafter(FLOAT_MAX, -INF))

# special cases
self.assertEqual(math.ulp(INF), INF)
self.assertTrue(math.isnan(math.ulp(math.nan)))

# negative number: ulp(-x) == ulp(x)
for x in (0.0, 1.0, 2 ** 52, 2 ** 64, INF):
with self.subTest(x=x):
self.assertEqual(math.ulp(-x), math.ulp(x))


def test_main():
from doctest import DocFileSuite
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-01-21-09-00-42.bpo-39396.6UXQXE.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix ``math.nextafter(-0.0, +0.0)`` on AIX 7.1.
10 changes: 8 additions & 2 deletions Modules/mathmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3287,8 +3287,14 @@ static PyObject *
math_nextafter_impl(PyObject *module, double x, double y)
/*[clinic end generated code: output=750c8266c1c540ce input=02b2d50cd1d9f9b6]*/
{
double f = nextafter(x, y);
return PyFloat_FromDouble(f);
#if defined(_AIX)
if (x == y) {
/* On AIX 7.1, libm nextafter(-0.0, +0.0) returns -0.0.
Bug fixed in bos.adt.libm 7.2.2.0 by APAR IV95512. */
return PyFloat_FromDouble(y);
}
#endif
return PyFloat_FromDouble(nextafter(x, y));
}


Expand Down