Issue #10337: skip tests of tanh() sign in test_math and test_cmath if tanh()

doesn't preserve the zero sign (if TANH_PRESERVES_ZERO_SIGN define is 0).

Lib/test/cmath_testcases.txt

@@ -1858,11 +1858,14 @@ sinh1052 sinh -inf inf -> inf nan       invalid ignore-real-sign
 -- tanh: Hyperbolic Tangent --
 ------------------------------
 
--- zeros
-tanh0000 tanh 0.0 0.0 -> 0.0 0.0
-tanh0001 tanh 0.0 -0.0 -> 0.0 -0.0
-tanh0002 tanh -0.0 0.0 -> -0.0 0.0
-tanh0003 tanh -0.0 -0.0 -> -0.0 -0.0
+-- Disabled test: replaced by test_math.testTanhSign()
+-- and test_cmath.testTanhSign()
+
+-- -- zeros
+-- tanh0000 tanh 0.0 0.0 -> 0.0 0.0
+-- tanh0001 tanh 0.0 -0.0 -> 0.0 -0.0
+-- tanh0002 tanh -0.0 0.0 -> -0.0 0.0
+-- tanh0003 tanh -0.0 -0.0 -> -0.0 -0.0
 
 -- random inputs
 tanh0004 tanh -21.200500450664993 -1.6970729480342996 -> -1.0 1.9241352344849399e-19

Lib/test/test_cmath.py

@@ -1,8 +1,9 @@
 from test.support import run_unittest
-from test.test_math import parse_testfile, test_file
+from test.test_math import parse_testfile, test_file, requires_IEEE_754
 import unittest
 import cmath, math
 from cmath import phase, polar, rect, pi
+import sysconfig
 
 INF = float('inf')
 NAN = float('nan')
@@ -61,6 +62,12 @@ def setUp(self):
     def tearDown(self):
         self.test_values.close()
 
+    def assertComplexIdentical(self, a, b):
+        """Fail if two complex numbers value or sign is different."""
+        self.assertEqual(a, b)
+        self.assertEqual(math.copysign(1., a.real), math.copysign(1., b.real))
+        self.assertEqual(math.copysign(1., a.imag), math.copysign(1., b.imag))
+
     def rAssertAlmostEqual(self, a, b, rel_err = 2e-15, abs_err = 5e-323,
                            msg=None):
         """Fail if the two floating-point numbers are not almost equal.
@@ -473,6 +480,15 @@ def test_isinf(self):
         self.assertTrue(cmath.isinf(complex(NAN, INF)))
         self.assertTrue(cmath.isinf(complex(INF, NAN)))
 
+    @requires_IEEE_754
+    @unittest.skipIf(sysconfig.get_config_var('TANH_PRESERVES_ZERO_SIGN') == 0,
+                     "system tanh() function doesn't copy the sign")
+    def testTanhSign(self):
+        self.assertComplexIdentical(cmath.tanh(complex(0., .0j)), complex(0., .0j))
+        self.assertComplexIdentical(cmath.tanh(complex(0., -.0j)), complex(0., -.0j))
+        self.assertComplexIdentical(cmath.tanh(complex(-0., .0j)), complex(-0., .0j))
+        self.assertComplexIdentical(cmath.tanh(complex(-0., -.0j)), complex(-0., -.0j))
+
 
 def test_main():
     run_unittest(CMathTests)

Lib/test/test_math.py

@@ -8,6 +8,7 @@
 import sys
 import random
 import struct
+import sysconfig
 
 eps = 1E-05
 NAN = float('nan')
@@ -891,11 +892,15 @@ def testTanh(self):
         self.ftest('tanh(inf)', math.tanh(INF), 1)
         self.ftest('tanh(-inf)', math.tanh(NINF), -1)
         self.assertTrue(math.isnan(math.tanh(NAN)))
+
+    @requires_IEEE_754
+    @unittest.skipIf(sysconfig.get_config_var('TANH_PRESERVES_ZERO_SIGN') == 0,
+                     "system tanh() function doesn't copy the sign")
+    def testTanhSign(self):
         # check that tanh(-0.) == -0. on IEEE 754 systems
-        if float.__getformat__("double").startswith("IEEE"):
-            self.assertEqual(math.tanh(-0.), -0.)
-            self.assertEqual(math.copysign(1., math.tanh(-0.)),
-                             math.copysign(1., -0.))
+        self.assertEqual(math.tanh(-0.), -0.)
+        self.assertEqual(math.copysign(1., math.tanh(-0.)),
+                         math.copysign(1., -0.))
 
     def test_trunc(self):
         self.assertEqual(math.trunc(1), 1)
@@ -1008,8 +1013,7 @@ def test_testfile(self):
                 self.fail(message)
             self.ftest("%s:%s(%r)" % (id, fn, ar), result, er)
 
-    @unittest.skipUnless(float.__getformat__("double").startswith("IEEE"),
-                         "test requires IEEE 754 doubles")
+    @requires_IEEE_754
     def test_mtestfile(self):
         ALLOWED_ERROR = 20  # permitted error, in ulps
         fail_fmt = "{}:{}({!r}): expected {!r}, got {!r}"