I ran into this last night and posted to python-dev before realizing this bug had been raised: http://mail.python.org/pipermail/python-dev/2012-August/121359.html
I'll reproduce it here as I made a few observations that haven't yet been mentioned in this issue:
The Mountain Lion build slave I set up earlier this evening fails on
test_cmath:
======================================================================
FAIL: test_specific_values (test.test_cmath.CMathTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Volumes/bay2/buildslave/cpython/2.7.snakebite-mountainlion-amd64/build/Lib/test/test_cmath.py", line 352, in test_specific_values
msg=error_message)
File "/Volumes/bay2/buildslave/cpython/2.7.snakebite-mountainlion-amd64/build/Lib/test/test_cmath.py", line 94, in rAssertAlmostEqual
'got {!r}'.format(a, b))
AssertionError: atan0000: atan(complex(0.0, 0.0))
Expected: complex(0.0, 0.0)
Received: complex(0.0, -0.0)
Received value insufficiently close to expected value.
Mountain Lion's atan/log1p appear to drop the negative sign when
passed in -0.0, whereas previous versions of OS X didn't:
Mountain Lion:
% ~/log1p-viper
log1p_drops_zero_sign_test:
atan2(log1p(-0.), -1.) != atan2(-0., -1.)
3.14159 vs -3.14159
atan_drops_zero_sign_test:
atan2(-0., 0.): -0.00000
atan2( 0., -0.): 3.14159
atan2(-0., -0.): -3.14159
atan2( 0., 0.): 0.00000
log1p(-0.): 0.00000
log1p( 0.): 0.00000
Lion:
% ./log1p
log1p_drops_zero_sign_test:
atan2(log1p(-0.), -1.) == atan2(-0., -1.)
-3.14159 vs -3.14159
atan_drops_zero_sign_test:
atan2(-0., 0.): -0.00000
atan2( 0., -0.): 3.14159
atan2(-0., -0.): -3.14159
atan2( 0., 0.): 0.00000
log1p(-0.): -0.00000
log1p( 0.): 0.00000
(The C code for that is below.)
configure.ac already has a test for this (it makes mention of AIX
having similar behaviour), and the corresponding sysconfig entry
named 'LOG1P_DROPS_ZERO_SIGN' is already being used on a few tests,
i.e.:
# The algorithm used for atan and atanh makes use of the system
# log1p function; If that system function doesn't respect the sign
# of zero, then atan and atanh will also have difficulties with
# the sign of complex zeros.
@requires_IEEE_754
@unittest.skipIf(sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN'),
"system log1p() function doesn't preserve the sign")
def testAtanSign(self):
for z in complex_zeros:
self.assertComplexIdentical(cmath.atan(z), z)
@requires_IEEE_754
@unittest.skipIf(sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN'),
"system log1p() function doesn't preserve the sign")
def testAtanhSign(self):
for z in complex_zeros:
self.assertComplexIdentical(cmath.atanh(z), z)
Taking a look at cmath_testcases.txt, and we can see this:
-- These are tested in testAtanSign in test_cmath.py
-- atan0000 atan 0.0 0.0 -> 0.0 0.0
-- atan0001 atan 0.0 -0.0 -> 0.0 -0.0
-- atan0002 atan -0.0 0.0 -> -0.0 0.0
-- atan0003 atan -0.0 -0.0 -> -0.0 -0.0
However, a few lines down, those tests crop up again:
-- special values
atan1000 atan -0.0 0.0 -> -0.0 0.0
<snip>
atan1014 atan 0.0 0.0 -> 0.0 0.0
....which is what causes the current test failures. I hacked
test_cmath.py a bit to spit out all the errors it finds after
it's finished parsing the test file (instead of bombing out on
the first one), and it yielded this:
FAIL: test_specific_values (test.test_cmath.CMathTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Volumes/bay2/buildslave/cpython/3.2.snakebite-mountainlion-amd64/build/Lib/test/test_cmath.py", line 446, in test_specific_values
self.fail("\n".join(failures))
AssertionError: atan1000: atan(complex(-0.0, 0.0))
Expected: complex(-0.0, 0.0)
Received: complex(-0.0, -0.0)
Received value insufficiently close to expected value.
atan1014: atan(complex(0.0, 0.0))
Expected: complex(0.0, 0.0)
Received: complex(0.0, -0.0)
Received value insufficiently close to expected value.
atanh0225: atanh(complex(-0.0, 5.6067e-320))
Expected: complex(-0.0, 5.6067e-320)
Received: complex(0.0, 5.6067e-320)
Received value insufficiently close to expected value.
atanh0227: atanh(complex(-0.0, -3.0861101e-316))
Expected: complex(-0.0, -3.0861101e-316)
Received: complex(0.0, -3.0861101e-316)
Received value insufficiently close to expected value.
atanh1024: atanh(complex(-0.0, -0.0))
Expected: complex(-0.0, -0.0)
Received: complex(0.0, -0.0)
Received value insufficiently close to expected value.
atanh1034: atanh(complex(-0.0, 0.0))
Expected: complex(-0.0, 0.0)
Received: complex(0.0, 0.0)
Received value insufficiently close to expected value.
This is the patch I came up with against test_cmath.py:
xenon% hg diff Lib/test/test_cmath.py
diff -r ce49599b9fdf Lib/test/test_cmath.py
--- a/Lib/test/test_cmath.py Thu Aug 16 22:14:43 2012 +0200
+++ b/Lib/test/test_cmath.py Fri Aug 17 07:54:05 2012 +0000
@@ -121,8 +121,10 @@
# if both a and b are zero, check whether they have the same sign
# (in theory there are examples where it would be legitimate for a
# and b to have opposite signs; in practice these hardly ever
- # occur).
- if not a and not b:
+ # occur) -- the exception to this is if we're on a system that drops
+ # the sign on zeros.
+ drops_zero_sign = sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN')
+ if not drops_zero_sign and not a and not b:
if math.copysign(1., a) != math.copysign(1., b):
self.fail(msg or 'zero has wrong sign: expected {!r}, '
'got {!r}'.format(a, b))
With that applied, all the test_cmath tests pass again (without any
changes to the test file).
Thoughts?
Trent.
--
C code for the example earlier:
#include <math.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
printf("\nlog1p_drops_zero_sign_test:\n");
if (atan2(log1p(-0.), -1.) == atan2(-0., -1.))
printf(" atan2(log1p(-0.), -1.) == atan2(-0., -1.)\n");
else
printf(" atan2(log1p(-0.), -1.) != atan2(-0., -1.)\n");
printf(
" %.5f vs %.5f\n",
atan2(log1p(-0.), -1.),
atan2(-0., -1.)
);
printf("\natan_drops_zero_sign_test:\n");
printf(" atan2(-0., 0.): %0.5f\n", atan2(-0., 0.));
printf(" atan2( 0., -0.): %0.5f\n", atan2( 0., -0.));
printf(" atan2(-0., -0.): %0.5f\n", atan2(-0., -0.));
printf(" atan2( 0., 0.): %0.5f\n", atan2( 0., 0.));
printf(" log1p(-0.): %0.5f\n", log1p(-0.));
printf(" log1p( 0.): %0.5f\n", log1p( 0.));
}
/* vim:set ts=8 sw=4 sts=4 tw=78 et: */
After thinking about it a bit longer, I think patching rAssertAlmostEqual is unnecessarily hacky. The problem is that the 'special value' atan tests in the cmath test file shouldn't have any zero tests -- these are handled in testAtanSign, which is what cmath_testcase.txt states:
---------------------------
-- atan: Inverse tangent --
---------------------------
-- zeros
-- These are tested in testAtanSign in test_cmath.py
-- atan0000 atan 0.0 0.0 -> 0.0 0.0
-- atan0001 atan 0.0 -0.0 -> 0.0 -0.0
-- atan0002 atan -0.0 0.0 -> -0.0 0.0
-- atan0003 atan -0.0 -0.0 -> -0.0 -0.0
So, given, that, let's review the affected tests further down in cmath_testcase.txt:
AssertionError: atan1000: atan(complex(-0.0, 0.0))
Expected: complex(-0.0, 0.0)
Received: complex(-0.0, -0.0)
Received value insufficiently close to expected value.
atan1014: atan(complex(0.0, 0.0))
Expected: complex(0.0, 0.0)
Received: complex(0.0, -0.0)
Received value insufficiently close to expected value.
atanh0225: atanh(complex(-0.0, 5.6067e-320))
Expected: complex(-0.0, 5.6067e-320)
Received: complex(0.0, 5.6067e-320)
Received value insufficiently close to expected value.
atanh0227: atanh(complex(-0.0, -3.0861101e-316))
Expected: complex(-0.0, -3.0861101e-316)
Received: complex(0.0, -3.0861101e-316)
Received value insufficiently close to expected value.
atanh1024: atanh(complex(-0.0, -0.0))
Expected: complex(-0.0, -0.0)
Received: complex(0.0, -0.0)
Received value insufficiently close to expected value.
atanh1034: atanh(complex(-0.0, 0.0))
Expected: complex(-0.0, 0.0)
Received: complex(0.0, 0.0)
Received value insufficiently close to expected value.
I propose we remove the faulty zero tests as follows:
% hg diff
diff -r 05274ab06182 Lib/test/cmath_testcases.txt
--- a/Lib/test/cmath_testcases.txt Sat May 05 21:57:17 2012 -0700
+++ b/Lib/test/cmath_testcases.txt Fri Aug 17 18:58:03 2012 +0000
@@ -849,7 +849,6 @@
atan0304 atan -9.9998886718268301e-321 -1.0 -> -0.78539816339744828 -368.76019403576692
-- special values
-atan1000 atan -0.0 0.0 -> -0.0 0.0
atan1001 atan nan 0.0 -> nan 0.0
atan1002 atan -0.0 1.0 -> -0.0 inf divide-by-zero
atan1003 atan -inf 0.0 -> -1.5707963267948966 0.0
@@ -863,7 +862,6 @@
atan1011 atan -2.2999999999999998 nan -> nan nan
atan1012 atan -inf nan -> -1.5707963267948966 0.0 ignore-imag-sign
atan1013 atan nan nan -> nan nan
-atan1014 atan 0.0 0.0 -> 0.0 0.0
atan1015 atan 0.0 1.0 -> 0.0 inf divide-by-zero
atan1016 atan inf 0.0 -> 1.5707963267948966 0.0
atan1017 atan inf 2.2999999999999998 -> 1.5707963267948966 0.0
@@ -873,7 +871,6 @@
atan1021 atan 0.0 nan -> nan nan
atan1022 atan 2.2999999999999998 nan -> nan nan
atan1023 atan inf nan -> 1.5707963267948966 0.0 ignore-imag-sign
-atan1024 atan 0.0 -0.0 -> 0.0 -0.0
atan1025 atan nan -0.0 -> nan -0.0
atan1026 atan 0.0 -1.0 -> 0.0 -inf divide-by-zero
atan1027 atan inf -0.0 -> 1.5707963267948966 -0.0
@@ -883,7 +880,6 @@
atan1031 atan 2.2999999999999998 -inf -> 1.5707963267948966 -0.0
atan1032 atan inf -inf -> 1.5707963267948966 -0.0
atan1033 atan nan -inf -> nan -0.0
-atan1034 atan -0.0 -0.0 -> -0.0 -0.0
atan1035 atan -0.0 -1.0 -> -0.0 -inf divide-by-zero
atan1036 atan -inf -0.0 -> -1.5707963267948966 -0.0
atan1037 atan -inf -2.2999999999999998 -> -1.5707963267948966 -0.0
That leaves us with:
atanh0225: atanh(complex(-0.0, 5.6067e-320))
Expected: complex(-0.0, 5.6067e-320)
Received: complex(0.0, 5.6067e-320)
Received value insufficiently close to expected value.
atanh0227: atanh(complex(-0.0, -3.0861101e-316))
Expected: complex(-0.0, -3.0861101e-316)
Received: complex(0.0, -3.0861101e-316)
Received value insufficiently close to expected value.
Those aren't duplicate tests like the 0.0 -> -0.0 ones, so, how should they be handled? The proposed patch to rAssertAlmostEqual will skip these ones, but perhaps something like this would be more appropriate:
diff -r 12c062dbe746 Lib/test/cmath_testcases.txt
--- a/Lib/test/cmath_testcases.txt Thu Aug 16 22:18:37 2012 +0200
+++ b/Lib/test/cmath_testcases.txt Fri Aug 17 15:37:11 2012 -0400
@@ -849,7 +849,6 @@
atan0304 atan -9.9998886718268301e-321 -1.0 -> -0.78539816339744828 -368.76019403576692
-- special values
-atan1000 atan -0.0 0.0 -> -0.0 0.0
atan1001 atan nan 0.0 -> nan 0.0
atan1002 atan -0.0 1.0 -> -0.0 inf divide-by-zero
atan1003 atan -inf 0.0 -> -1.5707963267948966 0.0
@@ -863,7 +862,6 @@
atan1011 atan -2.2999999999999998 nan -> nan nan
atan1012 atan -inf nan -> -1.5707963267948966 0.0 ignore-imag-sign
atan1013 atan nan nan -> nan nan
-atan1014 atan 0.0 0.0 -> 0.0 0.0
atan1015 atan 0.0 1.0 -> 0.0 inf divide-by-zero
atan1016 atan inf 0.0 -> 1.5707963267948966 0.0
atan1017 atan inf 2.2999999999999998 -> 1.5707963267948966 0.0
@@ -873,7 +871,6 @@
atan1021 atan 0.0 nan -> nan nan
atan1022 atan 2.2999999999999998 nan -> nan nan
atan1023 atan inf nan -> 1.5707963267948966 0.0 ignore-imag-sign
-atan1024 atan 0.0 -0.0 -> 0.0 -0.0
atan1025 atan nan -0.0 -> nan -0.0
atan1026 atan 0.0 -1.0 -> 0.0 -inf divide-by-zero
atan1027 atan inf -0.0 -> 1.5707963267948966 -0.0
@@ -883,7 +880,6 @@
atan1031 atan 2.2999999999999998 -inf -> 1.5707963267948966 -0.0
atan1032 atan inf -inf -> 1.5707963267948966 -0.0
atan1033 atan nan -inf -> nan -0.0
-atan1034 atan -0.0 -0.0 -> -0.0 -0.0
atan1035 atan -0.0 -1.0 -> -0.0 -inf divide-by-zero
atan1036 atan -inf -0.0 -> -1.5707963267948966 -0.0
atan1037 atan -inf -2.2999999999999998 -> -1.5707963267948966 -0.0
@@ -1011,9 +1007,7 @@
atanh0222 atanh -5.9656816081325078e-317 9.9692253555416263e-313 -> -5.9656816081325078e-317 9.9692253555416263e-313
atanh0223 atanh -6.5606671178400239e-313 -2.1680936406357335e-309 -> -6.5606671178400239e-313 -2.1680936406357335e-309
atanh0224 atanh 0.0 2.5230944401820779e-319 -> 0.0 2.5230944401820779e-319
-atanh0225 atanh -0.0 5.6066569490064658e-320 -> -0.0 5.6066569490064658e-320
atanh0226 atanh 0.0 -2.4222487249468377e-317 -> 0.0 -2.4222487249468377e-317
-atanh0227 atanh -0.0 -3.0861101089206037e-316 -> -0.0 -3.0861101089206037e-316
atanh0228 atanh 3.1219222884393986e-310 0.0 -> 3.1219222884393986e-310 0.0
atanh0229 atanh 9.8926337564976196e-309 -0.0 -> 9.8926337564976196e-309 -0.0
atanh0230 atanh -1.5462535092918154e-312 0.0 -> -1.5462535092918154e-312 0.0
@@ -1051,7 +1045,6 @@
atanh1021 atanh nan -0.0 -> nan nan
atanh1022 atanh nan -2.3 -> nan nan
atanh1023 atanh nan -inf -> 0.0 -1.5707963267948966 ignore-real-sign
-atanh1024 atanh -0.0 -0.0 -> -0.0 -0.0
atanh1025 atanh -0.0 nan -> -0.0 nan
atanh1026 atanh -1.0 -0.0 -> -inf -0.0 divide-by-zero
atanh1027 atanh -0.0 -inf -> -0.0 -1.5707963267948966
@@ -1061,7 +1054,6 @@
atanh1031 atanh -inf -2.3 -> -0.0 -1.5707963267948966
atanh1032 atanh -inf -inf -> -0.0 -1.5707963267948966
atanh1033 atanh -inf nan -> -0.0 nan
-atanh1034 atanh -0.0 0.0 -> -0.0 0.0
atanh1035 atanh -1.0 0.0 -> -inf 0.0 divide-by-zero
atanh1036 atanh -0.0 inf -> -0.0 1.5707963267948966
atanh1037 atanh -2.3 inf -> -0.0 1.5707963267948966
diff -r 12c062dbe746 Lib/test/test_cmath.py
--- a/Lib/test/test_cmath.py Thu Aug 16 22:18:37 2012 +0200
+++ b/Lib/test/test_cmath.py Fri Aug 17 15:37:11 2012 -0400
@@ -532,6 +532,36 @@
for z in complex_zeros:
self.assertComplexIdentical(cmath.atanh(z), z)
+ @requires_IEEE_754
+ @unittest.skipIf(sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN'),
+ "system log1p() function doesn't preserve the sign")
+ def testAtanhSignNearZero(self):
+ for z in (-30861101e-316, 5.6067e-320):
+ expected = complex(-0.0, z)
+ actual = cmath.atanh(complex(-0.0, z))
+ error_message = (
+ 'Expected: complex({!r}, {!r})\n'
+ 'Received: complex({!r}, {!r})\n'
+ 'Received value insufficiently close to expected value.'
+ ).format(
+ expected.real,
+ expected.imag,
+ actual.real,
+ actual.imag
+ )
+
+ self.rAssertAlmostEqual(
+ expected.real,
+ actual.real,
+ abs_err=5e-323,
+ msg=error_message,
+ )
+
+ self.rAssertAlmostEqual(
+ expected.imag,
+ actual.imag,
+ msg=error_message,
+ )
def test_main():
run_unittest(CMathTests)
With this patch applied, test_cmath passes on both Mountain Lion and Lion. I've attached this patch as issue15477.patch.
Thoughts? |
➜
