[Python-checkins] r81967 - in python/trunk: Lib/test/math_testcases.txt Lib/test/test_math.py Misc/ACKS Misc/NEWS Modules/mathmodule.c
mark.dickinson
python-checkins at python.org
Sun Jun 13 12:50:30 CEST 2010
Author: mark.dickinson
Date: Sun Jun 13 12:50:29 2010
New Revision: 81967
Log:
Issue #8986: erfc was raising OverflowError on Linux for arguments in
the (approximate) range (-27.3, 30.0), as a result of an escaped errno
value.
Modified:
python/trunk/Lib/test/math_testcases.txt
python/trunk/Lib/test/test_math.py
python/trunk/Misc/ACKS
python/trunk/Misc/NEWS
python/trunk/Modules/mathmodule.c
Modified: python/trunk/Lib/test/math_testcases.txt
==============================================================================
--- python/trunk/Lib/test/math_testcases.txt (original)
+++ python/trunk/Lib/test/math_testcases.txt Sun Jun 13 12:50:29 2010
@@ -84,6 +84,25 @@
erf0042 erf -1e150 -> -1.0
erf0043 erf 1.7e308 -> 1.0
+-- Issue 8986: inputs x with exp(-x*x) near the underflow threshold
+-- incorrectly signalled overflow on some platforms.
+erf0100 erf 26.2 -> 1.0
+erf0101 erf 26.4 -> 1.0
+erf0102 erf 26.6 -> 1.0
+erf0103 erf 26.8 -> 1.0
+erf0104 erf 27.0 -> 1.0
+erf0105 erf 27.2 -> 1.0
+erf0106 erf 27.4 -> 1.0
+erf0107 erf 27.6 -> 1.0
+
+erf0110 erf -26.2 -> -1.0
+erf0111 erf -26.4 -> -1.0
+erf0112 erf -26.6 -> -1.0
+erf0113 erf -26.8 -> -1.0
+erf0114 erf -27.0 -> -1.0
+erf0115 erf -27.2 -> -1.0
+erf0116 erf -27.4 -> -1.0
+erf0117 erf -27.6 -> -1.0
----------------------------------------
-- erfc: complementary error function --
@@ -127,6 +146,25 @@
erfc0052 erfc -1e150 -> 2.0
erfc0053 erfc 1.7e308 -> 0.0
+-- Issue 8986: inputs x with exp(-x*x) near the underflow threshold
+-- incorrectly signalled overflow on some platforms.
+erfc0100 erfc 26.2 -> 1.6432507924389461e-300
+erfc0101 erfc 26.4 -> 4.4017768588035426e-305
+erfc0102 erfc 26.6 -> 1.0885125885442269e-309
+erfc0103 erfc 26.8 -> 2.4849621571966629e-314
+erfc0104 erfc 27.0 -> 5.2370464393526292e-319
+erfc0105 erfc 27.2 -> 9.8813129168249309e-324
+erfc0106 erfc 27.4 -> 0.0
+erfc0107 erfc 27.6 -> 0.0
+
+erfc0110 erfc -26.2 -> 2.0
+erfc0111 erfc -26.4 -> 2.0
+erfc0112 erfc -26.6 -> 2.0
+erfc0113 erfc -26.8 -> 2.0
+erfc0114 erfc -27.0 -> 2.0
+erfc0115 erfc -27.2 -> 2.0
+erfc0116 erfc -27.4 -> 2.0
+erfc0117 erfc -27.6 -> 2.0
---------------------------------------------------------
-- lgamma: log of absolute value of the gamma function --
Modified: python/trunk/Lib/test/test_math.py
==============================================================================
--- python/trunk/Lib/test/test_math.py (original)
+++ python/trunk/Lib/test/test_math.py Sun Jun 13 12:50:29 2010
@@ -996,6 +996,15 @@
accuracy_failure = acc_check(expected, got,
rel_err = 5e-15,
abs_err = 5e-15)
+ elif fn == 'erfc':
+ # erfc has less-than-ideal accuracy for large
+ # arguments (x ~ 25 or so), mainly due to the
+ # error involved in computing exp(-x*x).
+ #
+ # XXX Would be better to weaken this test only
+ # for large x, instead of for all x.
+ accuracy_failure = ulps_check(expected, got, 2000)
+
else:
accuracy_failure = ulps_check(expected, got, 20)
if accuracy_failure is None:
Modified: python/trunk/Misc/ACKS
==============================================================================
--- python/trunk/Misc/ACKS (original)
+++ python/trunk/Misc/ACKS Sun Jun 13 12:50:29 2010
@@ -151,6 +151,7 @@
Jeffery Collins
Robert Collins
Paul Colomiets
+Geremy Condra
Juan José Conti
Matt Conway
David M. Cooke
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS (original)
+++ python/trunk/Misc/NEWS Sun Jun 13 12:50:29 2010
@@ -25,6 +25,10 @@
Library
-------
+
+- Issue #8986: math.erfc was incorrectly raising OverflowError for
+ values between -27.3 and -30.0 on some platforms.
+
- Issue #8924: logging: Improved error handling for Unicode in exception text.
- Issue #8948: cleanup functions and class / module setups and teardowns are
Modified: python/trunk/Modules/mathmodule.c
==============================================================================
--- python/trunk/Modules/mathmodule.c (original)
+++ python/trunk/Modules/mathmodule.c Sun Jun 13 12:50:29 2010
@@ -428,8 +428,8 @@
static double
m_erf_series(double x)
{
- double x2, acc, fk;
- int i;
+ double x2, acc, fk, result;
+ int i, saved_errno;
x2 = x * x;
acc = 0.0;
@@ -438,7 +438,12 @@
acc = 2.0 + x2 * acc / fk;
fk -= 1.0;
}
- return acc * x * exp(-x2) / sqrtpi;
+ /* Make sure the exp call doesn't affect errno;
+ see m_erfc_contfrac for more. */
+ saved_errno = errno;
+ result = acc * x * exp(-x2) / sqrtpi;
+ errno = saved_errno;
+ return result;
}
/*
@@ -453,8 +458,8 @@
static double
m_erfc_contfrac(double x)
{
- double x2, a, da, p, p_last, q, q_last, b;
- int i;
+ double x2, a, da, p, p_last, q, q_last, b, result;
+ int i, saved_errno;
if (x >= ERFC_CONTFRAC_CUTOFF)
return 0.0;
@@ -472,7 +477,12 @@
temp = p; p = b*p - a*p_last; p_last = temp;
temp = q; q = b*q - a*q_last; q_last = temp;
}
- return p / q * x * exp(-x2) / sqrtpi;
+ /* Issue #8986: On some platforms, exp sets errno on underflow to zero;
+ save the current errno value so that we can restore it later. */
+ saved_errno = errno;
+ result = p / q * x * exp(-x2) / sqrtpi;
+ errno = saved_errno;
+ return result;
}
/* Error function erf(x), for general x */
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