Merged revisions 81967 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r81967 | mark.dickinson | 2010-06-13 11:50:29 +0100 (Sun, 13 Jun 2010) | 4 lines

  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.
........
This commit is contained in:
Mark Dickinson 2010-06-13 10:52:38 +00:00
parent c6f1396be0
commit bcdf9da265
5 changed files with 67 additions and 6 deletions

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@ -84,6 +84,25 @@ erf0041 erf 1e16 -> 1.0
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 @@ erfc0051 erfc 1e16 -> 0.0
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 --

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@ -1042,6 +1042,15 @@ class MathTests(unittest.TestCase):
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:

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@ -153,6 +153,7 @@ Benjamin Collar
Jeffery Collins
Robert Collins
Paul Colomiets
Geremy Condra
Juan José Conti
Matt Conway
David M. Cooke

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@ -428,6 +428,9 @@ C-API
Library
-------
- Issue #8986: math.erfc was incorrectly raising OverflowError for
values between -27.3 and -30.0 on some platforms.
- Issue #8784: Set tarfile default encoding to 'utf-8' on Windows.
- Issue #8966: If a ctypes structure field is an array of c_char, convert its

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@ -428,8 +428,8 @@ m_lgamma(double x)
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 @@ m_erf_series(double x)
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 @@ m_erf_series(double x)
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 @@ m_erfc_contfrac(double x)
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 */