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Issue #15477: Add workaround for log1p(-0.0) on platforms where it's broken.

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This commit is contained in:
Mark Dickinson 2012-08-18 12:24:30 +01:00
parent 31a11902b3
commit 05d79e9abf
4 changed files with 28 additions and 10 deletions
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23
Modules/_math.c
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@ -189,6 +189,27 @@ _Py_expm1(double x)
significant loss of precision that arises from direct evaluation when x is
small. */
#ifdef HAVE_LOG1P
double
_Py_log1p(double x)
{
/* Some platforms supply a log1p function but don't respect the sign of
zero: log1p(-0.0) gives 0.0 instead of the correct result of -0.0.
To save fiddling with configure tests and platform checks, we handle the
special case of zero input directly on all platforms.
*/
if (x == 0.0) {
return x;
}
else {
return log1p(x);
}
}
#else
double
_Py_log1p(double x)
{
@ -230,3 +251,5 @@ _Py_log1p(double x)
return log(1.+x);
}
}
#endif /* ifdef HAVE_LOG1P */