Sources Bugzilla – Bug 6810
tgamma() does not set errno for underflow error
Last modified: 2012-03-01 23:29:18 UTC
tgamma() correctly sets errno and raises an exception for an overflow error.
However, for an underflow error, it only raises an exception -- errno is not
set; errno should be set to ERANGE for this case.
On error, many glibc math functions both set errno and raise an exception
(fetestexcept(3)). For example, the following function all do this: acos(),
asin(), cosh(), sinh(), acosh(), asinh(), exp(), exp2(), ldexp(), log(),
log10(), log2(). However, there is much inconsistency. Some functions raise an
exception, but don't set errno. Some functions set errno for some errors, but
not others. A few set errno, but don't raise an exception. This series of bug
reports documents deviations from what I consider the ideal: all functions
should BOTH set errno AND raise an exception for all errors.
All of these reports relate to tests on glibc 2.8 (as provided by SUSE 11.0).
Created attachment 2882 [details]
Sample runs demonstrating the problem:
$ /tmp/mt_tgamma 1e3
errno == ERANGE
fetestexcept() says: FE_OVERFLOW FE_INEXACT
ERANGE FE_OVERFLOW +inf
$ /tmp/mt_tgamma -- -100000.5
errno == 0
fetestexcept() says: FE_UNDERFLOW FE_INEXACT
0 FE_UNDERFLOW -0
Confirmed for current sources on both x86 and x86_64 - with the addition that on x86_64, the underflow exception for -100000.5 is also missing (it's present on x86).