On a pole error, logb() correctly raises an exception, but does not set errno.
errno should be set to ERANGE.
(Note that log(), log2(), log10() *do* set errno for a pole error)
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 2855 [details]
Sample run showing problem:
$ /tmp/mt_logb 0
errno == 0
fetestexcept() says: FE_DIVBYZERO
0 FE_DIVBYZERO -inf
Confirmed with current sources on both x86 and x86_64.