The POSIX.1 specification of tgamma says: == The value of x is a negative integer, or x is -Inf. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised. == For both -ve integer and -Inf, GNU's tgamma() correctly raises an FE_INVALID exception. However, errno is only correctly set (to EDOM) for the -ve integer case. For -Inf, errno is not set; it shoul dbe set to EDOM. Background: 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 2881 [details] test program Test runs demonstrating the problem: $ /tmp/mt_tgamma -- -1 errno == EDOM fetestexcept() says: FE_INVALID tgamma(-1.00000000000000000e+00)=nan EDOM FE_INVALID nan $ /tmp/mt_tgamma -- -inf errno == 0 fetestexcept() says: FE_INVALID tgamma(-inf)=nan 0 FE_INVALID nan

Confirmed with current sources on both x86 and x86_64.

Fixed for 2.18 by: commit ab2b94613d85ba9edc659bd5e930b9ab1ec8e8a9 Author: Joseph Myers <joseph@codesourcery.com> Date: Fri May 10 11:35:11 2013 +0000 Fix tgamma errno setting on domain error (bug 6809).