The POSIX.1 specification of ilogb() says: == Domain Error The x argument is zero, NaN, or ±Inf, or the correct value is not representable as an integer. 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 == However, in all of the above cases, errno is not set on error, and in some of the cases, no exceptions is raised. In all cases errno should be set to EDOM and an FE_INVALID exception should be raised. 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 2856 [details] test program Sample runs demonstrating problem. In no case is errno set. For the Inf and -Inf cases, no exception is raised. $ /tmp/mt_ilogb 0 errno == 0 fetestexcept() says: FE_INVALID FE_DIVBYZERO ilogb(0.00000000000000000e+00)=-2147483648 0 FE_DIVBYZERO normal $ /tmp/mt_ilogb nan errno == 0 fetestexcept() says: FE_INVALID ilogb(nan)=-2147483648 0 FE_INVALID normal $ /tmp/mt_ilogb inf errno == 0 fetestexcept() says: ilogb(inf)=2147483647 0 0 normal $ /tmp/mt_ilogb -- -inf errno == 0 fetestexcept() says: ilogb(-inf)=2147483647 0 0 normal
Also, it is worth noting that log(), log2(), log10() do set errno and raise an exception for the 0 and --inf cases.
Confirmed with current sources on x86. On x86_64, none of these cases raise exceptions or set errno at all (whereas on x86 some at least do raise exceptions).
Thanks for the report, this is fixed now in glibc for glibc 2.16 thanks to Adhemerval Zanella .