Re^2: [C Question] Determine if gcc provides erfl() function

feature_test_macros is where it's at

I take it this means that erfl() is available if either:
a) the "-std=c99" flag is set; or
b) "_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L" is true.

And, if neither of those 2 conditions is met, then erfl() is unavailable.

Is that the correct way to read it ?

Update: If I #define _BSD_SOURCE at the beginning of LongDouble.xs, does this necessarily mean that erfl() is made available on these problem BSD systems ?

Cheers,
Rob

Comment on Re^2: [C Question] Determine if gcc provides erfl() function

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Re^3: [C Question] Determine if gcc provides erfl() function by Anonymous Monk on May 29, 2015 at 04:21 UTC
Negative. On Linux/glibc, normally the _BSD_SOURCE, _SVID_SOURCE, _POSIX_SOURCE are on by default. See `/usr/include/features.h`. On ~BSD, some long double variants may be missing, or implemented as wrappers to a standard double function (with precision loss). Google around (for manpages and discussions). E.g. `erfl()` appears on FreeBSD 10.1 manpages, but not on 10.0. And no `powl()`. The `sinhl/coshl/tanhl` may be wrappers. I started up a decade-old FreeBSD 6.0 install; looking in libm.a (and libc.a), there is no erfl. The gcc-3.4.4 recognizes `__builtin_erfl()`, but this just defers to system erfl, and it fails to link. So, you're out of luck. Furthermore, (some) tests for availability ought to verify the precision, too.	[reply] [d/l] [select]
Re^3: [C Question] Determine if gcc provides erfl() function by RichardK (Parson) on May 29, 2015 at 09:26 UTC
The man page for feature_test_macros has lots of details on how to use these, and the info page has even more. But the easiest way is to set the compiler command line option -std=c99 to ensure that everything (compiler/libc) complies with the C99 standard.	[reply]
Re^4: [C Question] Determine if gcc provides erfl() function by Anonymous Monk on May 29, 2015 at 20:15 UTC
While those functions are, indeed, a normative part of ISO C99 standard, it unfortunately does not follow that passing an option to gcc might cause a fully compliant environment to magically spring into existence. OP is concerned about BSD systems; a reference to glibc manpages is simply misguided.	[reply]