missing gamma function when built against musl

[notwa]

more fun times with detecting the existence of this function…

this issue prevents the math module from being imported — but let it be known that, after omitting the gamma function, all of kuroko's tests pass with musl! I threw together a Dockerfile running Alpine Linux for testing purposes.

note that musl does implement lgamma (and tgamma), but not gamma. infamously, musl does not define any macros for detection. however, we can exploit a leaked #define from math.h that's existed since 2012.

#ifndef __NEED_double_t
MATH_ONE(gamma)
#endif

/* snip */

#ifndef __NEED_double_t
    KRK_DOC(bind(gamma),
        "@brief Calculates the gamma of the input.\n"
        "@arguments x");
#endif

I did a quick google search to see if any non-musl code is defining __NEED_double_t. it seems that all the results are either forks of musl, or LLVM defining __need_double_t (all lowercase), so I don't think there'll be conflicts with other libc's.

at least, that's my suggestion. I'll leave the final implementation up to you.

[klange]

I was curious what CPython was doing with this mess and apparently it has in-house implementations for a handful of the "weirder" math functions - including gamma (and apparently the reason gamma is missing from Musl is because no one can agree on what function it's actually supposed to implement, so it was dropped from standards considerations).

[notwa]

it's certainly an option to omit the binding altogether. I'm fine with whatever.

[klange]

I dropped math.gamma and have math.lgamma and math.tgamma bound to their libc counterparts, for consistency with the rest of the math module. For things that expect math.gamma (eg., ported Python code), math.gamma = math.tgamma should suffice, and I could bind that alias but have opted not to for now.

I was able to use musl-gcc to build against musl without issue and passed the test suite.

[klange]

Following the CPython approach, when I replace the stubbed versions of these functions in ToaruOS, the tgamma implementation can be included in Kuroko, but for now it seems all of the real-world targets have at least lgamma and tgamma these days.