add float math functions to standard library

[andrewrk]

Functions:

• fma
• nan
• abs
• exp
• exp2
• loge
• log2
• log10
• sqrt
• cbrt
• hypot
• pow
• sin
• cos
• tan
• asin
• acos
• atan
• atan2
• sinh
• cosh
• tanh
• asinh
• acosh
• atanh
• ceil
• floor
• trunc
• round
• scalbn
• isfinite
• isinf
• isnan
• isnormal
• signbit

Constants:

• e
• pi

There is also a concept of floating point exceptions which libc lets you query after you do a floating point operation. To be considered if we want to support something like that.

[tiehuis]

I'm slightly interested in this. I've had a bit of a look so far. The following are decent references for implementation (most share some common history):

• https://golang.org/src/math/
• https://git.musl-libc.org/cgit/musl/tree/src/math

One question I had was regarding the handling of the multiple float types. libc for example has separate calls for float, double and long doubles in most places. This seems over the top for the moment and the go math library appears to forgo any explicit f32 routines and just implements f64 functions. This suggests at least that the simplistic upcasting approach doesn't have any glaring problems.

[andrewrk]

My plan was to have zig automatically dispatch to the correct floating point function based on the type. You can see an example with the floor function in std/math.zig.

[tiehuis]

Makes sense. I'll use that method when experimenting with this.

[thejoshwolfe]

am i correct in guessing that all of the listed functions are float-in and/or float-out? this would be in contrast to integer math functions like gcd, isprime, or sign (sometimes).

[andrewrk]

Yes I believe these are all float functions, and the result is the same type as the input.

Side note, I think that go ignores f32 and only has f64 because it lacks generics and this was a way around that.

[tiehuis]

Made a repository here for the moment: https://github.com/tiehuis/zig-fmath

[andrewrk]

Wow nice work @tiehuis. I'll have a look at these and try to get some nice test cases going.

[tiehuis]

One thing I was considering regarding test-cases was to just export the functions under their c equivalents and link against the libc-test cases here.

That being said, the differences between how errors are flagged and the rest could make this not completely straightforward and it may be easier just to rewrite these under zig.

[andrewrk]

That's a good idea. Another idea is to port the test cases to zig test. Should be pretty straightforward. If the test files are big they can go in different file that doesn't get installed with the standard library.

[tiehuis]

An initial implementation of this is currently complete here. There are various edge cases that are currently unimplemented and still needs some improvement and tests, but the initial conversion to zig is complete at least.

See tiehuis/zig-fmath#7 for some discussion questions about some improvements.

[andrewrk]

This is an incredibly huge contribution to zig @tiehuis. 🎉

Would you like to become a member of the zig-lang organization and have commit access?