Re: [Haskell-cafe] Trouble with asinh (c calls with Doubles) in Windows

The problem of asinh should be fixed in the C runtime library, so it should be fixed in mingw, or by using another C library implementation than mingw's. Actually, Microsoft's recent C library (Universal CRT) seems to have better math functions than mingw, so using it might be an option if possible. (cf. https://mail.haskell.org/pipermail/haskell-cafe/2021-April/133931.html https://awson.github.io/ghc-nw/ ) As to why GCC has two different implementations of asinh -- the implementation of math functions that GCC uses for constant folding is MPFR, which is a bit heavy for linking to every program that it compiles. 2021年9月7日(火) 18:01 David James :

Thanks again. I’ve added a note to the issue, and raised a bug against mingw. (And also updated another related one.)

Is the right solution here to get it fixed in mingw? (And would that then be picked up in some future Haskell release?).

I’m also still a bit confused about ming-w64 and GCC (which are all very new to me). Per Wikipedia “Mingw-w64 includes a port of the GNU Compiler Collection (GCC)”. So why does it have two different implementations of asinh? – one for use by GCC (that gives good results), and one that is called at runtime (that gives bad results)?.

Thanks! David.

From: arata, mizuki Sent: 04 September 2021 12:41 To: David James Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Trouble with asinh (c calls with Doubles) in Windows

FloatFnInverses is marked as ‘expect_broken’ on Windows:

https://gitlab.haskell.org/ghc/ghc/-/blob/922c6bc8dd8d089cfe4b90ec2120cb4895...

And there’s a relevant issue: https://gitlab.haskell.org/ghc/ghc/-/issues/15670

Mizuki

2021/09/04 18:46、David James のメール:

Hi - thank you for this. I was unaware of the “constant folding” in GCC (and I’m surprised it works for functions like asinh), but I can see that it explains the difference in behaviour.

So I think this is a (possibly minor) bug that Haskell inherits from mingw-w64. I guess I should raise a GHC issue – though I’m not sure whether it would be best to try to fix within Haskell or within mingw-w64.

Also, I think the FloatFnInverses.hs test doesn’t should be showing as a fail somewhere in the CI testing. (It doesn’t give the expected output when I run it on Windows). Do you know whether/where I can see that? (I don’t know what CI happens or how to view its output).

Thanks again,

David.

From: arata, mizuki Sent: 03 September 2021 13:43 To: David James Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Trouble with asinh (c calls with Doubles) in Windows

Hi David,

If I understand correctly, GHC uses mingw-w64’s libc implementation on Windows. Since mingw-w64’s math functions are not of very good quality, it is likely that asinh returns NaN for a very large input.

As to why `asinh(1.7976931348623157e308)` in CAsinh.c produces (seemingly-correct) 710.4758, it is probably because the C compiler (GCC) uses a different implementation of asinh when doing constant folding. As a note, you may get a different (compile-time computed) result for `asinh(x)` if you set a more aggressive optimization flag.

Mizuki