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

[David James]

Thanks again. I¡¯ve added a note to the issue, and raised a bug<https://sourceforge.net/p/mingw-w64/bugs/916/> against mingw. (And also updated another<https://sourceforge.net/p/mingw-w64/bugs/515/> 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<https://en.wikipedia.org/wiki/Mingw-w64> ¡°Mingw-w64 includes a port of the GNU Compiler Collection (GCC)¡±. So why does it have two different implementations of asinh? ¨C 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<mailto:minorinoki at gmail.com>
Sent: 04 September 2021 12:41
To: David James<mailto:dj112358 at outlook.com>
Cc: haskell-cafe at haskell.org<mailto:haskell-cafe at 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/922c6bc8dd8d089cfe4b90ec2120cb48959ba2b5/testsuite/tests/numeric/should_run/all.T#L44-45
And there¡¯s a relevant issue: https://gitlab.haskell.org/ghc/ghc/-/issues/15670

Mizuki


2021/09/04 18:46¡¢David James <dj112358 at outlook.com<mailto:dj112358 at outlook.com>>¤Î¥á©`¥ë:

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 ¨C 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<https://gitlab.haskell.org/ghc/ghc/-/blob/master/testsuite/tests/numeric/should_run/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<mailto:minorinoki at gmail.com>
Sent: 03 September 2021 13:43
To: David James<mailto:dj112358 at outlook.com>
Cc: haskell-cafe at haskell.org<mailto:haskell-cafe at 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


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