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Groups > comp.lang.c++ > #121722
| From | Michael S <already5chosen@yahoo.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: a MSVC and glibc-compatible fmod() |
| Date | 2025-02-26 14:27 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <20250226142721.0000375b@yahoo.com> (permalink) |
| References | (10 earlier) <vpkoik$22379$1@raubtier-asyl.eternal-september.org> <20250225191715.00001a55@yahoo.com> <vpl0bu$247fb$1@raubtier-asyl.eternal-september.org> <20250226003549.0000251b@yahoo.com> <vpmik1$2frhi$1@dont-email.me> |
On Wed, 26 Feb 2025 08:16:01 -0000 (UTC)
Muttley@DastardlyHQ.org wrote:
> On Wed, 26 Feb 2025 00:36:19 +0200
> Michael S <already5chosen@yahoo.com> wibbled:
> >Here is an example of the program that prints 250508 on Intel Haswell
> >CPU, but prints 0 on Intel Ivy Bridge.
> >Compiled as 'cl -O1 -W4 -MD fma_tst0.c'.
> >
> >#include <stdio.h>
> >#include <stdlib.h>
> >#include <math.h>
> >
> >static
> >unsigned long long rnd(void)
> >{
> > unsigned long long x = 0;
> > for (int i = 0; i < 5; ++i)
> > x = (x << 15) + (rand() & 0x7FFF);
> > return x;
> >}
> >
> >int main(void)
> >{
> > srand(1);
> > int n = 0;
> > for (int i = 0; i < 1000000; ++i) {
> > double x = rnd() * 0x1p-64;
> > double y = rnd() * 0x1p-64;
> > double z = rnd() * 0x1p-114;
> > double r1 = x*y + z;
> > double r2 = fma(x, y, z);
> > n += r1 != r2;
> > }
> > printf("%d\n", n);
> > return 0;
> >}
> >
> >It is certainly worth a bug report, but I am afraid that Microsoft
> >will do nothing to fix it, likely claiming that they don't care
> >about old hardware.
>
> Just FYI - it also returns 0 when compiled by Clang on an ARM Mac.
>
Looks like a bug in clang.
New versions of clang generate FMA instead of mul+add. I.e. clang bug is
opposite of MS bug.
By Standard, compilers not allowed to do it in "standard" C mode in
absence of special flags like -ffast-math.
I played a little on godbolt and it seems that the bug is relatively
new. clang 13 still generates correct code. clang 14 does not. I.e.
slightly less than 3 years.
It happened simultaneously on x86-64 and ARM64
clang 14
https://godbolt.org/z/asochKz5P
https://godbolt.org/z/c7xTaGWzv
clang 13
https://godbolt.org/z/6onP3dE3c
https://godbolt.org/z/W9exqTanf
clang 13 -ffast-math
https://godbolt.org/z/8f875qMrf
https://godbolt.org/z/qPGafr563
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a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 11:48 +0100
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 12:00 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 13:48 +0100
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 13:09 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 14:22 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:13 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 16:19 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:52 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 09:09 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:17 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-25 17:26 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:45 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:57 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-25 19:17 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 18:58 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 00:36 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-26 04:15 +0100
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-26 08:16 +0000
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 14:27 +0200
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-26 14:39 +0000
FP_CONTRACT was : a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-28 16:28 +0200
Re: FP_CONTRACT was : a MSVC and glibc-compatible fmod() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-01 08:35 -0800
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 16:22 +0200
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 15:10 +0000
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:33 +0200
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 16:48 +0000
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-24 22:21 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 07:37 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-25 23:03 +0000
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 02:00 +0200
Re: a MSVC and glibc-compatible fmod() Wuns Haerst <Wuns.Haerst@wurstfabrik.at> - 2025-02-26 04:01 +0100
Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-25 08:24 +0000
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-27 21:16 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 07:59 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-28 12:35 +0200
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 18:12 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 19:23 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 18:30 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 19:31 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 19:47 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 20:49 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 14:37 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 16:58 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 17:11 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 21:02 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 20:32 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 21:37 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 20:45 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 09:40 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-01 22:55 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 18:54 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:59 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 15:41 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:10 +0100
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-02 16:22 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:26 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:07 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:09 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:11 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:52 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:55 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 20:09 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:14 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:57 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 22:58 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 12:52 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 18:10 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 23:55 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-07 09:51 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 18:20 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 17:30 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 19:27 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 18:39 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 02:01 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:37 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:41 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 20:00 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:01 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 01:31 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 07:41 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 11:08 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 10:31 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 11:46 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 10:54 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 12:09 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 11:21 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:09 +0200
Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-09 15:26 +0000
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 17:02 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 19:55 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:10 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:27 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 17:23 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 20:04 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:11 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 20:11 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 07:24 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 10:46 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 14:26 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 13:45 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 16:33 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 15:46 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 16:59 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 16:11 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 17:43 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 17:13 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 19:51 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 19:00 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 20:38 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 22:34 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 22:36 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 12:47 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 23:52 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 23:57 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 09:34 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 12:29 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 12:12 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 13:34 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 13:10 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 14:55 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 14:08 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 15:46 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 13:51 +0200
Re: a MSVC and glibc-compatible fmod() James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-03-11 14:21 -0400
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 20:28 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-16 13:48 +0200
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 13:17 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 12:53 +0100
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 12:54 +0100
Re: a MSVC and glibc-compatible fmod() wij <wyniijj5@gmail.com> - 2025-03-09 18:51 +0800
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 12:56 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:23 +0200
Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 13:39 +0100
Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:56 +0200
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