From: Szabolcs Nagy <nsz@port70.net>
To: Paul Zimmermann <Paul.Zimmermann@inria.fr>, musl@lists.openwall.com
Subject: Re: [musl] issue with sinhf
Date: Fri, 5 Feb 2021 21:12:29 +0100 [thread overview]
Message-ID: <20210205201229.GD2447252@port70.net> (raw)
In-Reply-To: <20210205200934.GC2447252@port70.net>
[-- Attachment #1: Type: text/plain, Size: 704 bytes --]
* Szabolcs Nagy <nsz@port70.net> [2021-02-05 21:09:34 +0100]:
> * Paul Zimmermann <Paul.Zimmermann@inria.fr> [2021-02-05 09:01:09 +0100]:
> > $ cat test_sinh_musl.c
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <math.h>
> >
> > int
> > main ()
> > {
> > float x = 0x1.62e4p+6;
> > float y = sinhf (x);
> > printf ("x=%a y=%a\n", x, y);
> > }
> ...
> > $ gcc -fno-builtin test_sinh_musl.c $FILES
> > $ ./a.out
> > x=0x1.62e4p+6 y=-nan
>
> this seems to be a bug, attaching a fix
that one was for the acoshf bug, the sinhf issue was a bug
in expm1f (overflowed too early, although sinhf could have
used a less tight threshold that would have prevented this
causing an issue there)
[-- Attachment #2: 0001-math-fix-expm1f-overflow-threshold.patch --]
[-- Type: text/x-diff, Size: 1126 bytes --]
From 09f8837310082aeee019828b9aa805cf4528b3d1 Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <nsz@port70.net>
Date: Fri, 5 Feb 2021 19:51:36 +0000
Subject: [PATCH] math: fix expm1f overflow threshold
the threshold was wrong so expm1f overflowed to inf a bit too early
and on most targets uint32_t compare is faster than float compare so
use that.
this also fixes sinhf incorrectly returning nan for some values where
the internal expm1f overflowed.
---
src/math/expm1f.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/src/math/expm1f.c b/src/math/expm1f.c
index 297e0b44..09a41afe 100644
--- a/src/math/expm1f.c
+++ b/src/math/expm1f.c
@@ -16,7 +16,6 @@
#include "libm.h"
static const float
-o_threshold = 8.8721679688e+01, /* 0x42b17180 */
ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
invln2 = 1.4426950216e+00, /* 0x3fb8aa3b */
@@ -41,7 +40,7 @@ float expm1f(float x)
return x;
if (sign)
return -1;
- if (x > o_threshold) {
+ if (hx > 0x42b17217) { /* x > log(FLT_MAX) */
x *= 0x1p127f;
return x;
}
--
2.29.2
next prev parent reply other threads:[~2021-02-05 20:12 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-05 8:01 Paul Zimmermann
2021-02-05 20:09 ` Szabolcs Nagy
2021-02-05 20:12 ` Szabolcs Nagy [this message]
2021-02-06 6:34 ` Paul Zimmermann
2021-02-06 6:29 ` Paul Zimmermann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210205201229.GD2447252@port70.net \
--to=nsz@port70.net \
--cc=Paul.Zimmermann@inria.fr \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).