From: Paul Zimmermann <Paul.Zimmermann@inria.fr>
To: Jeff Johnston <jjohnstn@redhat.com>
Cc: newlib@sourceware.org, joel@rtems.org
Subject: Re: incorrectly rounded square root
Date: Wed, 02 Jun 2021 09:51:17 +0200 [thread overview]
Message-ID: <mwfsy0d7re.fsf@tomate.loria.fr> (raw)
In-Reply-To: <CAOox84v54CvMzcmBY_Ax1aYV4rZDE7VQRKsug5-5qAcaFU+H0Q@mail.gmail.com> (message from Jeff Johnston on Tue, 1 Jun 2021 12:28:41 -0400)
Hi Jeff,
thank you for your answer. After investigating more it seems fesetround()
is ineffective with newlib. Indeed if I print the result of fegetround()
just after the fesetround() calls I get:
fegetround: 0
RNDN: 0x1.ff83fp+63
fegetround: 0
RNDZ: 0x1.ff83fp+63
fegetround: 0
RNDU: 0x1.ff83fp+63
fegetround: 0
RNDD: 0x1.ff83fp+63
whereas with GNU libc I get:
fegetround: 0
RNDN: 0x1.ff83fp+63
fegetround: 3072
RNDZ: 0x1.ff83eep+63
fegetround: 2048
RNDU: 0x1.ff83fp+63
fegetround: 1024
RNDD: 0x1.ff83eep+63
Thus it seems this has nothing to do with the square root.
According to gdb the fesetround() code used is the following:
(gdb) break fesetround
Breakpoint 1 at 0x1650: file ../../../../../../newlib/libm/machine/x86_64/fenv.c, line 371.
Paul
next prev parent reply other threads:[~2021-06-02 7:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-04 8:08 Paul Zimmermann
2021-05-31 20:52 ` Jeff Johnston
2021-06-01 7:11 ` Paul Zimmermann
2021-06-01 16:28 ` Jeff Johnston
2021-06-02 7:51 ` Paul Zimmermann [this message]
2021-06-02 13:07 ` Joel Sherrill
2021-06-02 18:43 ` Jeff Johnston
2021-06-02 19:07 ` Marco Atzeri
2021-06-02 19:12 ` Joel Sherrill
2021-06-03 3:01 ` Jeff Johnston
2021-06-03 10:21 ` Paul Zimmermann
2021-06-03 15:50 ` Jeff Johnston
2021-06-04 7:14 ` Paul Zimmermann
2021-06-04 18:44 ` Jeff Johnston
2021-06-04 18:59 ` Joel Sherrill
2021-06-05 13:25 ` Brian Inglis
2021-06-07 9:51 ` Paul Zimmermann
2021-06-12 22:31 ` Maciej W. Rozycki
2021-06-03 11:25 ` Paul Zimmermann
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