public inbox for glibc-bugs@sourceware.org help / color / mirror / Atom feed
From: "wxzkenny at aliyun dot com" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug libc/31227] New: The value of cos varies with different optimization levels Date: Wed, 10 Jan 2024 01:20:49 +0000 [thread overview] Message-ID: <bug-31227-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=31227 Bug ID: 31227 Summary: The value of cos varies with different optimization levels Product: glibc Version: 2.28 Status: UNCONFIRMED Severity: normal Priority: P2 Component: libc Assignee: unassigned at sourceware dot org Reporter: wxzkenny at aliyun dot com CC: drepper.fsp at gmail dot com Target Milestone: --- I wrote a test case test_cos.c, the context of file test_cos.c as following: #include <stdio.h> #include <math.h> static double dcos(double arg1) { return cos(arg1); } int main() { double d = 17.14159265; volatile double c = dcos(d); printf("cos(d) = %.17f %llx\n", c, *(long long*)&c); return 0; } When we compiled with different optimization levels, we got different results: [root@localhost tmp]# gcc -o test_cos -lm -O test_cos.c && ./test_cos cos(d) = -0.13673722176390943 bfc1809af3cf9a1b [root@localhost tmp]# gcc -o test_cos -lm -O0 test_cos.c && ./test_cos cos(d) = -0.13673722176390940 bfc1809af3cf9a1a [root@localhost tmp]# gcc -o test_cos -lm -O1 test_cos.c && ./test_cos cos(d) = -0.13673722176390943 bfc1809af3cf9a1b [root@localhost tmp]# gcc -o test_cos -lm -O2 test_cos.c && ./test_cos cos(d) = -0.13673722176390943 bfc1809af3cf9a1b [root@localhost tmp]# gcc -o test_cos -lm -O3 test_cos.c && ./test_cos cos(d) = -0.13673722176390943 bfc1809af3cf9a1b When I embed cos in my large program and compile it with -O2 I get the same result as here with -O0 -- You are receiving this mail because: You are on the CC list for the bug.
next reply other threads:[~2024-01-10 1:20 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-01-10 1:20 wxzkenny at aliyun dot com [this message] 2024-01-10 9:38 ` [Bug libc/31227] " schwab@linux-m68k.org 2024-01-11 3:20 ` wxzkenny at aliyun dot com
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=bug-31227-131@http.sourceware.org/bugzilla/ \ --to=sourceware-bugzilla@sourceware.org \ --cc=glibc-bugs@sourceware.org \ /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: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
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 read-only IMAP folder(s) and NNTP newsgroup(s).