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From: "florian at schanda dot org.uk" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug math/26045] New: fmaxf(inf, nan) does not always work Date: Tue, 26 May 2020 12:43:10 +0000 [thread overview] Message-ID: <bug-26045-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=26045 Bug ID: 26045 Summary: fmaxf(inf, nan) does not always work Product: glibc Version: 2.28 Status: UNCONFIRMED Severity: normal Priority: P2 Component: math Assignee: unassigned at sourceware dot org Reporter: florian at schanda dot org.uk Target Milestone: --- Created attachment 12570 --> https://sourceware.org/bugzilla/attachment.cgi?id=12570&action=edit example showing fmaxf does not always work Hi The gcc people sent me here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95329 I believe the fmaxf function does not always work correctly (I am on Debian stable, amd64). The following piece of code produces the wrong output when compile with no optimisation (and hence fmaxf from libm is called): $ gcc bug.c -lm $ ./a.out max(-inf, nan) = nan max(-inf, nan) = -inf The code in question uses a special hand-crafted NaN: #include <stdio.h> #include <stdint.h> #include <math.h> #include <string.h> int main() { uint32_t bv = 0x7FACBA7E; // (0 11111111 01011001011101001111110) float a, b; a = -INFINITY; memcpy(&b, &bv, 4); printf("max(%f, %f) = %f\n", a, b, fmaxf(a, b)); b = NAN; printf("max(%f, %f) = %f\n", a, b, fmaxf(a, b)); } Thanks in advance, and good luck! :) -- You are receiving this mail because: You are on the CC list for the bug.
next reply other threads:[~2020-05-26 12:43 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-26 12:43 florian at schanda dot org.uk [this message] 2020-05-27 9:59 ` [Bug math/26045] " amonakov at gmail dot com 2020-06-01 22:52 ` joseph at codesourcery dot com 2020-06-02 6:18 ` amonakov at gmail dot com 2020-06-02 13:59 ` joseph at codesourcery dot com 2021-09-29 16:19 ` jsm28 at gcc dot gnu.org
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