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From: "zimmerma+gcc at loria dot fr" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/26982] New: [x86_64] x86_64 lgamma has too large ULP error
Date: Mon, 30 Nov 2020 10:27:23 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26982

            Bug ID: 26982
           Summary: [x86_64] x86_64 lgamma has too large ULP error
           Product: glibc
           Version: 2.32
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: zimmerma+gcc at loria dot fr
                CC: joseph at codesourcery dot com
  Target Milestone: ---

$ cat test.c
#include <stdio.h>
#include <math.h>

int main()
{
  double x =3D -0x1.f60c969a239f2p+1, y;
  y =3D lgamma (x);
  printf ("x=3D%a y=3D%a\n", x, y);
}
$ gcc -fno-builtin test.c -lm
$ ./a.out
x=3D-0x1.f60c969a239f2p+1 y=3D-0x1.fd3d359162ae4p-2

The correctly rounded result is -0x1.fd3d359162adap-2, thus the error is 10
ulps, which is larger than the maximum accepted limit of 9 ulps.

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