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From: "liubov.dmitrieva at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sources.redhat.com
Subject: [Bug math/14470] New: Inaccurate j1f function on x86_32
Date: Wed, 15 Aug 2012 14:10:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=14470

             Bug #: 14470
           Summary: Inaccurate j1f function on x86_32
           Product: glibc
           Version: 2.17
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: liubov.dmitrieva@gmail.com
    Classification: Unclassified


Test case:

// gcc main.c -std=c99 -lm -m32

#include <stdio.h>
#include <fenv.h>
#include <stdlib.h>  // abs function for int argument

extern float j1f(float);
extern double j1(double);

#define i32(a)    (((int*)&(a))[0])

int main() {
    float a,r1,r2;

    i32(a)=0x4122c68a;    //argument

    fesetround(FE_TONEAREST);

    r1 = j1f(a);  //actual result
    r2 = j1(a);   //actual result 2

    printf("inputs: a = (0x%08x)\t%e\n", i32(a), a);
    printf("actual    = (0x%08x)\t%.13e\n", i32(r1), r1);
    printf("expected  = (0x%08x)\t%.13e\n", i32(r2), r2);
    printf("error     = %d ulp\n", abs(i32(r1) - i32(r2)));

    return 0;
}

Results:

inputs: a = (0x4122c68a)        1.017347e+01
actual    = (0xb55e2ad3)        -8.2763762065952e-07
expected  = (0xb55e40c6)        -8.2795702383009e-07
error     = 5619 ulp

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