[Bug 713985] Re: [armel] Function tgammal has precision issues in version 2.12.1-0ubuntu10.2 on ARM

Dima Pasechnik 713985 at bugs.launchpad.net
Mon Jan 9 04:15:37 UTC 2012


The bug is in fact in lgammal, as tgammal(x) simply takes expl(lgammal(x)); 
namely, lgammal(6.0) produces 4.78749174278204581157 on armel, 
while it should be   closer to      4.7874917427820459942477, i.e. armel gives relative error of about 3.8e-17

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Title:
  [armel] Function tgammal has precision issues in version
  2.12.1-0ubuntu10.2 on ARM

Status in “eglibc” package in Ubuntu:
  New

Bug description:
  Consider the following test program :
  #include <stdio.h>
  #include <math.h>
   
  int
  main (int argc,
        char* argv[])
  {
    long double x = 6.0;
    printf("tgammal (%.20Lf)=%.20Lfn", x, tgammal(x));
    return 0;
  }

  When run on 2.12.1-0ubuntu10.2, the result is :
  tgammal (6.00000000000000000000)=119.99999999999997157829
  while when run on 2.11.2-11 (glibc's unstable), the result is :
  tgammal (6.00000000000000000000)=119.99999999999999998612

  The second result is acceptable, while the second isn't. This makes
  sage (http://www.sagemath.org) unhappy...

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