cvs commit: src/lib/msun/src e_log.c e_logf.c

[Bruce Evans]

bde         2006-07-07 04:33:08 UTC

  FreeBSD src repository

  Modified files:
    lib/msun/src         e_log.c e_logf.c 
  Log:
  Fixed the threshold for using the simple Taylor approximation.
  
  In e_log.c, there was just a off-by-1 (1 ulp) error in the comment
  about the threshold.  The precision of the threshold is unimportant,
  but the magic numbers in the code are easier to understand when the
  threshold is described precisely.
  
  In e_logf.c, mistranslation of the magic numbers gave an off-by-1
  (1 * 16 ulps) error in the intended negative bound for the threshold
  and an off-by-7 (7 * 16 ulps) error in the intended positive bound for
  the threshold, and the intended bounds were not translated from the
  double precision bounds so they were unnecessarily small by a factor
  of about 2048.
  
  The optimization of using the simple Taylor approximation for args
  near a power of 2 is dubious since it only applies to a relatively
  small proportion of args, but if it is done then doing it 2048 times
  as often _may_ be more efficient.  (My benchmarks show unexplained
  dependencies on the data that increase with further optimizations
  in this area.)
  
  Revision  Changes    Path
  1.11      +1 -1      src/lib/msun/src/e_log.c
  1.9       +1 -1      src/lib/msun/src/e_logf.c