cvs commit: src/lib/msun/src e_rem_pio2f.c

[Bruce Evans]

bde         2005-10-29 08:15:30 UTC

  FreeBSD src repository

  Modified files:
    lib/msun/src         e_rem_pio2f.c 
  Log:
  Start trying to make the float precision trig functions actually worth
  using under FreeBSD.  Before this commit, all float precision functions
  except exp2f() were implemented using only float precision, apparently
  because Cygnus needed this in 1993 for embedded systems with slow or
  inefficient double precision.  For FreeBSD, except possibly on systems
  that do floating point entirely in software (very old i386 and now
  arm), this just gives a more complicated implementation, many bugs,
  and usually worse performance for float precision than for double
  precision.  The bugs and worse performance were particulary large in
  arg reduction for trig functions.  We want to divide by an approximation
  to pi/2 which has as many as 1584 bits, so we should use the widest
  type that is efficient and/or easy to use, i.e., double.  Use fdlibm's
  __kernel_rem_pio2() to do this as Sun apparently intended.  Cygnus's
  k_rem_pio2f.c is now unused.  e_rem_pio2f.c still needs to be separate
  from e_rem_pio2.c so that it can be optimized for float args.  Similarly
  for long double precision.
  
  This speeds up cosf(x) on large args by a factor of about 2.  Correct
  arg reduction on large args is still inherently very slow, so hopefully
  these args rarely occur in practice.  There is much more efficiency
  to be gained by using double precision to speed up arg reduction on
  medium and small float args.
  
  Revision  Changes    Path
  1.13      +28 -30    src/lib/msun/src/e_rem_pio2f.c