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

[Bruce Evans]

bde         2005-11-23 02:06:07 UTC

  FreeBSD src repository

  Modified files:
    lib/msun/src         e_rem_pio2f.c 
  Log:
  Quick fix for stack buffer overrun in rev.1.13.  Oops.  The prec == 1
  arg to __kernel_rem_pio2() gives 53-bit (double) precision, not single
  precision and/or the array dimension like I thought.  prec == 2 is
  used in e_rem_pio2.c for double precision although it is documented
  to be for 64-bit (extended) precision, and I just reduced it by 1
  thinking that this would give the value suitable for 24-bit (float)
  precision.  Reducing it 1 more to the documented value for float
  precision doesn't actually work (it gives errors of ~0.75 ulps in the
  reduced arg, but errors of much less than 0.5 ulps are needed; the bug
  seems to be in kernel_rem_pio2.c).  Keep using a value 1 larger than
  the documented value but supply an array large enough hold the extra
  unused result from this.
  
  The bug can also be fixed quickly by increasing init_jk[0] in
  k_rem_pio2.c from 2 to 3.  This gives behaviour identical to using
  prec == 1 except it doesn't create the extra result.  It isn't clear
  how the precision bug affects higher precisions.  113-bit (quad) is
  the largest precision, so there is no way to use a large precision
  to fix it.
  
  Revision  Changes    Path
  1.18      +4 -4      src/lib/msun/src/e_rem_pio2f.c