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

[David Schultz]

das         2004-06-09 21:24:52 UTC

  FreeBSD src repository

  Modified files:
    lib/msun/src         s_rintf.c 
  Log:
  Fix a bug where rintf() rounded the wrong way in round-to-nearest mode
  on all inputs of the form x.75, where x is an even integer and
  log2(x) = 21.  A similar problem occurred when rounding upward.
  The bug involves the following snippet copied from rint():
  
          i>>=1;
          if((i0&i)!=0) i0 = (i0&(~i))|((0x100000)>>j0);
  
  The constant 0x100000 should be 0x200000.  Apparently this case was
  never tested.
  
  It turns out that the bit manipulation is completely superfluous
  anyway, so remove it.  (It tries to simulate 90% of the rounding
  process that the FPU does anyway.)  Also, the special case of +-0 is
  handled twice (in different ways), so remove the second instance.
  
  Throw in some related simplifications from bde:
  
  - Work around a bug where gcc fails to clip to float precision by
    declaring two float variables as volatile.  Previously, we
    tricked gcc into generating correct code by declaring some
    float constants as doubles.
  
  - Remove additional superfluous bit manipulation.
  
  - Minor reorganization.
  
  - Include <sys/types.h> explicitly.
  
  Note that some of the equivalent lines in rint() also appear to be
  unnecessary, but I'll defer to the numerical analysts who wrote it,
  since I can't test all 2^64 cases.
  
  Discussed with: bde
  
  Revision  Changes    Path
  1.9       +7 -26     src/lib/msun/src/s_rintf.c