cvs commit: parrot/src dod.c

[Nicholas Clark]

cvsuser     04/10/26 08:01:29

  Modified:    src      dod.c
  Log:
  a << 8 * sizeof(a) is undefined behaviour in C. (ie the answer isn't always 0)
  So need to take care of this case explicitly.
  
  Revision  Changes    Path
  1.138     +9 -2      parrot/src/dod.c
  
  Index: dod.c
  ===================================================================
  RCS file: /cvs/public/parrot/src/dod.c,v
  retrieving revision 1.137
  retrieving revision 1.138
  diff -u -r1.137 -r1.138
  --- dod.c     22 Oct 2004 13:29:36 -0000      1.137
  +++ dod.c     26 Oct 2004 15:01:29 -0000      1.138
  @@ -1,6 +1,6 @@
   /*
   Copyright: 2001-2003 The Perl Foundation.  All Rights Reserved.
  -$Id: dod.c,v 1.137 2004/10/22 13:29:36 leo Exp $
  +$Id: dod.c,v 1.138 2004/10/26 15:01:29 nicholas Exp $
   
   =head1 NAME
   
  @@ -924,13 +924,20 @@
       int i;
       int bound = sizeof(size_t) * 8;
   
  -    for (i = 0; i <= bound; i++) {
  +    /* Shifting a value by its size (in bits) or larger is undefined behaviour.
  +       so need an explict check to return 0 if there is no prefix, rather than
  +       attempting to rely on (say) 0xFFFFFFFF << 32 being 0  */
  +    for (i = 0; i < bound; i++) {
           if (val1 == val2) {
               return ~(size_t)0 << i;
           }
           val1 >>= 1;
           val2 >>= 1;
       }
  +    if (val1 == val2) {
  +        assert(i == bound);
  +        return 0;
  +    }
   
       internal_exception(INTERP_ERROR,
               "Unexpected condition in find_common_mask()!\n");