Re: Aliasing problems in GNU Chill?

[Jeffrey A Law <law@cygnus.com>]

  In message <19990902102549.A3136@x8b4e53cd.dhcp.okstate.edu>you write:
  > On Thu, Sep 02, 1999 at 12:43:26AM -0600, Jeffrey A Law wrote:
  > >   In message <19990901144104.A6143@x8b4e53cd.dhcp.okstate.edu>you write:
  > >   > I was reading through andps.c in libchill recently and came across th
  > is.
  > >   > 
  > >   >   else if (bitlength <= SET_SHORT_SIZE)
  > >   >     {
  > >   >       *((SET_SHORT *)out) = *((SET_SHORT *)left) &
  > >   >                             *((SET_SHORT *)right);
  > >   >       MASK_UNUSED_SHORT_BITS((SET_SHORT *)out, bitlength);
  > >   >     }
  > >   > 
  > >   > It appears to me that this suffers from the same aliasing problems th
  > at
  > >   > we've  been hearing about recently. No?
  > > Yes.
  > No. SET_SHORT & friends are unsigned char when USE_CHARS is set, and
  > it's unconditionally set. Hence the exception for char* pointers comes
  > into play (I believe.) 
Ah.  OK.  I'll update powerset.h to prevent people from disabling USE_CHARS :-)

jeff




  > 
  > It could use some changes (the above block is dead code with USE_CHARS defi
  > ned),
  > but it appears to be correct.
  > 
  >