On Tue, 27 Aug 2013, Richard Sandiford wrote:
> Kenneth Zadeck <zad...@naturalbridge.com> writes:
> > fixed fits_uhwi_p.
> >
> > tested on x86-64.
> >
> > kenny
> >
> > Index: gcc/wide-int.h
> > ===================================================================
> > --- gcc/wide-int.h (revision 201985)
> > +++ gcc/wide-int.h (working copy)
> > @@ -1650,7 +1650,7 @@ wide_int_ro::fits_shwi_p () const
> > inline bool
> > wide_int_ro::fits_uhwi_p () const
> > {
> > - return len == 1 || (len == 2 && val[1] == 0);
> > + return (len == 1 && val[0] >= 0) || (len == 2 && val[1] == 0);
> > }
>
> With upper bits being undefined, it doesn't seem safe to check
Err - we're back at upper bits being undefined? Ugh. Then
having both fits_uhwi_p and fits_shwi_p doesn't make sense.
> val[0] or val[1] like this. I was thinking along the lines of:
>
> inline bool
> wide_int_ro::fits_uhwi_p () const
> {
> if (precision <= HOST_BITS_PER_WIDE_INT)
> return true;
> if (len == 1)
> return val[0] >= 0;
> if (precision < HOST_BITS_PER_WIDE_INT * 2)
> return ((unsigned HOST_WIDE_INT) val[1]
> << (HOST_BITS_PER_WIDE_INT * 2 - precision)) == 0;
> return val[1] == 0;
> }
>
> Since we don't have a sign, everything HWI-sized or smaller fits in a
> uhwi without loss of precision.
Which then means fits_hwi_p () is simply
if (precision <= HOST_BITS_PER_WIDE_INT)
return true;
zext (); // ick, modification in a predicate! stupid undefined bits!
return len == 1 || (len == 2 && val[1] == 0);
but if upper bits are undefined then the whole encoding and len
business is broken.
Richard.
