This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: 1 << BITS_PER_UNIT
- To: Alexandre Oliva <oliva at dcc dot unicamp dot br>
- Subject: Re: 1 << BITS_PER_UNIT
- From: Richard Earnshaw <rearnsha at arm dot com>
- Date: Mon, 26 Oct 1998 09:44:51 +0000
- Cc: Michael Hayes <m dot hayes at elec dot canterbury dot ac dot nz>, egcs at cygnus dot com
- Cc: richard dot earnshaw at arm dot com
- Organization: ARM Ltd.
- Reply-To: richard dot earnshaw at arm dot com
> Did you run:
>
> #include <stdio.h>
> #define BITS_PER_UNIT 8
> main() {
> printf("%x %x\n",
> (1 << BITS_PER_UNIT) - 1,
> (2 << (BITS_PER_UNIT - 1)));
> }
I wasn't suggesting ((1 << x) - 1) == (2 << (x - 1)), that is obviously
false, but (1 << x) == (2 << (x - 1)). Do some elementary math.
The point is that (1 << BITS_PER_UNIT) - 1 gets you a warning, but
(2 << (BITS_PER_UNIT - 1)) - 1 gives the same result but no warning, and
is well within the spec since (BITS_PER_UNIT - 1) is less than the word
size.
Richard.