Re: [PATCH] Remove pointless <0 comparison for unsigned variable in fs/fcntl.c

Jesper Juhl
2004-11-23T23:04:30Z

On Tue, 23 Nov 2004, Timur Tabi wrote:

> Linus Torvalds wrote:
>
> > which might warn on an architecture where "pid_t" is just sixteen bits wide.
> > Does that make the code wrong? Hell no.
>
> Wouldn't something like "sizeof(pid_t) > 2" be a better test? It certainly
> would be a lot easier to understand than comparing with 0xffff.
>
That was not the point of the example Linus gave.
The example Linus gave was a function taking a pid_t argument and then
comparing the value of the argument passed against 0xffff - the /value/ of
the pid_t argument passed, not the size of the datatype.

int fn(pid_t a)
{
if (a > 0xffff)
...
}

if pid_t is 16 bit, then the value can never be greater than 0xffff but,
if pid_t is greater than 16 bit, say 32 bit, then the argument "a" could
very well contain a value greater than 0xffff and then the comparison
makes perfect sense. So, while you'd get a warning on architectures where
pid_t is 16bit or less you won't get a warning when pid_t is greater than
16 bit. "fixing" that warning would clearly be wrong, no argument about
that.

--
Jesper Juhl