[Cryptography] GCC bug 30475 (was Re: bounded pointers in C)

[Viktor Dukhovni]

On Fri, Apr 25, 2014 at 07:05:15AM -0400, Jerry Leichter wrote:

> It's easy to determine the maximum value of an *unsigned* type.
> It's not clear to me now that there is any portable way to determine
> the maximum value of a *signed* type.

Indeed, nothing obvious comes to mind.  My work-around requires
C99 intmax_t.  I do all arithmetic for off_t using safe intmax_t
arithmetic instead (which comes with INTMAX_MAX), and then at the
end make sure that casting to off_t does not truncate the value:

    off_t mumble(off_t input, ...)
    {
	intmax_t tmp = input;
	off_t result;

	/* safe intmax_t arithmetic using tmp */

	result = (off_t) tmp;
	if (result != tmp)
	    /* error */

	return result;
    }

This is a pain.  And as I mentioned, I'd like to avoid a C99
dependency, but don't see any portable way to do that.

-- 
	Viktor.