On Mon, Apr 20, 2015 at 12:03:11PM +0100, Kyrill Tkachov wrote:
> The definition and comment on IN_RANGE in system.h is:
> /* A macro to determine whether a VALUE lies inclusively within a
> certain range without evaluating the VALUE more than once. This
> macro won't warn if the VALUE is unsigned and the LOWER bound is
> zero, as it would e.g. with "VALUE >= 0 && ...". Note the LOWER
> bound *is* evaluated twice, and LOWER must not be greater than
> UPPER. However the bounds themselves can be either positive or
> negative. */
> #define IN_RANGE(VALUE, LOWER, UPPER) \
> ((unsigned HOST_WIDE_INT) (VALUE) - (unsigned HOST_WIDE_INT) (LOWER) \
> <= (unsigned HOST_WIDE_INT) (UPPER) - (unsigned HOST_WIDE_INT) (LOWER))
>
> Since it works on positive or negative bounds, I'd think it would work on
> signed numbers, wouldn't it?
Of course it does, as long as the types of VALUE, LOWER and UPPER aren't
wider integer types than {,un}signed HOST_WIDE_INT. As HWI is always 64-bit
now, that just means it wouldn't work for 128-bit integral types that aren't
used anywhere in GCC. So, just don't use IN_RANGE for floating point
values, that might have surprising effects, otherwise it is safe to use it.
Jakub
