Re: ptrdiff_t misuse [was :Re: (empty)]

[Paul Eggert <eggert@cs.ucla.edu>]

On 07/05/2012 12:34 PM, Eli Zaretskii wrote:
>     ptrdiff_t hscroll_max = min (MOST_POSITIVE_FIXNUM, PTRDIFF_MAX);
>     ptrdiff_t new_hscroll = clip_to_bounds (0, hscroll, hscroll_max);
> 
> Won't this do The Wrong Thing when Emacs is configured with wide ints?

No, because hscroll_max and new_hscroll cannot
exceed PTRDIFF_MAX (the above code guarantees
this directly), so their values therefore always fit
in ptrdiff_t range even when EMACS_INT is wider than
ptrdiff_t.

Similarly, buffer and string positions cannot exceed
BUF_BYTES_MAX and STRING_BYTES_MAX, which in turn
cannot exceed PTRDIFF_MAX; so ptrdiff_t always
suffices for them too.

If we change hscroll values from ptrdiff_t to int, as
I think Dmitry is proposing, the above code should be
changed to use int and INT_MAX instead of ptrdiff_t
and PTRDIFF_MAX.