Re: pointer arithmetics and casts

[Neil Booth <neil@daikokuya.co.uk>]

Al Viro wrote:-

> But that means a fsckload of extra nodes allocated on pretty much any
> program - use of arrays is not rare and indices tend to be int, so we
> hit an extra allocated node on each such place.
> 
> Another possible solution is to add a primitive for combined conversion
> and multiplication - basically, convert the first argument to the type of
> the second one and multiply.  We would actually need it only for ptrdiff_t;
> sizeof(*p) is going to fit into the range anyway (it has to - the difference
> between (char *)(p+1) and (char *)p must fit into it, or we couldn't do any
> arithmetics on that pointer type at all; as soon as product overflows
> ptrdiff_t we are free to do whatever the hell we like, since that's an
> undefined behaviour and "multiply as ptrdiff_t values" gives an reasonable
> result even in such cases).

Perhaps not overloading the "+" node; reserve that for arithmetic types.
Have a ptr_add, (maybe) ptr_sub, and ptr_diff operations.

GCC's moved to having at least a ptr_add recently.

Neil.