[cfe-dev] [RFC] Introduce overflow builtins

[Joerg Sonnenberger]

On Mon, Mar 19, 2012 at 02:03:34AM -0400, Xi Wang wrote:
> With overflow builtins, programmers can implement the example
> as follows.
> 
> void *malloc_array(size_t n, size_t size)
> {
> 	size_t bytes;
> 	if (__overflow_umul(&bytes, n, size))
> 		return NULL;
> 	return malloc(bytes);
> }

I see two different options for the functions:

(1) Provide __overflow_ # op which derives the types from the arguments.
In that case it should be just add, sub, div, mul, rem.

(2) Provide __overflow_ # op # _ # type which is explicitly typed. Op is
still naturally add, sub, div, mul, rem.

Using "umul" doesn't add any value IMO. One practical issue is how
should div/rem work for 0?

Joerg