🚀 go-pugleaf

I wrote:

> > Thus even in ANSI C, if this function is called this way:
> >
> >	extern short p, q, r, test(short,short);
> >	r = test(p,q);
> >
> > the values from p and q are still converted from short to int and back
> > to short.  

Thad Smith (ThadSmith@acm.org) responded:
> I find nothing in the Standard that states that the arguments undergo
> integral promotions before being assigned to the function parameters.

This is in 6.2.1.1/3.2.1.1, the passage which defines the integral
promotions.  It states that the promotions apply

#  in an expression wherever an int or unsigned int may be used.

Since the call test(1,2) is permissible, this means that p and q must
be promoted to int.  As noted in my previous posting, they are then
converted right back to short within the caller (since a prototype
was used), and the compiler can easily optimize this out.

Another example of this sort of thing is an assignment expression like
p=q, where p and q are short.  q is promoted to int, then demoted back
to short; since the value cannot change, the compiler optimizes out the
conversions.  If you write p=(short)q, then the same reason applies
to each of the expressions q and (short)q, and you end up with *two*
round-trip conversions which should be optimized out.
-- 
Mark Brader, msb@sq.com         "Mark is probably right about something,
SoftQuad Inc., Toronto           but I forget what"     -- Rayan Zachariassen

My text in this article is in the public domain.