Re: /internet

[Joe Buck <jbuck@Synopsys.COM>]

> > Does IEEE require left-to-right evaluation of y = a * b * c * d;
> > when there are no parentheses present?
> 
> I think that IEEE does not actually say anything about it.  C9X, however,
> does contain some remarks such as the following, which might have come
> from NCEG.

>                int a, b;
>                /* ... */
>                a = a + 32760 + b + 5;
> 
>        the expression statement behaves exactly the same as
> 
>                a = (((a + 32760) + b) + 5);
>
>        due to the associativity and precedence of these  operators.
>        Thus,  the result of the sum (a + 32760) is next added to b,
>        and that result is then added to  5  which  results  in  the
>        value  assigned  to  a.   On  a  machine  in which overflows
>        produce an explicit trap and in which the  range  of  values
>        representable   by   an   int   is   [-32768,  +32767],  the
>        implementation cannot rewrite this expression as
> 
>                a = ((a + b) + 32765);

Amazing.  These guys are trying to turn C into Ada.

If this is the rule, then a*b*c*d can't be rearranged in C9X.  However,
it appears that it can be rearranged in Fortran (where the user must
use parentheses to force the order of evaluation) as well as in the
current ANSI/ISO C.