Re: [cc65] possible error, tertiary on cbm_save return value

On Sun, Aug 23, 2009 at 08:27:25PM +0200, Johan Kotlinski wrote:
> It seems wrong to me, that it checks the return from cbm_save using x.
> Isn't the return value in a?

One of the basic rules of expression evaluation in C is, that all characters
are promoted to ints. This means that the above is correct code. So with 8-bit
chars

        unsigned char C = 0x01;
        unsigned char S = 8;
        int I = C << S;

gives 0x100, and not some undefined value (as it would be if the shift
operation would act on characters).

Another rule says that the compiler may do what it wants as long as the
compiled code behaves as if all rules of the standard have been followed. This
rule is called the "as if" rule. This means that the compiler is free to
operate on characters (or whatever) as long this does not change the result.
In the given case, the compiler could just check the A register, but it's not
required to.

Please note that this does also mean that assembler routines that return
characters must actually return an integer value!

Regards


        Uz


-- 
Ullrich von Bassewitz                                  uz@musoftware.de
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