Re: [avr-gcc-list] mass stupidity with registers and longs

[Russell Shaw]

Curtis Maloney wrote:
> I give up.  I've been trying to shift 4 chars into an unsigned long, but 
> can't stop GCC 3.4.1 (what's shipped with the latest WinAVR) from sign 
> extending values, let alone producing sane code.
>
> I've tried -Os, -O2, -O3, with and without -fnew-ra... the asm varies, 
> but is generaly crap.
>
> now, if I have:
>     extern char a[4];
>     unsigned long ul;
>
>     ul = ( (unsigned)a[0] << 8 ) | (unsigned)a[1];
>
> why would it be sign extending a[0] and a[1] when they're cast to 
> unsigneds?

a[] is sign extended and the resulting integer interpreted as unsigned.

    extern char a[4];
    unsigned long ul;

    ul = ( (unsigned char)a[0] << 8) | (unsigned char)a[1];