[Oberon] System-V - Frame Clipping

[Tomas Kral]

Apologies again, 

> mask := SYSTEM.VAL(SET, ASR(7FFFFFFFH, -(x) ));
> mask := ASR(-{31}, -(x+1))

Above seems same thing, for x := 0..31, I just could not resist testing
it. Will try to understand the code further.

Many thanks.

-- 
Tomas Kral <thomas.kral at email.cz>