script-fu error.
Quoting Kevin Cozens :
Giovanni Rizzardi wrote:
I'm trying to update an old script (stegano.scm) that uses the functions
bit-or and bit-and. Both these function should be
ported from SIOD to TinyScheme but the interpreter raises an exception
complaining about an "unbound variable".
Those two functions are unique to SIOD. TinyScheme tends to follow the R4RS
and R5RS Scheme standards which do not currently define bit wise operations.
The bitwise operation could be written in standard Scheme but they would be
rather slow.
Bit operations were proposed in SRFI-33 (http://srfi.schemers.org/srfi-33/)
but that is currently in a withdrawn state awaiting revival. You could check
to see if they have a reference implementation which you could use.
I don't know if they are reference implementations, but the following
two functions should work for reasonably-sized positive integers.
(define (bit-or x y)
(cond
((= x y) x)
((zero? x) y)
((zero? y) x)
(else
(+ (* (bit-or (quotient (trunc x) 2) (quotient (trunc y) 2)) 2)
(if (and (even? x) (even? y)) 0 1)))))
(define (bit-and x y)
(cond
((= x y) x)
((zero? x) 0)
((zero? y) 0)
(else
(+ (* (bit-and (quotient (trunc x) 2) (quotient (trunc y) 2)) 2)
(if (or (even? x) (even? y)) 0 1)))))
