Quoting Kevin Cozens <kevin@xxxxxxxxx>: > 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 but that is currently in a withdrawn state awaiting revival.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))))) _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
