Hi, Marcel,
as a first installment on earlier promises, here are
the inverse functions as GForth code:
include random.fs \ need 'rnd' for test
variable (rnd) \ for marcel's rnd
\ note: for "dup shift xor," all the inverse functions
\ start with the original functions
: turn-around ( n -- n' ) dup 5 lshift xor ;
: -turn-around ( n -- n' ) turn-around
dup 10 lshift xor dup 20 lshift xor ;
: take-off2nd ( n -- n' ) dup 17 rshift xor ;
: -take-off2nd ( n -- n' ) take-off2nd ;
: take-off1st ( n -- n' ) dup 13 lshift xor ;
: -take-off1st ( n -- n' ) take-off1st dup 26 lshift xor ;
\ note: here we reverse order for inverses because
\ the lshifts and rshift don't commute
: take-off ( n -- n' ) take-off1st take-off2nd ;
: -take-off ( n -- n' ) -take-off2nd -take-off1st ;
: marcel ( -- n ) (rnd) @ take-off dup turn-around (rnd) ! ;
: -marcel ( -- n ) (rnd) @ -turn-around dup -take-off (rnd) ! ;
: tst begin cr rnd ( <-<< time based random number ) dup .
(rnd) ! marcel dup . -take-off . -marcel .
\ the check is 1st# = 3rd# and 2nd# = 4th#
key 10 = until ;
