zobrist-hashing

What is this?

See http://en.wikipedia.org/wiki/Zobrist_hashing Note: This is for Go only.

 ;Requires SRFI 27 and SRFI 60 
 (define last-hash '()) 
 (define limit 79228162514264337593543950336) 
 ;;Maximum 96 bit number for collision resistance. 
  
 (define white-rep (random-integer limit)) 
 (define black-rep (random-integer limit)) 
 (define ko-rep (random-integer limit)) 
 (define empty-rep (random-integer limit)) 
 (define (zobrist-hash go-position-table) 
   (let ((create-zobrist-hash 
          (iterate-zobrist-hash white-rep 
                                black-rep 
                                ko-rep 
                                empty-rep 
                                go-position-table))) 
     (if (number? last-hash) 
         (begin 
           (set! last-hash 
                 (bitwise-xor 
                  last-hash 
                  create-zobrist-hash)) 
           (display last-hash)) 
           (begin 
       (set! last-hash create-zobrist-hash) 
       create-zobrist-hash)))) 
 (define (iterate-zobrist-hash white black ko open go-position-table) 
   (apply bitwise-xor 
          (letrec 
              ((iter 
                (lambda (go-position-table) 
                  (cond 
                   ((null? go-position-table) '()) 
                   ((number? (car go-position-table)) 
                    (cond 
                     ((eq? (car go-position-table) 0) 
                      (cons 
                       open (iter (cdr go-position-table)))) 
                     ((eq? (car go-position-table) 1) 
                      (cons white 
                            (iter (cdr go-position-table)))) 
                     ((eq?  (car go-position-table) 2) 
                      (cons black 
                            (iter (cdr go-position-table)))) 
                     ((eq? (car go-position-table) 3) 
                      (cons ko 
                            (iter (cdr go-position-table)))))))))) 
            (iter go-position-table)))) 

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