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; Copyright (c) 1993-2008 by Richard Kelsey. See file COPYING.
; Sets of integers implemented as integers.
(define (make-empty-integer-set)
0)
(define (add-to-integer-set set integer)
(bitwise-ior set (arithmetic-shift 1 integer)))
(define integer-set-chunk-size 24)
(define word-mask (- (arithmetic-shift 1 integer-set-chunk-size) 1))
; The nested loop reduces the amount of bignum arithmetic needed (and reduces
; the time by as much as a factor of 10).
(define (map-over-integer-set proc set)
(do ((set set (arithmetic-shift set (- integer-set-chunk-size)))
(i 0 (+ i integer-set-chunk-size))
(l '() (do ((set (bitwise-and set word-mask) (arithmetic-shift set -1))
(j 0 (+ j 1))
(l l (if (odd? set)
(cons (proc (+ i j)) l)
l)))
((or (= 0 set) (>= j integer-set-chunk-size))
l))))
((= 0 set)
(reverse l))))
(define integer-set-and bitwise-and)
(define integer-set-ior bitwise-ior)
(define integer-set-not bitwise-not)
(define (integer-set-subtract set1 set2)
(bitwise-and set1 (bitwise-not set2)))
(define integer-set-equal? =)
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