38 lines
1.1 KiB
Scheme
38 lines
1.1 KiB
Scheme
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; Copyright (c) 1993-1999 by Richard Kelsey. See file COPYING.
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; Sets of integers implemented as integers.
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(define (make-empty-integer-set)
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0)
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(define (add-to-integer-set set integer)
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(bitwise-ior set (arithmetic-shift 1 integer)))
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(define integer-set-chunk-size 24)
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(define word-mask (- (arithmetic-shift 1 integer-set-chunk-size) 1))
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; The nested loop reduces the amount of bignum arithmetic needed (and reduces
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; the time by as much as a factor of 10).
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(define (map-over-integer-set proc set)
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(do ((set set (arithmetic-shift set (- integer-set-chunk-size)))
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(i 0 (+ i integer-set-chunk-size))
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(l '() (do ((set (bitwise-and set word-mask) (arithmetic-shift set -1))
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(j 0 (+ j 1))
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(l l (if (odd? set)
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(cons (proc (+ i j)) l)
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l)))
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((or (= 0 set) (>= j integer-set-chunk-size))
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l))))
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((= 0 set)
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(reverse l))))
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(define integer-set-and bitwise-and)
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(define integer-set-ior bitwise-ior)
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(define integer-set-not bitwise-not)
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(define (integer-set-subtract set1 set2)
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(bitwise-and set1 (bitwise-not set2)))
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(define integer-set-equal? =)
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