108 lines
3.3 KiB
Scheme
108 lines
3.3 KiB
Scheme
; Copyright (c) 1993, 1994 Richard Kelsey and Jonathan Rees. See file COPYING.
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;Date: Thu, 4 Nov 93 14:34:04 EST
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;Subject: binary search trees
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;From: kelsey@research.nj.nec.com
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;
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;If you want to add the Hilbert tables I think you should change
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;the name and add some documentation. Neither the name nor the
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;only comment in the file are particulary informative. They are
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;not infinite dimensional vectors, just arbitrarily large one
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;dimensional ones.
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;
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;How about make-big-vector etc.?
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; Hilbert vectors are like vectors that grow as large as they need to.
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; That is, they can be indexed by arbitrarily large nonnegative integers.
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; The implementation allows for arbitrarily large gaps by arranging
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; the entries in a tree.
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; So-called because they live in an infinite-dimensional vector
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; space...
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; ,open bitwise define-record-types
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(define hilbert-log 8)
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(define hilbert-node-size (arithmetic-shift 1 hilbert-log))
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(define hilbert-mask (- hilbert-node-size 1))
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(define minus-hilbert-log (- 0 hilbert-log))
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(define-record-type hilbert :hilbert
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(really-make-hilbert height root)
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(height hilbert-height set-hilbert-height!)
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(root hilbert-root set-hilbert-root!))
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(define (make-hilbert)
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(really-make-hilbert 1 (make-vector hilbert-node-size #f)))
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(define (hilbert-ref hilbert index)
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(let recur ((height (hilbert-height hilbert))
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(index index))
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(if (= height 1)
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(let ((root (hilbert-root hilbert)))
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(if (< index (vector-length root))
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(vector-ref root index)
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#f))
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(let ((node (recur (- height 1)
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(arithmetic-shift index minus-hilbert-log))))
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(if node
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(vector-ref node (bitwise-and index hilbert-mask))
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#f)))))
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(define (hilbert-set! hilbert index value)
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(vector-set!
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(let recur ((height (hilbert-height hilbert))
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(index index))
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(if (= height 1)
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(make-higher-if-necessary hilbert index)
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(let ((index (arithmetic-shift index minus-hilbert-log)))
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(make-node-if-necessary
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(recur (- height 1) index)
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(bitwise-and index hilbert-mask)))))
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(bitwise-and index hilbert-mask)
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value))
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(define (make-higher-if-necessary hilbert index)
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(if (< index hilbert-node-size)
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(hilbert-root hilbert)
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(let ((new-root (make-vector hilbert-node-size #f)))
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(write `(higher ,index)) (newline)
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(vector-set! new-root 0 (hilbert-root hilbert))
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(set-hilbert-root! hilbert new-root)
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(set-hilbert-height! hilbert (+ (hilbert-height hilbert) 1))
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(let ((index (arithmetic-shift index minus-hilbert-log)))
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(make-node-if-necessary (make-higher-if-necessary hilbert index)
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(bitwise-and index hilbert-mask))))))
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(define (make-node-if-necessary node index)
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(or (vector-ref node index)
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(let ((new (make-vector hilbert-node-size #f)))
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;; (write `(wider ,index)) (newline)
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(vector-set! node index new)
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new)))
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; For debugging
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;(define (hilbert->list h)
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; (let recur ((node (hilbert-root h))
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; (height (hilbert-height h))
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; (more '()))
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; (if (= height 0)
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; (if (or node (pair? more))
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; (cons node more)
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; '())
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; (do ((i (- hilbert-node-size 1) (- i 1))
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; (more more (recur (if node
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; (vector-ref node i)
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; #f)
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; (- height 1) more)))
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; ((< i 0) more)))))
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