57 lines
1.5 KiB
Scheme
57 lines
1.5 KiB
Scheme
(define (vector-portion-copy vec start end)
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(let* ((len (vector-length vec))
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(new-len (- end start))
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(new (make-vector new-len)))
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(do ((i start (+ i 1))
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(j 0 (+ j 1)))
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((= i end) new)
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(vector-set! new j (vector-ref vec i)))))
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(define (vector-copy vec)
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(vector-portion-copy vec 0 (vector-length vec)))
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(define (vector-portion-copy! target src start end)
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(let ((len (- end start)))
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(do ((i (- len 1) (- i 1))
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(j (- end 1) (- j 1)))
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((< i 0))
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(vector-set! target i (vector-ref src j)))))
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(define (has-element list index)
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(cond
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((zero? index)
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(if (pair? list)
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(values #t (car list))
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(values #f #f)))
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((null? list)
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(values #f #f))
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(else
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(has-element (cdr list) (- index 1)))))
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(define (list-ref-or-default list index default)
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(call-with-values
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(lambda () (has-element list index))
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(lambda (has? maybe)
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(if has?
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maybe
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default))))
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(define (vector-start+end vector maybe-start+end)
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(let ((start (list-ref-or-default maybe-start+end
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0 0))
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(end (list-ref-or-default maybe-start+end
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1 (vector-length vector))))
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(values start end)))
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(define (vectors-start+end-2 vector-1 vector-2 maybe-start+end)
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(let ((start-1 (list-ref-or-default maybe-start+end
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0 0))
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(end-1 (list-ref-or-default maybe-start+end
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1 (vector-length vector-1)))
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(start-2 (list-ref-or-default maybe-start+end
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2 0))
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(end-2 (list-ref-or-default maybe-start+end
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3 (vector-length vector-2))))
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(values start-1 end-1
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start-2 end-2)))
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