scheme48/scheme/sort/visort.scm

;;; The sort package -- stable vector insertion sort	-*- Scheme -*-
;;; Copyright (c) 1998 by Olin Shivers.
;;; This code is open-source; see the end of the file for porting and
;;; more copyright information.
;;; Olin Shivers 10/98.

;;; Exports:
;;; vector-insert-sort  < v [start end] -> vector
;;; vector-insert-sort! < v [start end] -> unspecific
;;;
;;; %vector-insert-sort! is also called from vqsort.scm's quick-sort function.

(define (vector-insert-sort elt< v . maybe-start+end)
  (call-with-values
   (lambda () (vector-start+end v maybe-start+end))
   (lambda (start end)
    (let ((ans (vector-portion-copy v start end)))
      (%vector-insert-sort! elt< ans 0 (- end start))
      ans))))

(define (vector-insert-sort! < v . maybe-start+end)
  (call-with-values
   (lambda () (vector-start+end v maybe-start+end))
   (lambda (start end)
     (%vector-insert-sort! < v start end))))

(define (%vector-insert-sort! elt< v start end)
  (do ((i (+ 1 start) (+ i 1)))	; Invariant: [start,i) is sorted.
      ((>= i end))
    (let ((val (vector-ref v i)))
      (vector-set! v (let lp ((j i))		; J is the location of the
		       (if (<= j start)
			   start	; "hole" as it bubbles down.
			   (let* ((j-1 (- j 1))
				  (vj-1 (vector-ref v j-1)))
			     (cond ((elt< val vj-1)
				    (vector-set! v j vj-1)
				    (lp j-1))
				   (else j)))))
		   val))))

;;; Copyright
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This code is
;;;     Copyright (c) 1998 by Olin Shivers.
;;; The terms are: You may do as you please with this code, as long as
;;; you do not delete this notice or hold me responsible for any outcome
;;; related to its use.
;;;
;;; Blah blah blah. Don't you think source files should contain more lines
;;; of code than copyright notice?


;;; Code tuning & porting
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; This code is tightly bummed as far as I can go in portable Scheme.
;;;
;;; The code can be converted to use unsafe vector-indexing and
;;; fixnum-specific arithmetic ops -- the safety checks done on entry
;;; to VECTOR-INSERT-SORT and VECTOR-INSERT-SORT! are sufficient to
;;; guarantee nothing bad will happen. However, note that if you alter
;;; %VECTOR-INSERT-SORT! to use dangerous primitives, you must ensure
;;; it is only called from clients that guarantee to observe its
;;; preconditions. In the implementation, %VECTOR-INSERT-SORT! is only
;;; called from VECTOR-INSERT-SORT! and the quick-sort code in
;;; vqsort.scm, and the preconditions are guaranteed for these two
;;; clients.  This should provide *big* speedups. In fact, all the
;;; code bumming I've done pretty much disappears in the noise unless
;;; you have a good compiler and also can dump the vector-index checks
;;; and generic arithmetic -- so I've really just set things up for
;;; you to exploit.
;;;
;;; If your Scheme has a faster mechanism for handling optional arguments
;;; (e.g., Chez), you should definitely port over to it. Note that argument
;;; defaulting and error-checking are interleaved -- you don't have to
;;; error-check defaulted START/END args to see if they are fixnums that are
;;; legal vector indices for the corresponding vector, etc.