Add insertion-sort.

insertion-sort.lisp

@@ -0,0 +1,51 @@
+;;;; Copyright (c) 2012 Jorge Tavares <jorge.tavares@ieee.org>
+;;;;
+;;;; Permission is hereby granted, free of charge, to any person obtaining
+;;;; a copy of this software and associated documentation files (the
+;;;; "Software"), to deal in the Software without restriction, including
+;;;; without limitation the rights to use, copy, modify, merge, publish,
+;;;; distribute, sublicense, and/or sell copies of the Software, and to
+;;;; permit persons to whom the Software is furnished to do so, subject to
+;;;; the following conditions:
+;;;;
+;;;; The above copyright notice and this permission notice shall be included
+;;;; in all copies or substantial portions of the Software.
+;;;;
+;;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+;;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+;;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+;;;; IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+;;;; CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+;;;; TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+;;;; SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+(in-package :usort)
+
+;;;
+;;; insertion sort
+;;;
+
+(defun insertion-sort  (sequence predicate &key key)
+  (%insertion-sort sequence 0 (length sequence) predicate (or key #'identity))
+  sequence)
+
+(defun %insertion-sort (sequence start end predicate key)
+  (declare (type function predicate key)
+	   (type fixnum start end)
+	   (type simple-vector sequence)
+	   (optimize (speed 3) (safety 0)))
+  ;; the start arg is actually not necessary but it is included
+  ;; to facilitate the use of insertion sort in other sorting 
+  ;; algorithms like quicksort with insertion for small values
+  (loop for j from (1+ start) below end 
+	do (let* ((pivot (aref sequence j))
+		  (data (funcall key pivot))
+		  (i (1- j)))
+	     (declare (type fixnum i))
+	     (loop while (and (>= i start) 
+			      (funcall predicate data (funcall key (aref sequence i))))
+		   do (setf (aref sequence (1+ i)) (aref sequence i)
+			    i (1- i)))
+	     (setf (aref sequence (1+ i)) pivot))))
+
+

packages.lisp

@@ -23,5 +23,6 @@
   (:use :cl)
   (:documentation "Portable and optimized sorting algorithms.")
   (:export 
+   #:insertion-sort
    #:quicksort
    ))

quicksort.lisp

@@ -34,9 +34,15 @@
 	   (type function predicate key)
 	   (type simple-vector sequence)
 	   (optimize (speed 3) (safety 0)))
+  ;; the while loop avoids the second recursive call 
+  ;; to quicksort made at the end of the loop body 
   (loop while (< start end)
 	do (let* ((i start)
 		  (j (1+ end))
+		  ;; the pivot is chosen with an adapted median-of-3 method
+		  ;; instead of picking 3 random numbers and use the middle
+		  ;; value, the pivot is picked by the median of start and
+		  ;; end. this way we avoid the use of the random generator
 		  (p (+ start (ash (- end start) -1)))
 		  (x (aref sequence p)))
 	     (declare (fixnum i j p))
@@ -56,6 +62,8 @@
 		 (rotatef (aref sequence i) (aref sequence j))))
 	     (setf (aref sequence start) (aref sequence j)
 		   (aref sequence j) x)
+	     ;; check each partition is smaller and pick the smallest one
+	     ;; this way the stack depth worst-case is Theta(lgn)
 	     (if (< (- j start) (- end j))
 		 (progn 
 		   (%quicksort sequence start (1- j) predicate key)
@@ -64,5 +72,3 @@
 		   (%quicksort sequence (1+ j) end predicate key)
 		   (setf end (1- j)))))))
 
-
-

usort.asd

@@ -25,7 +25,8 @@
     :author "Jorge Tavares <jorge.tavares@ieee.org>"  
     :licence "MIT"  
     :serial t
-    :components ((:file "packages")  
+    :components ((:file "packages") 
+		 (:file "insertion-sort")
 		 (:file "quicksort")
 		 (:static-file "README")
 		 (:static-file "LICENSE")))