/usr/share/common-lisp/source/salza2/matches.lisp is in cl-salza2 2.0.9-1.
This file is owned by root:root, with mode 0o644.
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;;; Copyright (c) 2007 Zachary Beane, All Rights Reserved
;;;
;;; Redistribution and use in source and binary forms, with or without
;;; modification, are permitted provided that the following conditions
;;; are met:
;;;
;;; * Redistributions of source code must retain the above copyright
;;; notice, this list of conditions and the following disclaimer.
;;;
;;; * Redistributions in binary form must reproduce the above
;;; copyright notice, this list of conditions and the following
;;; disclaimer in the documentation and/or other materials
;;; provided with the distribution.
;;;
;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;;; ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;;;
(in-package #:salza2)
(defconstant +maximum-match-length+ 258
"The maximum match length allowed.")
(defconstant +maximum-match-distance+ 32768
"The maximum distance for a match.")
(declaim (inline match-length))
(defun match-length (p1 p2 input end)
"Returns the length of the match between positions p1 and p2 in
INPUT; END is a sentinel position that ends the match length
check if reached."
(declare (type input-index p1 p2 end)
(type input-buffer input)
(optimize speed))
(let ((length 0))
(loop
(when (or (/= (aref input p1) (aref input p2))
(= length +maximum-match-length+)
(= p1 end))
(return length))
(setf p1 (logand (1+ p1) #xFFFF)
p2 (logand (1+ p2) #xFFFF)
length (logand #xFFF (1+ length))))))
(defun longest-match (p1 input chains end max-tests)
(declare (type input-index p1 end)
(type input-buffer input)
(type chains-buffer chains)
(type (integer 0 32) max-tests)
(optimize speed))
(let ((match-length 0)
(p2 (aref chains p1))
(test-count 0)
(distance 0))
(declare (type (integer 0 258) match-length)
(type (integer 0 32) test-count))
(loop
(when (or (= match-length +maximum-match-length+)
(= test-count max-tests)
(= p2 p1)
(= p2 (aref chains p2)))
(return (values match-length distance)))
(let ((step (logand (- p1 p2) #xFFFF)))
(when (< +maximum-match-distance+ step)
(return (values match-length distance)))
(let ((possible-length (match-length p1 p2 input end)))
(when (and (< 2 possible-length)
(< match-length possible-length))
(setf distance step
match-length possible-length))
(setf p2 (aref chains p2)))
(incf test-count)))))
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