javascript lz77 compression

// This class provides simple LZ77 compression and decompression.
// https://github.com/olle/lz77-kit
// https://raw.github.com/olle/lz77-kit/master/src/main/js/lz77.js

/*
compressor = new LZ77();
var c= compressor.compress("abcacdacdcdacdacdadcadcda");
compressor.decompress(c);
*/


var LZ77 = function (settings) {

    settings = settings || {};

    // PRIVATE

    var referencePrefix = "`";
    var referenceIntBase = settings.referenceIntBase || 96;
    var referenceIntFloorCode = " ".charCodeAt(0);
    var referenceIntCeilCode = referenceIntFloorCode + referenceIntBase - 1;
    var maxStringDistance = Math.pow(referenceIntBase, 2) - 1;
    var minStringLength = settings.minStringLength || 5;
    var maxStringLength = Math.pow(referenceIntBase, 1) - 1 + minStringLength;
    var defaultWindowLength = settings.defaultWindowLength || 144;
    var maxWindowLength = maxStringDistance + minStringLength;

    var encodeReferenceInt = function (value, width) {
        if ((value >= 0) && (value < (Math.pow(referenceIntBase, width) - 1))) {
            var encoded = "";
            while (value > 0) {
                encoded = (String.fromCharCode((value % referenceIntBase) + referenceIntFloorCode)) + encoded;
                value = Math.floor(value / referenceIntBase);
            }
            var missingLength = width - encoded.length;
            for (var i = 0; i < missingLength; i++) {
                encoded = String.fromCharCode(referenceIntFloorCode) + encoded;
            }
            return encoded;
        } else {
            throw "Reference int out of range: " + value + " (width = " + width + ")";
        }
    };

    var encodeReferenceLength = function (length) {
        return encodeReferenceInt(length - minStringLength, 1);
    };

    var decodeReferenceInt = function (data, width) {
        var value = 0;
        for (var i = 0; i < width; i++) {
            value *= referenceIntBase;
            var charCode = data.charCodeAt(i);
            if ((charCode >= referenceIntFloorCode) && (charCode <= referenceIntCeilCode)) {
                value += charCode - referenceIntFloorCode;
            } else {
                throw "Invalid char code in reference int: " + charCode;
            }
        }
        return value;
    };

    var decodeReferenceLength = function (data) {
        return decodeReferenceInt(data, 1) + minStringLength;
    };

    // PUBLIC

    /**
     * Compress data using the LZ77 algorithm.
     *
     * @param data
     * @param windowLength
     */
    this.compress = function (data, windowLength) {
        windowLength = windowLength || defaultWindowLength;
        if (windowLength > maxWindowLength) {
            throw "Window length too large";
        }
        var compressed = "";
        var pos = 0;
        var lastPos = data.length - minStringLength;
        while (pos < lastPos) {
            var searchStart = Math.max(pos - windowLength, 0);
            var matchLength = minStringLength;
            var foundMatch = false;
            var bestMatch = {distance:maxStringDistance, length:0};
            var newCompressed = null;
            while ((searchStart + matchLength) < pos) {
                var isValidMatch = ((data.substr(searchStart, matchLength) == data.substr(pos, matchLength)) && (matchLength < maxStringLength));
                if (isValidMatch) {
                    matchLength++;
                    foundMatch = true;
                } else {
                    var realMatchLength = matchLength - 1;
                    if (foundMatch && (realMatchLength > bestMatch.length)) {
                        bestMatch.distance = pos - searchStart - realMatchLength;
                        bestMatch.length = realMatchLength;
                    }
                    matchLength = minStringLength;
                    searchStart++;
                    foundMatch = false;
                }
            }
            if (bestMatch.length) {
                newCompressed = referencePrefix + encodeReferenceInt(bestMatch.distance, 2) + encodeReferenceLength(bestMatch.length);
                pos += bestMatch.length;
            } else {
                if (data.charAt(pos) != referencePrefix) {
                    newCompressed = data.charAt(pos);
                } else {
                    newCompressed = referencePrefix + referencePrefix;
                }
                pos++;
            }
            compressed += newCompressed;
        }
        return compressed + data.slice(pos).replace(/`/g, "``");
    };

    /**
     * Decompresses LZ77 compressed data.
     *
     * @param data
     */
    this.decompress = function (data) {
        var decompressed = "";
        var pos = 0;
        while (pos < data.length) {
            var currentChar = data.charAt(pos);
            if (currentChar != referencePrefix) {
                decompressed += currentChar;
                pos++;
            } else {
                var nextChar = data.charAt(pos + 1);
                if (nextChar != referencePrefix) {
                    var distance = decodeReferenceInt(data.substr(pos + 1, 2), 2);
                    var length = decodeReferenceLength(data.charAt(pos + 3));
                    decompressed += decompressed.substr(decompressed.length - distance - length, length);
                    pos += minStringLength - 1;
                } else {
                    decompressed += referencePrefix;
                    pos += 2;
                }
            }
        }
        return decompressed;
    };
};