lz-string.js

// Copyright (c) 2013 Pieroxy <pieroxy@pieroxy.net>
// This work is free. You can redistribute it and/or modify it
// under the terms of the WTFPL, Version 2
// For more information see LICENSE.txt or http://www.wtfpl.net/
//
// For more information, the home page:
// http://pieroxy.net/blog/pages/lz-string/testing.html
//
// LZ-based compression algorithm, version 1.4.4
'use strict';
var LZString = (function() {

// private property
var f = String.fromCharCode;
var keyStrBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
var keyStrUriSafe = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-$";
var baseReverseDic = {};

function getBaseValue(alphabet, character) {
  if (!baseReverseDic[alphabet]) {
    baseReverseDic[alphabet] = {};
    for (var i=0 ; i<alphabet.length ; i++) {
      baseReverseDic[alphabet][alphabet.charAt(i)] = i;
    }
  }
  return baseReverseDic[alphabet][character];
}

var LZString = {
  compressToBase64 : function (input) {
    if (input == null) return "";
    var res = LZString._compress(input, 6, function(a){return keyStrBase64.charAt(a);});
    switch (res.length % 4) { // To produce valid Base64
    default: // When could this happen ?
    case 0 : return res;
    case 1 : return res+"===";
    case 2 : return res+"==";
    case 3 : return res+"=";
    }
  },

  decompressFromBase64 : function (input) {
    if (input == null) return "";
    if (input == "") return null;
    return LZString._decompress(input.length, 32, function(index) { return getBaseValue(keyStrBase64, input.charAt(index)); });
  },

  compressToUTF16 : function (input) {
    if (input == null) return "";
    return LZString._compress(input, 15, function(a){return f(a+32);}) + " ";
  },

  decompressFromUTF16: function (compressed) {
    if (compressed == null) return "";
    if (compressed == "") return null;
    return LZString._decompress(compressed.length, 16384, function(index) { return compressed.charCodeAt(index) - 32; });
  },

  //compress into uint8array (UCS-2 big endian format)
  compressToUint8Array: function (uncompressed) {
    var compressed = LZString.compress(uncompressed);
    var buf=new Uint8Array(compressed.length*2); // 2 bytes per character

    for (var i=0, TotalLen=compressed.length; i<TotalLen; i++) {
      var current_value = compressed.charCodeAt(i);
      buf[i*2] = current_value >>> 8;
      buf[i*2+1] = current_value % 256;
    }
    return buf;
  },

  //decompress from uint8array (UCS-2 big endian format)
  decompressFromUint8Array:function (compressed) {
    if (compressed===null || compressed===undefined){
        return LZString.decompress(compressed);
    } else {
        var buf=new Array(compressed.length/2); // 2 bytes per character
        for (var i=0, TotalLen=buf.length; i<TotalLen; i++) {
          buf[i]=compressed[i*2]*256+compressed[i*2+1];
        }

        var result = [];
        buf.forEach(function (c) {
          result.push(f(c));
        });
        return LZString.decompress(result.join(''));

    }

  },


  //compress into a string that is already URI encoded
  compressToEncodedURIComponent: function (input) {
    if (input == null) return "";
    return LZString._compress(input, 6, function(a){return keyStrUriSafe.charAt(a);});
  },

  //decompress from an output of compressToEncodedURIComponent
  decompressFromEncodedURIComponent:function (input) {
    if (input == null) return "";
    if (input == "") return null;
    input = input.replace(/ /g, "+");
    return LZString._decompress(input.length, 32, function(index) { return getBaseValue(keyStrUriSafe, input.charAt(index)); });
  },

  compress: function (uncompressed) {
    return LZString._compress(uncompressed, 16, function(a){return f(a);});
  },
  _compress: function (uncompressed, bitsPerChar, getCharFromInt) {
    if (uncompressed == null) return "";
    var i, value,
        context_dictionary= {},
        context_dictionaryToCreate= {},
        context_c="",
        context_wc="",
        context_w="",
        context_enlargeIn= 2, // Compensate for the first entry which should not count
        context_dictSize= 3,
        context_numBits= 2,
        context_data=[],
        context_data_val=0,
        context_data_position=0,
        ii;

    for (ii = 0; ii < uncompressed.length; ii += 1) {
      context_c = uncompressed.charAt(ii);
      if (!Object.prototype.hasOwnProperty.call(context_dictionary,context_c)) {
        context_dictionary[context_c] = context_dictSize++;
        context_dictionaryToCreate[context_c] = true;
      }

      context_wc = context_w + context_c;
      if (Object.prototype.hasOwnProperty.call(context_dictionary,context_wc)) {
        context_w = context_wc;
      } else {
        if (Object.prototype.hasOwnProperty.call(context_dictionaryToCreate,context_w)) {
          if (context_w.charCodeAt(0)<256) {
            for (i=0 ; i<context_numBits ; i++) {
              context_data_val = (context_data_val << 1);
              if (context_data_position == bitsPerChar-1) {
                context_data_position = 0;
                context_data.push(getCharFromInt(context_data_val));
                context_data_val = 0;
              } else {
                context_data_position++;
              }
            }
            value = context_w.charCodeAt(0);
            for (i=0 ; i<8 ; i++) {
              context_data_val = (context_data_val << 1) | (value&1);
              if (context_data_position == bitsPerChar-1) {
                context_data_position = 0;
                context_data.push(getCharFromInt(context_data_val));
                context_data_val = 0;
              } else {
                context_data_position++;
              }
              value = value >> 1;
            }
          } else {
            value = 1;
            for (i=0 ; i<context_numBits ; i++) {
              context_data_val = (context_data_val << 1) | value;
              if (context_data_position ==bitsPerChar-1) {
                context_data_position = 0;
                context_data.push(getCharFromInt(context_data_val));
                context_data_val = 0;
              } else {
                context_data_position++;
              }
              value = 0;
            }
            value = context_w.charCodeAt(0);
            for (i=0 ; i<16 ; i++) {
              context_data_val = (context_data_val << 1) | (value&1);
              if (context_data_position == bitsPerChar-1) {
                context_data_position = 0;
                context_data.push(getCharFromInt(context_data_val));
                context_data_val = 0;
              } else {
                context_data_position++;
              }
              value = value >> 1;
            }
          }
          context_enlargeIn--;
          if (context_enlargeIn == 0) {
            context_enlargeIn = Math.pow(2, context_numBits);
            context_numBits++;
          }
          delete context_dictionaryToCreate[context_w];
        } else {
          value = context_dictionary[context_w];
          for (i=0 ; i<context_numBits ; i++) {
            context_data_val = (context_data_val << 1) | (value&1);
            if (context_data_position == bitsPerChar-1) {
              context_data_position = 0;
              context_data.push(getCharFromInt(context_data_val));
              context_data_val = 0;
            } else {
              context_data_position++;
            }
            value = value >> 1;
          }


        }
        context_enlargeIn--;
        if (context_enlargeIn == 0) {
          context_enlargeIn = Math.pow(2, context_numBits);
          context_numBits++;
        }
        // Add wc to the dictionary.
        context_dictionary[context_wc] = context_dictSize++;
        context_w = String(context_c);
      }
    }

    // Output the code for w.
    if (context_w !== "") {
      if (Object.prototype.hasOwnProperty.call(context_dictionaryToCreate,context_w)) {
        if (context_w.charCodeAt(0)<256) {
          for (i=0 ; i<context_numBits ; i++) {
            context_data_val = (context_data_val << 1);
            if (context_data_position == bitsPerChar-1) {
              context_data_position = 0;
              context_data.push(getCharFromInt(context_data_val));
              context_data_val = 0;
            } else {
              context_data_position++;
            }
          }
          value = context_w.charCodeAt(0);
          for (i=0 ; i<8 ; i++) {
            context_data_val = (context_data_val << 1) | (value&1);
            if (context_data_position == bitsPerChar-1) {
              context_data_position = 0;
              context_data.push(getCharFromInt(context_data_val));
              context_data_val = 0;
            } else {
              context_data_position++;
            }
            value = value >> 1;
          }
        } else {
          value = 1;
          for (i=0 ; i<context_numBits ; i++) {
            context_data_val = (context_data_val << 1) | value;
            if (context_data_position == bitsPerChar-1) {
              context_data_position = 0;
              context_data.push(getCharFromInt(context_data_val));
              context_data_val = 0;
            } else {
              context_data_position++;
            }
            value = 0;
          }
          value = context_w.charCodeAt(0);
          for (i=0 ; i<16 ; i++) {
            context_data_val = (context_data_val << 1) | (value&1);
            if (context_data_position == bitsPerChar-1) {
              context_data_position = 0;
              context_data.push(getCharFromInt(context_data_val));
              context_data_val = 0;
            } else {
              context_data_position++;
            }
            value = value >> 1;
          }
        }
        context_enlargeIn--;
        if (context_enlargeIn == 0) {
          context_enlargeIn = Math.pow(2, context_numBits);
          context_numBits++;
        }
        delete context_dictionaryToCreate[context_w];
      } else {
        value = context_dictionary[context_w];
        for (i=0 ; i<context_numBits ; i++) {
          context_data_val = (context_data_val << 1) | (value&1);
          if (context_data_position == bitsPerChar-1) {
            context_data_position = 0;
            context_data.push(getCharFromInt(context_data_val));
            context_data_val = 0;
          } else {
            context_data_position++;
          }
          value = value >> 1;
        }


      }
      context_enlargeIn--;
      if (context_enlargeIn == 0) {
        context_enlargeIn = Math.pow(2, context_numBits);
        context_numBits++;
      }
    }

    // Mark the end of the stream
    value = 2;
    for (i=0 ; i<context_numBits ; i++) {
      context_data_val = (context_data_val << 1) | (value&1);
      if (context_data_position == bitsPerChar-1) {
        context_data_position = 0;
        context_data.push(getCharFromInt(context_data_val));
        context_data_val = 0;
      } else {
        context_data_position++;
      }
      value = value >> 1;
    }

    // Flush the last char
    while (true) {
      context_data_val = (context_data_val << 1);
      if (context_data_position == bitsPerChar-1) {
        context_data.push(getCharFromInt(context_data_val));
        break;
      }
      else context_data_position++;
    }
    return context_data.join('');
  },

  decompress: function (compressed) {
    if (compressed == null) return "";
    if (compressed == "") return null;
    return LZString._decompress(compressed.length, 32768, function(index) { return compressed.charCodeAt(index); });
  },

  _decompress: function (length, resetValue, getNextValue) {
    var dictionary = [],
        next,
        enlargeIn = 4,
        dictSize = 4,
        numBits = 3,
        entry = "",
        result = [],
        i,
        w,
        bits, resb, maxpower, power,
        c,
        data = {val:getNextValue(0), position:resetValue, index:1};

    for (i = 0; i < 3; i += 1) {
      dictionary[i] = i;
    }

    bits = 0;
    maxpower = Math.pow(2,2);
    power=1;
    while (power!=maxpower) {
      resb = data.val & data.position;
      data.position >>= 1;
      if (data.position == 0) {
        data.position = resetValue;
        data.val = getNextValue(data.index++);
      }
      bits |= (resb>0 ? 1 : 0) * power;
      power <<= 1;
    }

    switch (next = bits) {
      case 0:
          bits = 0;
          maxpower = Math.pow(2,8);
          power=1;
          while (power!=maxpower) {
            resb = data.val & data.position;
            data.position >>= 1;
            if (data.position == 0) {
              data.position = resetValue;
              data.val = getNextValue(data.index++);
            }
            bits |= (resb>0 ? 1 : 0) * power;
            power <<= 1;
          }
        c = f(bits);
        break;
      case 1:
          bits = 0;
          maxpower = Math.pow(2,16);
          power=1;
          while (power!=maxpower) {
            resb = data.val & data.position;
            data.position >>= 1;
            if (data.position == 0) {
              data.position = resetValue;
              data.val = getNextValue(data.index++);
            }
            bits |= (resb>0 ? 1 : 0) * power;
            power <<= 1;
          }
        c = f(bits);
        break;
      case 2:
        return "";
    }
    dictionary[3] = c;
    w = c;
    result.push(c);
    while (true) {
      if (data.index > length) {
        return "";
      }

      bits = 0;
      maxpower = Math.pow(2,numBits);
      power=1;
      while (power!=maxpower) {
        resb = data.val & data.position;
        data.position >>= 1;
        if (data.position == 0) {
          data.position = resetValue;
          data.val = getNextValue(data.index++);
        }
        bits |= (resb>0 ? 1 : 0) * power;
        power <<= 1;
      }

      switch (c = bits) {
        case 0:
          bits = 0;
          maxpower = Math.pow(2,8);
          power=1;
          while (power!=maxpower) {
            resb = data.val & data.position;
            data.position >>= 1;
            if (data.position == 0) {
              data.position = resetValue;
              data.val = getNextValue(data.index++);
            }
            bits |= (resb>0 ? 1 : 0) * power;
            power <<= 1;
          }

          dictionary[dictSize++] = f(bits);
          c = dictSize-1;
          enlargeIn--;
          break;
        case 1:
          bits = 0;
          maxpower = Math.pow(2,16);
          power=1;
          while (power!=maxpower) {
            resb = data.val & data.position;
            data.position >>= 1;
            if (data.position == 0) {
              data.position = resetValue;
              data.val = getNextValue(data.index++);
            }
            bits |= (resb>0 ? 1 : 0) * power;
            power <<= 1;
          }
          dictionary[dictSize++] = f(bits);
          c = dictSize-1;
          enlargeIn--;
          break;
        case 2:
          return result.join('');
      }

      if (enlargeIn == 0) {
        enlargeIn = Math.pow(2, numBits);
        numBits++;
      }

      if (dictionary[c]) {
        entry = dictionary[c];
      } else {
        if (c === dictSize) {
          entry = w + w.charAt(0);
        } else {
          return null;
        }
      }
      result.push(entry);

      // Add w+entry[0] to the dictionary.
      dictionary[dictSize++] = w + entry.charAt(0);
      enlargeIn--;

      w = entry;

      if (enlargeIn == 0) {
        enlargeIn = Math.pow(2, numBits);
        numBits++;
      }

    }
  }
};
  return LZString;
})();

export { LZString }