LZString Compressor Web Worker

gistfile1.js

var compress = function (uncompressed) {
  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_string="",
      context_data_val=0,
      context_data_position=0,
      ii,
      f=String.fromCharCode;

  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 == 15) {
              context_data_position = 0;
              context_data_string += f(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 == 15) {
              context_data_position = 0;
              context_data_string += f(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 == 15) {
              context_data_position = 0;
              context_data_string += f(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 == 15) {
              context_data_position = 0;
              context_data_string += f(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 == 15) {
            context_data_position = 0;
            context_data_string += f(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 == 15) {
            context_data_position = 0;
            context_data_string += f(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 == 15) {
            context_data_position = 0;
            context_data_string += f(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 == 15) {
            context_data_position = 0;
            context_data_string += f(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 == 15) {
            context_data_position = 0;
            context_data_string += f(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 == 15) {
          context_data_position = 0;
          context_data_string += f(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 == 15) {
      context_data_position = 0;
      context_data_string += f(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 == 15) {
      context_data_string += f(context_data_val);
      break;
    }
    else context_data_position++;
  }
  return context_data_string;
}

var decompress = function (compressed) {
  if (compressed == null) return "";
  if (compressed == "") return null;
  var dictionary = [],
      next,
      enlargeIn = 4,
      dictSize = 4,
      numBits = 3,
      entry = "",
      result = "",
      i,
      w,
      bits, resb, maxpower, power,
      c,
      f = String.fromCharCode,
      data = {string:compressed, val:compressed.charCodeAt(0), position:32768, 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 = 32768;
      data.val = data.string.charCodeAt(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 = 32768;
            data.val = data.string.charCodeAt(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 = 32768;
            data.val = data.string.charCodeAt(data.index++);
          }
          bits |= (resb>0 ? 1 : 0) * power;
          power <<= 1;
        }
      c = f(bits);
      break;
    case 2:
      return "";
  }
  dictionary[3] = c;
  w = result = c;
  while (true) {
    if (data.index > data.string.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 = 32768;
        data.val = data.string.charCodeAt(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 = 32768;
            data.val = data.string.charCodeAt(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 = 32768;
            data.val = data.string.charCodeAt(data.index++);
          }
          bits |= (resb>0 ? 1 : 0) * power;
          power <<= 1;
        }
        dictionary[dictSize++] = f(bits);
        c = dictSize-1;
        enlargeIn--;
        break;
      case 2:
        return result;
    }

    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 += 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++;
    }

  }
}

this.addEventListener('message', function(event) {
  if (event.data.type === "compress") {
    postMessage({url: event.data.url, chunk: compress(event.data.chunk)});
  } else if (event.data.type === "decompress") {
    postMessage({url: event.data.url, chunk: decompress(event.data.chunk)});
  }
}, false);