compress.js

function writeVL4(arr, num) {
  var halfByte;
  do {
    halfByte = num & 7;
    num >>= 3;
    if(num !== 0)
      halfByte |= 8;
    arr.push(halfByte);
  } while (num !== 0)
}

function scanVL4(arr, ptr, refNum) {
  var halfByte;
  var len = 0;
  var num = 0;
  do {
    halfByte = arr[ptr];
    if(halfByte === void 0)
      return null; // error
      //throw 4;
    num |= (halfByte & 7) << (len * 3);
    if((halfByte & 8) === 8)
      len++;
    ptr++;
  } while ((halfByte & 8) === 8)
  if(len > 0 && num < 8)
    return -1;
  else {
    refNum[0] = num;
    return ptr;
  }
}

var base67 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_+=@"; // 67*67 < 16*16*16 + 16*16 + 16
var base67rev = (function() {
  var rev = {};
  for(var i=0; i<base67.length; i++) {
    rev[base67[i]] = i;
  }
  return rev;
})();

function keysEncode(keys) {
  var lastFrame = 0;
  var lastKeys = 0;
  var arrHB = [];
  var arrBase67 = [];
  var curFrame, curKeys;
  for(var i in keys) {
    curFrame = +i;
    curKeys = keys[i];
    for(var xhb=0; xhb<18; xhb++) {
      if((curKeys ^ lastKeys) & (1 << xhb)) {
        writeVL4(arrHB, curFrame - lastFrame);
        writeVL4(arrHB, xhb);
        // console.log("df:", curFrame - lastFrame, ", key:", xhb, i)
        lastFrame = curFrame;
      }
    }
    lastKeys = curKeys;
  }
  arrHB.push(8);
  arrHB.push(0);
  
  // console.log(arrHB);
  
  var nHB = arrHB.length;
  var sum;
  for(var ptr=0; ptr<nHB; ptr+=3) {
    if(nHB - ptr >= 3) {
      sum = (arrHB[ptr] + arrHB[ptr+1]*16 + arrHB[ptr+2]*16*16);
    } else if(nHB - ptr == 2) {
      sum = (arrHB[ptr] + arrHB[ptr+1]*16 + 16*16*16);
    } else if(nHB - ptr == 1) {
      sum = (arrHB[ptr] + 16*16 + 16*16*16);
    }
    //console.log(sum);
    arrBase67.push(base67[sum%67] + base67[~~(sum/67)]);
  }
  
  return arrBase67.join("");
}

function keysDecode(str) {
  var lastFrame = 0;
  var lastKeys = 0;
  var keys = {};
  var arrHB = [];
  var arrBase67 = [];
  var objNum = [0]; // pass by reference
  
  if(str.length%2 !== 0)
    return null;
  
  for(var ptr=0; ptr<str.length; ptr+=2) {
    var lo67 = base67rev[str[ptr]], hi67 = base67rev[str[ptr+1]];
    //console.log(lo67 + " " + hi67 + " " + (lo67 + hi67 * 67));
    if((lo67 === void 0) || (hi67 === void 0))
      return null;
      //throw 1;
    arrBase67.push(lo67 + hi67 * 67);
  }
  
  for(var i=0; i<arrBase67.length; i++) {
    var data = arrBase67[i];
    //console.log(data);
    if(data < 16*16*16) {
      arrHB.push(data & 15); data >>= 4;
      arrHB.push(data & 15); data >>= 4;
      arrHB.push(data & 15);
    } else if(data < 16*16*16 + 16*16) {
      data -= 16*16*16;
      arrHB.push(data & 15); data >>= 4;
      arrHB.push(data & 15);
    } else if(data < 16*16*16 + 16*16 + 16) {
      data -= 16*16*16 + 16*16;
      arrHB.push(data & 15);
    } else {
      //return null;
      throw 2;
    }
  }
  
  //console.log(arrHB.length, arrHB.toString());
  
  for(var i=0; i<arrHB.length;) {
    var nexti,dframe,bit;
    nexti = scanVL4(arrHB, i, objNum);
    if(nexti === null) {
      console.log("scanVL4 null:",i,arrHB.length);
      throw 3;
    }
    if(nexti === -1)
      break;
    dframe = objNum[0];
    i = nexti;
    nexti = scanVL4(arrHB, i, objNum);
    if(nexti === null) {
      console.log("scanVL4 null:",i,arrHB.length);
      throw 4;
    }
    if(nexti === -1)
      throw 5;
    bit = objNum[0];
    i = nexti;
    lastFrame += dframe;
    lastKeys ^= (1 << bit); // flip that bit
    keys[lastFrame] = lastKeys;
    // console.log("df:",dframe,", key:", bit);
  }
  
  return keys;
}