在JavaScript中使用整数作为位字段

1. 迭代数组时不要使用“for(varx in y)”类型的循环。始终使用索引。

2. 最后添加到位域字符串的内容并不总是表示原始字符串的15位数字。“get”函数始终假定每个位域组件具有相同的位数。

3. 你漏掉了 var

这是我的版本,它至少适用于您的示例输入:

  makeBuildBitfield: function(build) {
    var b = build.split('');
    var f = [3, 0]; // the "3" is there for future purposes
    var i = 1, j = 0;;

    for (var t = 0; t < b.length; ++t, ++j) {
        if (j === 15) {
          f[++i] = 0;
          j = 0;
        }
        f[i] = (f[i] << 2) + (b[t] & 3);
    }

    f[0] = j === 0 ? 15 : j;
    return f.join('.');
  },

  getBuildFromBitfield: function(bitfield) {
    var b = bitfield.split('.');

    var ba = [];
    for (var x = 1; x < b.length; ++x) { //start from 1 to skip the "3"
        ba[x] = [];
        var n = b[x];
        for (var y = (x === b.length - 1 ? parseInt(b[0], 10) : 15); --y >= 0; ) {
            ba[x][y] = n & 3;
            n = n >>> 2;
        }
    }

    var build = '';
    for (var a = 1; a < ba.length; ++a) {
      build += ba[a].join('');
    }
    return build;
  }

这里有一个很好的简短的方法,可以将位字段缩小到base-36字符串。它也适用于以10为基数的字符串,但这是一个更精简的。它也适用于位字段中的前导零。

function shrink (s) {
  for (var p=0, l=s.length, r=''; p<l; p+=25) { 
    r+=parseInt('1'+s.substring(p,p+25),4).toString(36); 
  }
  return r;
}

function expand (s) {
  for (var p=0, l=s.length, r=''; p<l; p+=10) { 
    r+=parseInt(s.substring(p,p+10), 36).toString(4).substring(1);
  }
  return r;
}

编辑-我假设您的目标是收缩位字段,通过url(GET请求)发送它,然后在另一侧展开它。这将允许您这样做,尽管除了传输和扩展数据之外,您将无法对收缩的数据做任何有用的事情。

编辑2-这现在是一个“无点”的变化。下面是一个测试:

var bits =  "0000000000000000000000000000000032222000" +
            "0000000000000000000000000000000031111300" +
            "0000000000000000000002111300000002111200" +
            "0000000000000000000003111120000003111130" +
            "0000000000000000000000021111200000111120" +
            "0000000000000320000000000211112000311110" +
            "0000000000002111123000000031111130011113" +
            "0000000000000321111111230000311112031111" +
            "0000000000000000032111111123002112200000" +
            "0000000032223300000000021111112000000000" +
            "0000000021111111112233000332130000000000" +
            "0330000000033322111111111111003330000000" +
            "2112000000000000000003222112001113000000" +
            "2112000111111111111112222220001113000000" +
            "2112000222222111111111111120001113000000" +
            "2112000000000000000033222230001113000000" +
            "2112003111111111111111111120001113000000" +
            "2112000000000000000000000000001113000000" +
            "2112333333333333333333333333331113000000" +
            "2111111111111111111111111111111113000000" ;

var shrunk = shrink(bits);
// b33j9ynrb4b34c70cb9cb33j9ynrclf2iv9lsx6ocpgnayh8n4b33j9ys...

var restored = expand(shrunk);

alert ( "Worked: " + (bits===restored) + ", orig size: " 
      + bits.length + ", shrunk size: " + shrunk.length);

// Worked: true, orig size: 800, shrunk size: 320

位图.js

function Bitmap (vals) {
  this.arr = [];
  this.length = 0;
  if (vals) {
    for (var i = vals.length - 1; i >= 0; --i) {
      if (vals [i]) {
        this.set (i);
      }
      else {
        this.clear (i);
      }
    }
  }
}

Bitmap.prototype = {
    constructor: Bitmap

  , toString: function () {
      vals = [];
      for (var i = this.length - 1; i >= 0; --i) {
        vals [i] = this.get (i) ? "1" : "0";
      }
      return vals.join ("");
    }

  , clear: function (i) {
      if (i >= this.length) {
        this.length = i + 1;
      }
      var pos = i / 32 | 0;
      this.arr [pos] = this.arr [pos] & ~(1 << i % 32);
    }

  , get: function (i) {
      return (this.arr [Math.floor (i / 32 | 0)] & 1 << i % 32) > 0;
    }

  , serialize: function () {
      var str = "";
      for (var i = 0; i < this.arr.length; ++i) {
        var num = this.arr [i];
        str += num < 0
          ? (-num).toString (36) + Bitmap.NEGATIVE_DELIM
          : num.toString (36) + Bitmap.POSITIVE_DELIM
          ;
      }
      var trailingLength = this.length % 32;
      if (trailingLength == 0) {
        trailingLength = 32;
      }
      if (this.length == 0) {
        trailingLength = 0;
      }
      return str + trailingLength.toString (36);
    }

  , set: function (i) {
      if (i >= this.length) {
        this.length = i + 1;
      }
      var pos = i / 32 | 0;
      this.arr [pos] = this.arr [pos] | 1 << i % 32;
    }

  , size: function () {
      return this.length;
    }

};

Bitmap.POSITIVE_DELIM = ".";
Bitmap.NEGATIVE_DELIM = "!"

Bitmap.deserialize = (function () {
  var MATCH_REGEX = new RegExp (
      "[A-Za-z0-9]+(?:"
      + Bitmap.POSITIVE_DELIM
      + "|"
      + Bitmap.NEGATIVE_DELIM
      + ")?"
    , "g");
  return function (str) {
    var bm = new Bitmap ();
    var arr = str.match (MATCH_REGEX);
    var trailingLength = parseInt (arr.pop (), 36);
    for (var i = 0; i < arr.length; ++i) {
      var str = arr [i];
      var sign = str.charAt (str.length - 1) == Bitmap.POSITIVE_DELIM ? 1 : -1;
      bm.arr [i] = parseInt (str, 36) * sign;
    }
    bm.length = Math.max ((arr.length - 1) * 32 + trailingLength, 0);
    return bm;
  };
}) ();

测试.js

function toBits (numStr, numBitsToExtract) {
  var numChars = numStr.split ("");
  var bits = [];
  for (var i = 0; i < numChars.length; ++i) {
    var num = numChars [i] - 0;
    for (var j = numBitsToExtract - 1; j >= 0; --j) {
      bits.push (num & 1 << j ? 1 : 0);
    }
  }
  return bits;
}

function fromBits (bitStr, numBitsToExtract) {
  var bitChars = bitStr.split ("");
  var nums = [];
  for (var i = 0; i < bitChars.length; ) {
    var num = 0;
    for (var j = numBitsToExtract - 1; j >= 0; ++i, --j) {
      num |= bitChars [i] - 0 << j;
    }
    nums.push (num);
  }
  return nums.join ("");
}

var numStr = "2030000000000000000030000000000000000003333212111221121301";
var bits = toBits (numStr, 2);
var serialized = new Bitmap (bits).serialize (); // "1d.lc.ou00e8!ci3a.k"
var recoveredNumStr = fromBits (Bitmap.deserialize (serialized).toString (), 2);