A class for bitfields

// A bitfield represents a binary number of arbitrary length
// This implementation requires the JavaScript Uint32Array data type
function BitField(length,data) {
  if (length instanceof BitField) {
    this.length    = length.length
    this.maxIndex  = length.maxIndex
    this.maxMask   = length.maxMask
    this.maxPlaces = length.maxPlaces
    this.data      = Uint32Array.from(length.data)
  }
  else {
    this.length = length
    this.maxIndex  = ( ~~(length/32) + (length % 32 && 1) ) - 1
    this.maxMask   = length % 32 ? (1 << length % 32) - 1 : 0xffffffff
    this.maxPlaces = length % 32 || 32
    if (data) {
      if (data instanceof Uint32Array)
        this.data = data
      else if (data instanceof Array) {
        this.data = Uint32Array.from(data)
      }
      else if (typeof data == "number") {
        this.data = new Uint32Array( this.maxIndex + 1 )
        this.data[0] = data
      }
    }
    else
      this.data = new Uint32Array( this.maxIndex + 1 )
  }
}
BitField.prototype.get = function(pos) {
  return ( this.data[~~(pos/32)] & (1 << (pos % 32) ) ) && 1
}
BitField.prototype.set = function(pos) {
  this.data[~~(pos/32)] |= ( 1 << (pos % 32))
}
BitField.prototype.unset = function(pos) {
  this.data[~~(pos/32)] &= ~( 1 << (pos % 32))
}
BitField.prototype.clear = function() {
  this.data.fill(0)
}
BitField.prototype.increment = function() {
  for (var i=0;i<this.maxIndex;i++) {
    if (this.data[i] != 0xffffffff) {
      this.data[i]++
      return true
    }
    else {
      this.data[i] = 0
    }
  }
  if (this.data[this.maxIndex] != this.maxMask) {
    this.data[this.maxIndex]++
    return true
  }
  else {
    return false // Maximum reached
  }
}
BitField.prototype.equals = function(bf) {
  if (this.length != bf.length) return false
  for (var i=0;i<this.maxIndex;i++) {
    if (this.data[i] != bf.data[i]) return false;
  }
  return (((this.data[this.maxIndex]^bf.data[this.maxIndex])&this.maxMask)==0)
}

BitField.prototype.toString = function() {
  return pad((this.data[this.maxIndex]&this.maxMask).toString(2),this.maxPlaces) +
        this.data.slice(0,this.data.length-1).reverse().map(function(i){
         return pad(i.toString(2),32)
        }).join("")
  function pad(s,k) {
    return ("00000000000000000000000000000000"+s).slice(-k)
  }
}

/* Some additions for retarded browsers
   The implementations do not pretend to be fully-featured
   They are just enough to make the class BitField usable in older browsers */

if (!Uint32Array.from) {
  Uint32Array.from = function(array) {
    var result = new Uint32Array(array.length)
    for (var i=0;i<array.length;i++) result[i] = array[i]
    return result
  }
}
if (!Array.prototype.fill) {
  Array.prototype.fill = function(value) {
    for (var i=0;i<this.length;i++) this[i] = value
    return this
  }
}
if (!Uint32Array.prototype.slice) {
  Uint32Array.prototype.slice = function(i1,i2) {
    var result = new Uint32Array(i2-i1)
    for (var i=i1;i<i2;i++) result[i-i1] = this[i]
    return result
  }
}
if (!Uint32Array.prototype.reverse) {
  Uint32Array.prototype.reverse = function() {
    var len = this.length
    var result = new Uint32Array(len)
    for (var i=0;i<len;i++) result[i]=this[len-i-1]
    return result
  }
}
if (!Uint32Array.prototype.map) {
  Uint32Array.prototype.map = function(f) {
    var len = this.length
    var result = new Uint32Array(len)
    for (var i=0;i<len;i++) result[i] = f(this[i])
    return result
  }
}
if (!Uint32Array.prototype.join) {
  Uint32Array.prototype.join = function(s) {
    var len    = this.length
    var result = ""
    for (var i=0;i<len;i++) {
      if (i>0 && i<len-1) result += s
      result += this[i]
    }
    return result
  }
}