96 lines
2.2 KiB
JavaScript
96 lines
2.2 KiB
JavaScript
var pager = require('memory-pager')
|
|
|
|
module.exports = Bitfield
|
|
|
|
function Bitfield (opts) {
|
|
if (!(this instanceof Bitfield)) return new Bitfield(opts)
|
|
if (!opts) opts = {}
|
|
if (Buffer.isBuffer(opts)) opts = {buffer: opts}
|
|
|
|
this.pageOffset = opts.pageOffset || 0
|
|
this.pageSize = opts.pageSize || 1024
|
|
this.pages = opts.pages || pager(this.pageSize)
|
|
|
|
this.byteLength = this.pages.length * this.pageSize
|
|
this.length = 8 * this.byteLength
|
|
|
|
if (!powerOfTwo(this.pageSize)) throw new Error('The page size should be a power of two')
|
|
|
|
this._trackUpdates = !!opts.trackUpdates
|
|
this._pageMask = this.pageSize - 1
|
|
|
|
if (opts.buffer) {
|
|
for (var i = 0; i < opts.buffer.length; i += this.pageSize) {
|
|
this.pages.set(i / this.pageSize, opts.buffer.slice(i, i + this.pageSize))
|
|
}
|
|
this.byteLength = opts.buffer.length
|
|
this.length = 8 * this.byteLength
|
|
}
|
|
}
|
|
|
|
Bitfield.prototype.get = function (i) {
|
|
var o = i & 7
|
|
var j = (i - o) / 8
|
|
|
|
return !!(this.getByte(j) & (128 >> o))
|
|
}
|
|
|
|
Bitfield.prototype.getByte = function (i) {
|
|
var o = i & this._pageMask
|
|
var j = (i - o) / this.pageSize
|
|
var page = this.pages.get(j, true)
|
|
|
|
return page ? page.buffer[o + this.pageOffset] : 0
|
|
}
|
|
|
|
Bitfield.prototype.set = function (i, v) {
|
|
var o = i & 7
|
|
var j = (i - o) / 8
|
|
var b = this.getByte(j)
|
|
|
|
return this.setByte(j, v ? b | (128 >> o) : b & (255 ^ (128 >> o)))
|
|
}
|
|
|
|
Bitfield.prototype.toBuffer = function () {
|
|
var all = alloc(this.pages.length * this.pageSize)
|
|
|
|
for (var i = 0; i < this.pages.length; i++) {
|
|
var next = this.pages.get(i, true)
|
|
var allOffset = i * this.pageSize
|
|
if (next) next.buffer.copy(all, allOffset, this.pageOffset, this.pageOffset + this.pageSize)
|
|
}
|
|
|
|
return all
|
|
}
|
|
|
|
Bitfield.prototype.setByte = function (i, b) {
|
|
var o = i & this._pageMask
|
|
var j = (i - o) / this.pageSize
|
|
var page = this.pages.get(j, false)
|
|
|
|
o += this.pageOffset
|
|
|
|
if (page.buffer[o] === b) return false
|
|
page.buffer[o] = b
|
|
|
|
if (i >= this.byteLength) {
|
|
this.byteLength = i + 1
|
|
this.length = this.byteLength * 8
|
|
}
|
|
|
|
if (this._trackUpdates) this.pages.updated(page)
|
|
|
|
return true
|
|
}
|
|
|
|
function alloc (n) {
|
|
if (Buffer.alloc) return Buffer.alloc(n)
|
|
var b = new Buffer(n)
|
|
b.fill(0)
|
|
return b
|
|
}
|
|
|
|
function powerOfTwo (x) {
|
|
return !(x & (x - 1))
|
|
}
|