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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))
}