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