module.exports = Pager function Pager (pageSize, opts) { if (!(this instanceof Pager)) return new Pager(pageSize, opts) this.length = 0 this.updates = [] this.pages = new Array(16) this.pageSize = pageSize || 1024 this.deduplicate = opts ? opts.deduplicate : null this.zeros = this.deduplicate ? alloc(this.deduplicate.length) : null } Pager.prototype.updated = function (page) { while (this.deduplicate && page.buffer[page.deduplicate] === this.deduplicate[page.deduplicate]) { page.deduplicate++ if (page.deduplicate === this.deduplicate.length) { page.deduplicate = 0 if (page.buffer.equals && page.buffer.equals(this.deduplicate)) page.buffer = this.deduplicate break } } if (page.updated || !this.updates) return page.updated = true this.updates.push(page) } Pager.prototype.lastUpdate = function () { if (!this.updates || !this.updates.length) return null var page = this.updates.pop() page.updated = false return page } Pager.prototype.get = function (i, noAllocate) { if (i >= this.pages.length) { if (noAllocate) return this.pages = grow(this.pages, i, this.length) } var page = this.pages[i] if (!page && !noAllocate) { page = this.pages[i] = new Page(i, alloc(this.pageSize)) if (i >= this.length) this.length = i + 1 } if (page && page.buffer === this.deduplicate && this.deduplicate && !noAllocate) { page.buffer = copy(page.buffer) page.deduplicate = 0 } return page } Pager.prototype.set = function (i, buf) { if (i >= this.pages.length) this.pages = grow(this.pages, i, this.length) if (i >= this.length) this.length = i + 1 if (!buf || (this.zeros && buf.equals && buf.equals(this.zeros))) { this.pages[i] = undefined return } if (this.deduplicate && buf.equals && buf.equals(this.deduplicate)) { buf = this.deduplicate } var page = this.pages[i] var b = truncate(buf, this.pageSize) if (page) page.buffer = b else this.pages[i] = new Page(i, b) } Pager.prototype.toBuffer = function () { var list = new Array(this.length) var empty = alloc(this.pageSize) for (var i = 0; i < list.length; i++) { list[i] = this.pages[i] ? this.pages[i].buffer : empty } return Buffer.concat(list) } function grow (list, index, len) { var nlen = list.length * 2 while (nlen <= index) nlen *= 2 var twice = new Array(nlen) for (var i = 0; i < len; i++) twice[i] = list[i] return twice } function truncate (buf, len) { if (buf.length === len) return buf if (buf.length > len) return buf.slice(0, len) var cpy = alloc(len) buf.copy(cpy) return cpy } function alloc (size) { if (Buffer.alloc) return Buffer.alloc(size) var buf = new Buffer(size) buf.fill(0) return buf } function copy (buf) { var cpy = Buffer.allocUnsafe ? Buffer.allocUnsafe(buf.length) : new Buffer(buf.length) buf.copy(cpy) return cpy } function Page (i, buf) { this.offset = i * buf.length this.buffer = buf this.updated = false this.deduplicate = 0 }