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module.exports = Pager
function Pager (pageSize, opts) {
if (!(this instanceof Pager)) return new Pager(pageSize, opts)
this.length = 0
this.updates = []
this.path = new Uint16Array(4)
this.pages = new Array(32768)
this.maxPages = this.pages.length
this.level = 0
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._array = function (i, noAllocate) {
if (i >= this.maxPages) {
if (noAllocate) return
grow(this, i)
}
factor(i, this.path)
var arr = this.pages
for (var j = this.level; j > 0; j--) {
var p = this.path[j]
var next = arr[p]
if (!next) {
if (noAllocate) return
next = arr[p] = new Array(32768)
}
arr = next
}
return arr
}
Pager.prototype.get = function (i, noAllocate) {
var arr = this._array(i, noAllocate)
var first = this.path[0]
var page = arr && arr[first]
if (!page && !noAllocate) {
page = arr[first] = 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) {
var arr = this._array(i, false)
var first = this.path[0]
if (i >= this.length) this.length = i + 1
if (!buf || (this.zeros && buf.equals && buf.equals(this.zeros))) {
arr[first] = undefined
return
}
if (this.deduplicate && buf.equals && buf.equals(this.deduplicate)) {
buf = this.deduplicate
}
var page = arr[first]
var b = truncate(buf, this.pageSize)
if (page) page.buffer = b
else arr[first] = new Page(i, b)
}
Pager.prototype.toBuffer = function () {
var list = new Array(this.length)
var empty = alloc(this.pageSize)
var ptr = 0
while (ptr < list.length) {
var arr = this._array(ptr, true)
for (var i = 0; i < 32768 && ptr < list.length; i++) {
list[ptr++] = (arr && arr[i]) ? arr[i].buffer : empty
}
}
return Buffer.concat(list)
}
function grow (pager, index) {
while (pager.maxPages < index) {
var old = pager.pages
pager.pages = new Array(32768)
pager.pages[0] = old
pager.level++
pager.maxPages *= 32768
}
}
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
}
function factor (n, out) {
n = (n - (out[0] = (n & 32767))) / 32768
n = (n - (out[1] = (n & 32767))) / 32768
out[3] = ((n - (out[2] = (n & 32767))) / 32768) & 32767
}
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