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d54c8f8 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 | 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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