A variable-length unsigned integer using base128 encoding. 1-byte groups consist of 1-bit flag of continuation and 7-bit value chunk, and are ordered "most significant group first", i.e. in "big-endian" manner.
This particular encoding is specified and used in:
More information on this encoding is available at https://en.wikipedia.org/wiki/Variable-length_quantity
This particular implementation supports serialized values to up 8 bytes long.
This page hosts a formal specification of Variable length quantity, unsigned integer, base128, big-endian using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for JavaScript generated by Kaitai Struct depends on the JavaScript runtime library. You have to install it before you can parse data.
The JavaScript runtime library is available at npm:
npm install kaitai-structSee the usage examples in the JavaScript notes.
Parse structure from an ArrayBuffer:
var arrayBuffer = ...;
var data = new VlqBase128Be(new KaitaiStream(arrayBuffer));
After that, one can get various attributes from the structure by accessing fields or properties like:
data.value // => Resulting value as normal integer
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
(function (root, factory) {
if (typeof define === 'function' && define.amd) {
define(['kaitai-struct/KaitaiStream'], factory);
} else if (typeof module === 'object' && module.exports) {
module.exports = factory(require('kaitai-struct/KaitaiStream'));
} else {
root.VlqBase128Be = factory(root.KaitaiStream);
}
}(typeof self !== 'undefined' ? self : this, function (KaitaiStream) {
/**
* A variable-length unsigned integer using base128 encoding. 1-byte groups
* consist of 1-bit flag of continuation and 7-bit value chunk, and are ordered
* "most significant group first", i.e. in "big-endian" manner.
*
* This particular encoding is specified and used in:
*
* * Standard MIDI file format
* * ASN.1 BER encoding
* * RAR 5.0 file format
*
* More information on this encoding is available at
* <https://en.wikipedia.org/wiki/Variable-length_quantity>
*
* This particular implementation supports serialized values to up 8 bytes long.
*/
var VlqBase128Be = (function() {
function VlqBase128Be(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
VlqBase128Be.prototype._read = function() {
this.groups = [];
var i = 0;
do {
var _ = new Group(this._io, this, this._root);
this.groups.push(_);
i++;
} while (!(!(_.hasNext)));
}
/**
* One byte group, clearly divided into 7-bit "value" chunk and 1-bit "continuation" flag.
*/
var Group = VlqBase128Be.Group = (function() {
function Group(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
Group.prototype._read = function() {
this.hasNext = this._io.readBitsIntBe(1) != 0;
this.value = this._io.readBitsIntBe(7);
}
/**
* If true, then we have more bytes to read
*/
/**
* The 7-bit (base128) numeric value chunk of this group
*/
return Group;
})();
Object.defineProperty(VlqBase128Be.prototype, 'last', {
get: function() {
if (this._m_last !== undefined)
return this._m_last;
this._m_last = (this.groups.length - 1);
return this._m_last;
}
});
/**
* Resulting value as normal integer
*/
Object.defineProperty(VlqBase128Be.prototype, 'value', {
get: function() {
if (this._m_value !== undefined)
return this._m_value;
this._m_value = (((((((this.groups[this.last].value + (this.last >= 1 ? (this.groups[(this.last - 1)].value << 7) : 0)) + (this.last >= 2 ? (this.groups[(this.last - 2)].value << 14) : 0)) + (this.last >= 3 ? (this.groups[(this.last - 3)].value << 21) : 0)) + (this.last >= 4 ? (this.groups[(this.last - 4)].value << 28) : 0)) + (this.last >= 5 ? (this.groups[(this.last - 5)].value << 35) : 0)) + (this.last >= 6 ? (this.groups[(this.last - 6)].value << 42) : 0)) + (this.last >= 7 ? (this.groups[(this.last - 7)].value << 49) : 0));
return this._m_value;
}
});
return VlqBase128Be;
})();
return VlqBase128Be;
}));