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 Ruby generated by Kaitai Struct depends on the Ruby runtime library. You have to install it before you can parse data.
The Ruby runtime library can be installed from RubyGems:
gem install kaitai-structParse a local file and get structure in memory:
data = VlqBase128Be.from_file("path/to/local/file.bin")
Or parse structure from a string of bytes:
bytes = "\x00\x01\x02..."
data = VlqBase128Be.new(Kaitai::Struct::Stream.new(bytes))
After that, one can get various attributes from the structure by invoking getter methods 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
require 'kaitai/struct/struct'
unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.9')
raise "Incompatible Kaitai Struct Ruby API: 0.9 or later is required, but you have #{Kaitai::Struct::VERSION}"
end
##
# 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.
class VlqBase128Be < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@groups = []
i = 0
begin
_ = Group.new(@_io, self, @_root)
@groups << _
i += 1
end until !(_.has_next)
self
end
##
# One byte group, clearly divided into 7-bit "value" chunk and 1-bit "continuation" flag.
class Group < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@has_next = @_io.read_bits_int_be(1) != 0
@value = @_io.read_bits_int_be(7)
self
end
##
# If true, then we have more bytes to read
attr_reader :has_next
##
# The 7-bit (base128) numeric value chunk of this group
attr_reader :value
end
def last
return @last unless @last.nil?
@last = (groups.length - 1)
@last
end
##
# Resulting value as normal integer
def value
return @value unless @value.nil?
@value = (((((((groups[last].value + (last >= 1 ? (groups[(last - 1)].value << 7) : 0)) + (last >= 2 ? (groups[(last - 2)].value << 14) : 0)) + (last >= 3 ? (groups[(last - 3)].value << 21) : 0)) + (last >= 4 ? (groups[(last - 4)].value << 28) : 0)) + (last >= 5 ? (groups[(last - 5)].value << 35) : 0)) + (last >= 6 ? (groups[(last - 6)].value << 42) : 0)) + (last >= 7 ? (groups[(last - 7)].value << 49) : 0))
@value
end
attr_reader :groups
end