module LEB128

Includes a set of functions to encode and decode the LEB128 integer compression type.

Public Class Methods

decode_signed(io, index = 0) click to toggle source

Decode signed LEB128-compressed data into an integer.

@param io [StringIO] @param index [Integer] @return [Integer]

@example

sio = StringIO.new
sio.putc(0xc1)
sio.putc(0x57)
LEB128.decode_signed(sio) #=> -5183

# File lib/leb128.rb, line 90
def self.decode_signed(io, index = 0)
  io.pos = index
  raise(EOFError) if io.eof?
  value = 0
  offset = 0
  loop do
    byte = io.read(1).unpack('C')[0]
    value |= (byte & 0x7F) << offset
    offset += 7
    if byte & 0x80 == 0
      value |= -(1 << offset) unless byte & 0x40 == 0
      break
    end
  end
  value
end
decode_unsigned(io, index = 0) click to toggle source

Decode unsigned LEB128-compressed data into an integer.

@param io [StringIO] @param index [Integer] @return [Integer]

@example

sio = StringIO.new
sio.putc(0xc1)
sio.putc(0x57)
LEB128.decode_unsigned(sio) #=> 11201

# File lib/leb128.rb, line 64
def self.decode_unsigned(io, index = 0)
  io.pos = index
  raise(EOFError) if io.eof?
  value = 0
  offset = 0
  loop do
    byte = io.read(1).unpack('C')[0]
    value |= (byte & 0x7F) << offset
    break if byte & 0x80 == 0
    offset += 7
  end
  value
end
encode_signed(value) click to toggle source

Encode a signed integer into LEB128-compressed data.

@param value [Integer] @return [StringIO]

@example

LEB128.encode_signed(-0x143f) #=> #<StringIO:0x00000000000000>

# File lib/leb128.rb, line 38
def self.encode_signed(value)
  io = StringIO.new
  loop do
    byte = value & 0x7F
    value >>= 7
    byte |= 0x80 unless (value == 0 && byte & 0x40 == 0) ||
                        (value == -1 && byte & 0x40 != 0)
    io.putc(byte)
    break if byte & 0x80 == 0
  end
  io.pos = 0
  io
end
encode_unsigned(value) click to toggle source

Encode an unsigned integer into LEB128-compressed data.

@param value [Integer] @return [StringIO]

@example

LEB128.encode_unsigned(0x2bc1) #=> #<StringIO:0x00000000000000>

# File lib/leb128.rb, line 13
def self.encode_unsigned(value)
  if value < 0
    raise(ArgumentError,
          'Cannot encode a negative integer to an unsigned LEB128')
  end
  io = StringIO.new
  loop do
    byte = value & 0x7F
    value >>= 7
    byte |= 0x80 if value != 0
    io.putc(byte)
    break if value == 0
  end
  io.pos = 0
  io
end