Class: VCDIFF::VCDIFFInt

Inherits:
BinData::BasePrimitive
  • Object
show all
Defined in:
lib/vcdiff/integer.rb

Overview

As described in RFC 3284 (tools.ietf.org/html/rfc3284) unsigned integers are treated as a number in base 128. Each digit in this representation is encoded in the lower 7 bits of a byte. Runs of bytes b_1, b_2, b_3, …, b_n for one integer have the most significant bit set to 1 for each b_i, i = 1, …, n-1, and set to 0 for b_n.

So 123456789 encodes to four 7-bit digits with values 58, 111, 26, 21:

+-------------------------------------------+
| 10111010 | 11101111 | 10011010 | 00010101 |
+-------------------------------------------+
  MSB+58     MSB+111    MSB+26     0+21

Instance Method Summary collapse

Instance Method Details

#read_and_return_value(io) ⇒ Object 



40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
 
# File 'lib/vcdiff/integer.rb', line 40

def read_and_return_value(io)
  byte_values = []
  value = 0

  loop do
    b = next_byte(io)
    last_byte = (b[7] == 0)

    byte_values << (b & 0b01111111)

    break if last_byte
  end

  byte_values.reverse.each_with_index do |e, i|
    # add byte * 128**i, since e is considered to be
    # a number in base 128
    value += e * (1 << (7 * i))
  end

  value
end

#sensible_default ⇒ Object 



62
63
64
 
# File 'lib/vcdiff/integer.rb', line 62

def sensible_default
  0
end

#to_i ⇒ Object

Gives the VCDIFF integer as a regular Ruby Integer



75
76
77
 
# File 'lib/vcdiff/integer.rb', line 75

def to_i
  snapshot
end

#value_to_binary_string(value) ⇒ Object 



20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
 
# File 'lib/vcdiff/integer.rb', line 20

def value_to_binary_string(value)
  bytes = []

  loop do
    # get the value of the lowest 7 bits
    next_value = value & 0b01111111

    value >>= 7

    # on every byte except the first one, flip the 8th bit on
    next_value = 0b10000000 | next_value unless bytes.empty?

    bytes.unshift(next_value)

    break if value == 0
  end

  bytes.pack("C*")
end

#value_to_zero_one_string ⇒ Object

Converts a Ruby Integer into a string where each character is either 0 or 1, fully representing the bytes in the array.

TODO: a non-awful method name and non-awful implementation



70
71
72
 
# File 'lib/vcdiff/integer.rb', line 70

def value_to_zero_one_string
  to_binary_s.unpack("C*").map { |e| e.to_s(2).rjust(8, "0") }.join("")
end