Class: Packer

Inherits:
Object
  • Object
show all
Defined in:
lib/packer.rb

Class Method Summary collapse

Class Method Details

.pack_big_int(sign, num) ⇒ Object 



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# File 'lib/packer.rb', line 52

def self.pack_big_int(sign, num)
  num_bits = num.to_s(2)
  first = "1#{sign}#{num_bits[-6..]}"

  num_bits = num_bits[0..-7]
  bytes = []
  num_bits.chars.groups_of(7).each do |seven_bits|
    # mark all as extended
    bytes << "1#{seven_bits.join.rjust(7, '0')}"
  end
  # least significant first
  bytes = bytes.reverse
  # mark last byte as unextended
  bytes[-1][0] = '0'
  ([first] + bytes).map { |b| b.to_i(2) }
end

.pack_int(num) ⇒ Object

Format: ESDDDDDD EDDDDDDD EDD… Extended, Data, Sign



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# File 'lib/packer.rb', line 11

def self.pack_int(num)
  # the first byte can fit 6 bits
  # because the first two bits are extended and sign
  # so if you have a number bigger than 63
  # it needs two bytes
  # which are also least significant byte first etc
  # so we do not support that YET
  #
  # the first too big number 64 is represented as those bits
  # 10000000 00000001
  # ^^^    ^ ^^    ^
  # ||\   /  | \   /
  # || \ / not  \ /
  # ||  \ extended
  # ||   \      /
  # ||    \    /
  # ||     \  /
  # ||      \/
  # ||      /\
  # ||     /  \
  # ||    /    \
  # || 0000001 000000
  # ||       |
  # ||       v
  # ||       64
  # ||
  # |positive
  # extended
  sign = '0'
  if num.negative?
    sign = '1'
    num += 1
  end
  num = num.abs
  return pack_big_int(sign, num) if num > 63 || num < -63

  ext = '0'
  bits = ext + sign + num.to_s(2).rjust(6, '0')
  [bits.to_i(2)]
end

.pack_str(str) ⇒ Object 



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# File 'lib/packer.rb', line 69

def self.pack_str(str)
  str.chars.map(&:ord) + [0x00]
end