137 lines
3.1 KiB
Ruby
137 lines
3.1 KiB
Ruby
# frozen_string_literal: true
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require_relative 'array'
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class Packer
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# Format: ESDDDDDD EDDDDDDD EDD... Extended, Data, Sign
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def self.pack_int(num)
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# the first byte can fit 6 bits
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# because the first two bits are extended and sign
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# so if you have a number bigger than 63
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# it needs two bytes
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# which are also least significant byte first etc
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# so we do not support that YET
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#
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# the first too big number 64 is represented as those bits
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# 10000000 00000001
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# ^^^ ^ ^^ ^
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# ||\ / | \ /
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# || \ / not \ /
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# || \ extended
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# || \ /
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# || \ /
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# || \ /
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# || \/
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# || /\
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# || / \
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# || / \
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# || 0000001 000000
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# || |
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# || v
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# || 64
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# ||
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# |positive
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# extended
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sign = '0'
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if num.negative?
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sign = '1'
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num += 1
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end
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num = num.abs
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return pack_big_int(sign, num) if num > 63 || num < -63
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ext = '0'
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bits = ext + sign + num.to_s(2).rjust(6, '0')
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[bits.to_i(2)]
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end
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def self.pack_big_int(sign, num)
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num_bits = num.to_s(2)
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first = "1#{sign}#{num_bits[-6..]}"
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num_bits = num_bits[0..-7]
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bytes = []
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num_bits.chars.groups_of(7).each do |seven_bits|
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# mark all as extended
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bytes << "1#{seven_bits.join.rjust(7, '0')}"
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end
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# least significant first
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bytes = bytes.reverse
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# mark last byte as unextended
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bytes[-1][0] = '0'
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([first] + bytes).map { |b| b.to_i(2) }
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end
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def self.pack_str(str)
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str.chars.map(&:ord) + [0x00]
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end
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end
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class Unpacker
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def initialize(data)
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@data = data
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if data.instance_of?(String)
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@data = data.unpack('C*')
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elsif data.instance_of?(Array)
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@data = data
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else
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raise 'Error: Unpacker expects array of integers or byte string'
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end
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end
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def get_string
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return nil if @data.nil?
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str = ''
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@data.each_with_index do |byte, index|
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if byte.zero?
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@data = index == @data.length - 1 ? nil : @data[(index + 1)..]
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return str
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end
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str += byte.chr
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end
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# raise "get_string() failed to find null terminator"
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# return empty string in case of error
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''
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end
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def get_int
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return nil if @data.nil?
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# TODO: make this more performant
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# it should not read in ALL bytes
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# of the WHOLE packed data
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# it should be max 4 bytes
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# because bigger ints are not sent anyways
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bytes = @data.map { |byte| byte.to_s(2).rjust(8, '0') }
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first = bytes[0]
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sign = first[1]
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bits = []
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# extended
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if first[0] == '1'
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bits << first[2..]
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bytes = bytes[1..]
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consumed = 1
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bytes.each do |eigth_bits|
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bits << eigth_bits[1..]
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consumed += 1
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break if eigth_bits[0] == '0'
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end
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bits = bits.reverse
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@data = @data[consumed..]
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else # single byte
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bits = [first[2..]]
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@data = @data[1..]
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end
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num = bits.join.to_i(2)
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sign == '1' ? -(num + 1) : num
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end
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end
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u = Unpacker.new(['01000000'.to_i(2)])
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# expect -1
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p u.get_int
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