147 lines
3.2 KiB
Ruby
147 lines
3.2 KiB
Ruby
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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# || \ / \ /
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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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# || / \
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# || 00000001 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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if num > 63 || num < -63
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return self.pack_big_int(sign, num)
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end
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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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def initialize(data)
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@data = data
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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 == 0x00
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if index == @data.length - 1
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@data = nil
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else
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@data = @data[(index + 1)..]
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end
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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.chars.groups_of(8)
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first = bytes[0]
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other = bytes[1..]
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sign = first[1] == '1' ? -1 : 1
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bits = ''
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# extended
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if first[0] == '1'
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bytes.each do |eigth_bits|
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end
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else # single byte
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bits = first[2..].join('')
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end
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bits.to_i(2) * sign
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end
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end
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def todo_make_this_rspec_test
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# single byte int
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p Packer.pack_int(1) == [1]
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p Packer.pack_int(3) == [3]
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p Packer.pack_int(16) == [16]
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p Packer.pack_int(63) == [63]
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# negative single byte
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p Packer.pack_int(-1) == [64]
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p Packer.pack_int(-2) == [65]
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# multi byte int
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p Packer.pack_int(64) == [128, 1]
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p Packer.pack_int(99999999999999999) == [191, 131, 255, 147, 246, 194, 215, 232, 88]
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# string
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p Packer.pack_str("A") == [65, 0]
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end
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def todo_also_rspec_unpacker
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p = Packer.new([0x41, 0x41, 0x00, 0x42, 0x42, 0x00])
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p p.get_string() == "AA"
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p p.get_string() == "BB"
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p p.get_string() == nil
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end
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todo_also_rspec_unpacker
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