Method: CRC::Calculator#unshiftbytes_by_bitbybit

Defined in:
lib/crc/_shift.rb

#unshiftbytes_by_bitbybit(byteset, state) ⇒ Object

call-seq:

unshiftbytes_by_bitbybit(byteset, state)

byteset を与えることで state となるような内部状態を逆算します。



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# File 'lib/crc/_shift.rb', line 107

def unshiftbytes_by_bitbybit(byteset, state)
  if reflect_input?
    poly = (CRC.bitreflect(polynomial, bitsize) << 1) | 1
    head = bitsize
    byteset.reverse_each_byte do |b|
      7.downto(0) do |i|
        state <<= 1
        state ^= poly unless state[head] == 0
        state ^= b[i]
      end
    end

    state
  else
    Aux.slide_to_head(bitsize, state, polynomial, bitmask) do |s, poly, csh, head, carries|
      headbit = 1 << head
      lowoff = (head + 1) - bitsize
      poly = (poly >> 1) | headbit
      byteset.reverse_each_byte do |b|
        8.times do |i|
          tmp = s[lowoff]
          s >>= 1
          s ^= poly unless tmp == 0
          s ^= b[i] << head
        end
      end

      s
    end
  end
end