module Register

  # GetByte moves a single byte into a register from memory.

  # indexes are 1 based (as for slots) , which means we sacrifice a byte of every word
  #        for our sanity

  class GetByte < Instruction

    # If you had a c array (of int8) and index offset
    # the instruction would do register = array[index]
    # The arguments are in the order that makes sense for the Instruction name
    # So GetSlot means the slot (array and index) moves to the register (last argument)
    def initialize source , array , index , register
      super(source)
      @array = array
      @index = index
      @register = register
      raise "index 0 " if index == 0
      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
      raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
      raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
    end
    attr_accessor :array , :index , :register

    def to_s
      "GetByte: #{array}[#{index}] -> #{register}"
    end

  end

  # Produce a GetByte instruction.
  # from and to are translated (from symbol to register if neccessary)
  # but index is left as is.
  def self.get_byte source , array , index , to
    from = resolve_to_register from
    to = resolve_to_register to
    GetByte.new( source , array , index , to)
  end
end