Class: GBRb::InstructionSet::Jump

Inherits:
Instruction show all
Defined in:
lib/gbrb/instruction_set/jump.rb

Instance Attribute Summary

Attributes inherited from Instruction

#i, #m, #t

Instance Method Summary collapse

Methods inherited from Instruction

#carry?, #immediate_count

Constructor Details

#initialize(condition, m = 2, t_high = 12, t_low = 8, immediates = 1) ⇒ Jump

Returns a new instance of Jump.



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# File 'lib/gbrb/instruction_set/jump.rb', line 5

def initialize condition, m=2, t_high=12, t_low=8, immediates=1
  super m, t_low, immediates
  @m_low = m
  @t_high = t_high
  @t_low = t_low
  @condition = condition.downcase.to_sym
end

Instance Method Details

#call(r, mem, offset = 0x00) ⇒ Object 



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# File 'lib/gbrb/instruction_set/jump.rb', line 13

def call r, mem, offset=0x00
  do_it = case @condition
          when :c
            r.carry_flag?
          when :none
            true
          when :nc
            not r.carry_flag?
          when :nz
            not r.zero_flag?
          when :z
            r.zero_flag?
          else
            false
          end

  if do_it
    @t = @t_high
    @m = @t_high / 4
    if @immediates == 0
      r.pc.store r.hl.read
    elsif @immediates == 1
      sign = (offset >> 7 == 1) ? :- : :+
      offset = ((offset ^ 0xff) + 1) & 0xff if sign == :-
      r.pc.store r.pc.read.public_send(sign, offset)
    else
      r.pc.store offset
    end
  else
    @t = @t_low
    @m = @m_low
  end
end