Class: GBRb::InstructionSet::Dec

Inherits:
Instruction show all
Defined in:
lib/gbrb/instruction_set/arithmetic.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(register, m = 1, t = 4, flags = true, indirect = false) ⇒ Dec

Returns a new instance of Dec.



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# File 'lib/gbrb/instruction_set/arithmetic.rb', line 202

def initialize register, m=1, t=4, flags=true, indirect=false
  super m, t

  @register = register
  @flags = flags
  @op = :-
  @indirect = indirect
end

Instance Method Details

#call(r, mem) ⇒ Object 



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# File 'lib/gbrb/instruction_set/arithmetic.rb', line 211

def call r, mem
  reg = r.public_send(@register.to_sym)
  tmp = reg.read
  if @indirect
    v = mem.read_byte(tmp)
    mem.write_byte(tmp, v - 1)
    tmp = v
    half_mask = r.a.half_mask
  else
    reg.store tmp - 0x01
    half_mask = reg.half_mask
  end
  if @flags
    r.set_add_sub_flag
    if (tmp - 0x01) == 0x00
      r.set_zero_flag
    else
      r.clear_zero_flag
    end
    if carry? tmp, 0x01, half_mask
      r.set_half_carry_flag
    else
      r.clear_half_carry_flag
    end
  end
end