def add(cpu, oper, mode):
"""
See :data:`~mach8.operations.ADC`.
"""
operand = _load_am(cpu, mode)
carry = 1 if cpu.c else 0
if cpu.d:
b1 = vm.bcd_inverse(cpu.a)
b2 = vm.bcd_inverse(operand)
bcd = b1 + b2 + carry
cpu.c = bcd > vm.DIGITS2
if bcd > vm.DIGITS2:
bcd -= vm.DIGITS2 + 1
result = vm.bcd_forward(bcd) & vm.BITS8
else:
value = cpu.a + operand + carry
cpu.c = value > vm.BITS8
result = value & vm.BITS8
signed = vm.twos_inverse(cpu.a) + vm.twos_inverse(operand)
cpu.v = signed > vm.SBYTE_MAX or signed < vm.SBYTE_MIN
_flags(cpu, result)
cpu.a = result
def sub(cpu, oper, mode):
"""
See :data:`~mach8.operations.SBC`,
"""
operand = _load_am(cpu, mode)
carry = 0 if cpu.c else 1
if cpu.d:
b1 = vm.bcd_inverse(cpu.a)
b2 = vm.bcd_inverse(operand)
value = b1 - b2 - carry
cpu.c = not value < 0
if value < 0:
value += 100
result = vm.bcd_forward(value) & vm.BITS8
else:
value = cpu.a - operand - carry
cpu.c = not value < 0
result = value & vm.BITS8
signed = vm.twos_inverse(cpu.a) - vm.twos_inverse(operand)
cpu.v = signed > vm.SBYTE_MAX or signed < vm.SBYTE_MIN
_flags(cpu, result)
cpu.a = result
def test_bcd_inverse(self):
self.assertEquals(42, vm.bcd_inverse(0x42))