binary_work_shower/register.py

class Register:
    registers = []

    def __init__(self, n_bits, name=None):
        self.n_bits = n_bits
        if name is None:
            self.name = "r{}".format(len(Register.registers))
        else:
            self.name = name
        self.value = 0
        Register.registers.append(self)

    def truncate_val(self, value, bits=None):
        if bits is None:
            bits = self.n_bits
        return value & ((1 << bits) - 1)

    def truncate(self):
        self.value = self.truncate_val(self.value)

    def set(self, value):
        if value < 0:
            self.value = self.truncate_val(abs(value), self.n_bits - 1)
            self.negate()
        else:
            self.value = value
            self.truncate()

    def get(self):
        return self.value

    def get_signed(self):
        if self.value & (1 << (self.n_bits - 1)) == 0:
            return self.value
        else:
            return self.value - (1 << self.n_bits)

    def complement(self):
        self.value = self.value ^ ((1 << self.n_bits) - 1)

    def negate(self):
        self.complement()
        self.value += 1

    def __str__(self):
        return "{:08b}".format(self.value)

    def __repr__(self):
        return "{} ({})".format(self, self.n_bits)


class Accumulator(Register):
    negative_flag = False
    zero_flag = False
    carry_flag = False
    parity_flag = False

    def set_flags(self):
        "Set accumulator flags after an arithmetic operation"
        self.negative_flag = False
        self.zero_flag = False

        if self.get_signed() < 0:
            self.negative_flag = True
        if self.get() == 0:
            self.zero_flag = True
        v = self.get()
        self.parity_flag = True
        while v > 0:
            if (v & 1) == 1:
                self.parity_flag = not self.parity_flag
            v >>= 1

    def add(self, register: Register):
        self.value += register.value
        if self.value.bit_length() > self.n_bits:
            self.carry_flag = True
            self.truncate()
        self.set_flags()

    def sub(self, register: Register):
        self.negate()
        self.add(register)
        self.negate()
        self.set_flags()

    def shift_right(self, through_carry=True):
        was_one = (self.get() & 1) == 1
        if through_carry:
            add_bit = self.carry_flag
        else:
            add_bit = was_one
        if add_bit:
            self.value |= 1 << (self.n_bits)
        self.value >>= 1
        self.carry_flag = was_one
        self.set_flags()

    def shift_left(self, through_carry=True):
        was_one = (self.get() & (1 << (self.n_bits - 1))) != 0
        if through_carry:
            add_bit = self.carry_flag
        else:
            add_bit = was_one
        self.value <<= 1
        if add_bit:
            self.value |= 1
        self.carry_flag = was_one
        self.set_flags()