sm.py

#
# Opcode values.
#
HALT  = 0
LOAD  = 1
STORE = 2
ADDC  = 3
MVAC  = 4
JEQ   = 5
JLT   = 6
JMP   = 7
ADD   = 8
SUB   = 9
DEC   = 10
LA    = 11
LIA   = 12
SIA   = 13
MVAA  = 14


#
# Opcode name map.
#
opcode_name = [
         'HALT',
         'LOAD',
         'STORE',
         'ADDC',
         'MVAC',
         'JEQ',
         'JLT',
         'JMP',
         'ADD',
         'SUB',
         'DEC',
         'LA',
         'LIA',
         'SIA',
         'MVAA',
         ]


class Label:
    def __init__(self, addr):
        self.addr = addr

    def resolve(self, prog):
        return self.addr

    def describe(self):
        return str(self.addr)


class Instruction:
    """
    An instruction.
    """
    def __init__(self, opcode, addr=None):
        self.opcode = opcode
        self.addr = addr

    def encode(self, prog):
        code = self.opcode << 12
        if self.addr:
            code |= self.addr.resolve(prog)
        return code

    def describe(self):
        s = opcode_name[self.opcode]
        if self.addr:
            s += '\t' + self.addr.describe()
        return s


class Data:
    def __init__(self, name, val, offset):
        self.name = name
        self.val = val
        self.offset = offset

    def resolve(self, prog):
        return self.offset + prog.data_offset()

    def describe(self):
        return self.name


class Program:
    def __init__(self):
        self.instructions = []
        self.data_section = []

    def label(self):
        return Label(len(self.instructions))

    def add_instruction(self, instruction):
        lbl = self.label()
        self.instructions.append(instruction)
        return lbl

    def add_instructions(self, *args):
        for arg in args:
            self.add_instruction(Instruction(*arg))

    def add_data(self, name, val):
        item = Data(name, val, len(self.data_section))
        self.data_section.append(item)
        return item

    def data_offset(self):
        return len(self.instructions)

    def output(self):
        for instruction in self.instructions:
            print('0x{encoding:04x}\t# {description}'.format(
                encoding=instruction.encode(self),
                description=instruction.describe(),
                ))
        if len(self.data_section) == 0:
            return
        print('#')
        print('# Data Section.')
        print('#')
        for data in self.data_section:
            print('0x{val:04x}\t# {name}'.format(
                val=data.val,
                name=data.name,
                ))


def main():
    p = Program()
    N = p.add_data('N', 6)
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    loopstart = p.label()
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(LOAD, N))
    p.add_instruction(Instruction(JMP, loopstart))
    p.add_instruction(Instruction(HALT))
    p.output()


if __name__ == '__main__':
    main()