decoder.py

import dis

from instruction import Instruction


class Decoder:
 """
 Class to decode raw bytes into instruction.
 """

 def __init__(self, insBytes):
 self.insBytes = insBytes

 def decode_at(self, offset):
 assert offset < len(self.insBytes)

 opcode = self.insBytes[offset]

 if opcode == dis.opmap['EXTENDED_ARG']:
 raise Exception('EXTENDED_ARG not yet implemented')

 # Invalid instruction
 if opcode not in dis.opmap.values():
 return Instruction(-1, None, 1)

 if opcode < dis.HAVE_ARGUMENT:
 return Instruction(opcode, None, 1)

 if opcode >= dis.HAVE_ARGUMENT:
 arg = (self.insBytes[offset + 2] << 8) | self.insBytes[offset + 1]
 return Instruction(opcode, arg, 3)