code: def __execute_sext(self, instr):
          
          op0_size = instr.operands[0].size
          op2_size = instr.operands[2].size
  
          op0_val = self.read_operand(instr.operands[0])
          op0_msb = extract_sign_bit(op0_val, op0_size)
  
          op2_mask = (2**op2_size-1) & ~(2**op0_size-1) if op0_msb == 1 else 0x0
  
          op2_val = op0_val | op2_mask
  
          self.write_operand(instr.operands[2], op2_val)
  
          return None
docs: Execute SEXT instruction.