class Assembler(object):
WHITESPACE_CHARACTERS = ['\n', '\t', '\r', ' ']
COMMENT_MARKER = '//'
def __init__(self, filename):
self.filename = filename
self.next_output_line_num = 0
self.symbol_table = SymbolTable()
# TODO: it would be great if this could be defined globally instead of
# in the class init
self.command_type_to_code_generator = {
CommandType.A_COMMAND: self.build_a_command,
CommandType.C_COMMAND: CCommandBuilder.build_c_command,
}
def assemble(self):
with open(self.filename, 'r') as asm_file:
self.iter_file(asm_file, self.maybe_add_label_symbol)
self.iter_file(asm_file, self.generate_code_for_line)
def iter_file(self, asm_file, method):
asm_file.seek(0)
next_output_line_num = 0
for line in asm_file:
line = self.sanitize_line(line)
command_type = self.categorize_line(line)
if not command_type:
continue
method(line, command_type, next_output_line_num)
if self.should_increment_line_num(command_type):
next_output_line_num += 1
def categorize_line(self, line):
if not line:
return None
if line[0] == '@':
return CommandType.A_COMMAND
elif line[0] == '(':
return CommandType.LABEL
else:
return CommandType.C_COMMAND
def sanitize_line(self, line):
line = self.strip_comment(line)
line = self.strip_whitespace(line)
if line:
return line
def strip_comment(self, line):
comment_start_index = line.find(self.COMMENT_MARKER)
if comment_start_index != -1:
return line[:comment_start_index]
return line
def strip_whitespace(self, line):
for whitespace_character in self.WHITESPACE_CHARACTERS:
line = line.replace(whitespace_character, '')
return line
def should_increment_line_num(self, command_type):
return command_type in self.command_type_to_code_generator.keys()
def maybe_add_label_symbol(self, sanitized_line, command_type, line_num):
if command_type != CommandType.LABEL:
return
label_symbol = sanitized_line[1:-1]
if self.is_symbol(label_symbol):
self.symbol_table.add_label_symbol(label_symbol, line_num)
else:
raise Exception('Labels must be alphanumeric')
def maybe_add_variable_symbol(self, sanitized_line, line_num):
variable_symbol = self.extract_value_from_a_command(sanitized_line)
if self.is_symbol(variable_symbol):
self.symbol_table.maybe_add_variable_symbol(variable_symbol)
def extract_value_from_a_command(self, a_command):
return a_command[1:]
def is_symbol(self, string):
try:
int(string)
except ValueError:
return True
return False
def generate_code_for_line(self, line, command_type, line_num):
if command_type == CommandType.LABEL:
return
output_line = self.command_type_to_code_generator[command_type](line)
print output_line
def build_a_command(self, sanitized_line):
value = self.extract_value_from_a_command(sanitized_line)
if self.is_symbol(value):
address = self.symbol_table.get_or_add_variable_symbol(value)
else:
address = base10_to_binary(value)
return '0{}'.format(address.zfill(15))
