def assemble(self):
#
# first pass - build the symbol table for labels
#
parser = Parser(self.source_filename)
symbol_table = SymbolTable()
# the current instruction
instruction = 0
# parse each command
while parser.hasMoreCommands():
# advance to the next command
parser.advance()
# parse the command type and look for symbols
command_type = parser.commandType()
if command_type == "L":
# look for an instruction label symbol
symbol = parser.symbol()
if symbol not in symbol_table:
symbol_table.addEntry(symbol, instruction)
else:
# increment the instruction count if this was not a label
if command_type != "L":
instruction += 1
#
# second pass - build the symbol table for variables
#
parser = Parser(self.source_filename)
# the memory location for the next variable
variable_address = 16
# parse each command
while parser.hasMoreCommands():
# advance to the next command
parser.advance()
# parse the command type and look for symbols
command_type = parser.commandType()
if command_type == "A":
# look for a variable value symbol
symbol = parser.symbol()
if symbol[0] not in map(str, range(0, 10)):
# the symbol is not a number; that is, it is actually a symbol
if symbol not in symbol_table:
symbol_table.addEntry(symbol, variable_address)
variable_address += 1
#
# third pass - generate assembly
#
parser = Parser(self.source_filename)
code = Code()
# parse all commands
while parser.hasMoreCommands():
# advance to the next command
parser.advance()
command_type = parser.commandType()
if command_type == "A":
# a command
symbol = parser.symbol()
if symbol in symbol_table:
symbol = symbol_table.getAddress(symbol)
symbol_binary = code.decimalToBinary(symbol)
self.destination_file.write("0" + symbol_binary + "\n")
elif command_type == "C":
# c command
comp = code.comp(parser.comp())
dest = code.dest(parser.dest())
jump = code.jump(parser.jump())
self.destination_file.write("111" + comp + dest + jump + "\n")
elif command_type == "L":
# label - do nothing in this stage
pass
else:
# unknown command
raise Exception("ERROR: Unknown command type encountered")
# close the output file
self.destination_file.close()
