def restore_vm_symbols(symbol):
frame_minus()
primitive_ml.add_line('@' + symbol)
primitive_ml.add_line('M=D')
def write_if(location):
primitive_ml.read_stack_to('D')
primitive_ml.add_line('@' + location)
primitive_ml.add_line('D;JNE')
def read_symbol_to_stack(symbol):
primitive_ml.add_line('@' + symbol)
primitive_ml.write_c_command('D', 'M')
primitive_ml.write_to_stack('D')
def go_to_return_address():
primitive_ml.add_line('@RET')
primitive_ml.add_line('A=M')
primitive_ml.add_line('0;JMP')
def frame_descrese_to_d():
primitive_ml.add_line('@FRAME')
primitive_ml.add_line('M=M-1')
primitive_ml.add_line('A=M')
primitive_ml.write_c_command('D', 'M')
def write_call(name, var_count):
# push return-address (using label below)
global return_counter
return_label = 'return.' + str(return_counter)
primitive_ml.add_line('@' + return_label)
primitive_ml.write_c_command('D', 'A')
primitive_ml.write_to_stack('D')
# push lcl
read_symbol_to_stack('LCL')
read_symbol_to_stack('ARG')
read_symbol_to_stack('THIS')
read_symbol_to_stack('THAT')
# reposition arg
primitive_ml.add_line('@SP')
primitive_ml.write_c_command('D', 'M')
primitive_ml.add_line('@ARG')
primitive_ml.write_c_command('M', 'D')
primitive_ml.add_line('@5')
primitive_ml.write_c_command('D', 'A')
primitive_ml.add_line('@ARG')
primitive_ml.write_c_command('M', 'M-D')
primitive_ml.add_line('@' + str(var_count))
primitive_ml.write_c_command('D', 'A')
primitive_ml.add_line('@ARG')
primitive_ml.write_c_command('M', 'M-D')
# reposition lcl
primitive_ml.add_line('@SP')
primitive_ml.write_c_command('D', 'M')
primitive_ml.add_line('@LCL')
primitive_ml.write_c_command('M', 'D')
# goto function
primitive_ml.unconditional_jump(name)
# declare return label
primitive_ml.add_symbol_link(return_label)
return_counter += 1
return
def frame_minus():
primitive_ml.add_line('@FRAME')
primitive_ml.add_line('M=M-1')
primitive_ml.add_line('A=M')
primitive_ml.add_line('D=M')
def save_return_address():
primitive_ml.add_line('@5')
primitive_ml.add_line('D=D-A')
primitive_ml.add_line('A=D')
primitive_ml.add_line('D=M')
primitive_ml.add_line('@RET')
primitive_ml.add_line('M=D')
def frame():
primitive_ml.add_line('@LCL')
primitive_ml.write_c_command('D', 'M')
primitive_ml.add_line('@FRAME')
d_to_m()
primitive_ml.add_line('D=M')
def reposition_return_val():
primitive_ml.read_stack_to('D')
primitive_ml.add_line('@ARG')
primitive_ml.add_line('A=M')
primitive_ml.add_line('M=D')
def restore_sp_of_caller():
primitive_ml.add_line('@ARG')
primitive_ml.add_line('D=M')
primitive_ml.set_stack_pointer('D+1')