Re:GOTOphobia Considered Harmful (In C)
by ivalm on Sunday February 26, 2023 @03:11PM
(#34948884)
Do you know of a good example you could link?
[ Parent
| on HN ]
Something like this is the best I could find: https://craftofcoding.files.wordpress.com/2018/01/fortran_go... – the last page has a full listing with arrows to show the jumps.
I grew up with MSX-BASIC: https://github.com/plattysoft/Modern-MSX-BASIC-Game-Dev/blob... – GOSUB jumps to a specific line number (RETURN returns from where it jumped). Even a fairly simple and clean example like this can be rather difficult to follow.
The first part of Guy Steele's talk on Fortress: https://www.infoq.com/presentations/Thinking-Parallel-Progra...
I dug around a little and found an example [1] on a reddit thread looking for examples of spaghetti code. Most of the examples on the thread were just badly written code. Irreducible spaghetti code tends to be complex state machines that cannot be rendered well in a flat format. People like to flatten those out with a trampoline pattern[2], but that can hinder performance.
Malicious spaghetti involves transformations such as
for (x = 0; x < 10; x++) {
for (y = 0; y < 20; y++) {
printf("%d %d\n", x, y);
}
}
|
| DRY
v
x = 0;
loop_x_head:
condition_val = x;
condition_stop = 10;
condition_var = 'x';
goto check_condition;
loop_x_body:
y = 0;
loop_y_head:
condition_val = y;
condition_stop = 20;
condition_var = 'y';
goto check_condition;
loop_y_body:
printf("%d %d\n", x, y);
increment_val = y;
condition_stop = 20;
increment_var = 'y';
goto increment;
loop_y_end:
increment_val = x;
condition_stop = 10;
increment_var = 'x';
goto increment;
loop_x_end:
halt;
increment:
increment_val++;
if (increment_var == 'x')
x = increment_val;
if (increment_var == 'y')
y = increment_val;
condition_val = increment_val;
condition_var = increment_var;
check_condition:
if (condition_val < condition_stop)
goto pass_condition:
if (condition_var == 'x')
goto loop_x_end;
if (condition_var == 'y')
goto loop_y_end;
pass_condition:
if (condition_var == 'x')
goto loop_x_body;
if (condition_var == 'y')
goto loop_y_body;