After reading Xan’s article The Cyclomatic Horror From Outer Space analyzing the complexity of some GTK functions, I was curious and I wanted to run the same test in the GIMP source tree in order to see what parts of the code would be the hardest to test. This test is very simple and can be summarized as counting the number of decision points in every function in a program (so you get an idea of the number of possible code paths).
I did as suggested and I started with “apt-get install pmccabe“, followed by “pmccabe app/*/*.c | sort -nr | head -10” to get the 10 functions with the highest (worst) results. This gave me the following table:
| Cyclomatic complexity | Lines of code | Function name |
|---|---|---|
| 113 | 892 | gimp_display_shell_canvas_tool_events |
| 100 | 123 | layers_actions_update |
| 69 | 416 | update_box_rgb |
| 61 | 359 | border_region |
| 60 | 445 | siox_foreground_extract |
| 56 | 452 | render_image_tile_fault |
| 54 | 327 | combine_inten_a_and_inten_a_pixels |
| 53 | 194 | gimp_plug_in_procedure_add_menu_path |
| 47 | 275 | gimp_drawable_offset |
| 46 | 240 | gimp_vector_tool_oper_update |
According to the CMU page on cyclomatic complexity, numbers between 21 and 50 reveal a “complex, high risk program” and numbers above 50 only occur in an “untestable program (very high risk)“.
What does this mean for GIMP? Not much. But if you touch one of these functions, please be careful… you might break things and it will be very hard to find where the bugs are hiding in that code.