Have you written very long functions? If so, why?

Question

Hi,

I am writing an academic project about extremely long functions in the Linux kernel.

For that purpose, I am looking for examples for real-life functions that are extremely long (few hundreds of lines of code), that you don't consider bad programming (i.e., they won't benefit from decomposition or usage of a dispatch table).

Have you ever written or seen such a code? Can you post or link to it, and give explanation of why is it so long?

I have been getting amazing help from the community here - any idea that will be taken into the project will be properly credited.

Thanks,

Udi

Answer 1

The longest functions that I have ever written all have one thing in common, a very large switch statement. There are times, when you have to switch on a long list of items and it would only make things harder to understand if you tried to refactor some of the options into a separate function. Having large switch statements makes the Cyclomatic complexity go through the roof, but it is often better than the alternative implementations.

Answer 2

A previous job: An extremely long case statement, IIRC 1000+ lines. This was long before objects. Each option was only a few lines long. Breaking it up would have made it less clear. There were actually a pair of such routines doing different things to the same underlying set of data types.

Sorry, I don't have the code anymore and it isn't mine to post, anyway.

Answer 3

I could imagine that when speed is important (such as when holding some sort of lock in the kernel) you would not want to break up a function because of the overhead due to making a functional call. When compiled, parameters have to be pushed onto the stack and data has to be popped off before returning. Therefor you may have a large function for efficiency reasons.

Answer 4

The longest function that I didn't see as being horrible would be the key method of a custom CPU VM. As with @epotter, this involved a big switch statement. In fact I'd say a lot of method that I find resist being cleanly broken down or improved in readability involve switch statements.

Answer 5

Unfortunately, you won't often find this type of subroutine checked in or posted somewhere if it's auto-generated during a build step using some sort of code generator.

So look for projects that have C generated from another language.

Answer 6

It was the last one before I got fired.

Answer 7

Beside the performance, I think the size of the call stack in Kernel space is 8K (please verify the size). Also, as far as I know, code in kernel is fairly specific. If some code is unlikely to be re-used in the future why bother make it a function considering function call overhead.