Question

I am new here so apologies if I did the post in a wrong way.

I was wondering if someone could please explain why is C so slow with function calling ?

Its easy to give a shallow answer to the standard question about Recursive Fibonacci, but I would appreciate if I knew the “deeper” reason as deep as possible.

Thanks.

Edit1 : Sorry for that mistake. I misunderstood an article in Wiki.

Answer 1

When you make a function call, your program has to put several registers on the stack, maybe push some more stuff, and mess with the stack pointer. That’s about all for what can be “slow”. Which is, actually, pretty fast. About 10 machine instructions on an x86_64 platform.

It’s slow if your code is sparse and your functions are very small. This is the case of the Fibonacci function. However, you have to make a difference between “slow calls” and “slow algorithm”: calculating the Fibonacci suite with a recursive implementation is pretty much the slowest straightforward way of doing it. There is almost as much code involved in the function body than in the function prologue and epilogue (where pushing and popping takes place).

There are cases in which calling functions will actually make your code faster overall. When you deal with large functions and your registers are crowded, the compiler may have a rough time deciding in which register to store data. However, isolating code inside a function call will simplify the compiler’s task of deciding which register to use.

So, no, C calls are not slow.