CODEWITHSUNDEEP
c++if-statementfunction-call
Xeo
Xeo

Reputation: 131799

What is faster: noop function call or if statement?

I got a function pointer for a deleter, but most of the time, the deleter is not gonna be needed, only when I maintain an internal copy of something. Currently I do that with a noop deleter function:

class MyClass{
public:
  // bind object
  template<class Type>
  void Bind(Type* obj){
    Cleanup();
    object_ = obj;
  }

  // bind object with internal copy
  template<class Type>
  void Bind(Type obj){
    Cleanup();
    object_ = new Type(obj);
    deleter = &Deleter<Type>;
  }

private:
  template<class Type>
  static void Deleter(void* obj_ptr){
    Type* obj = static_cast<Type*>(obj_ptr);
    delete obj;
  }

  static void NoopDeleter(void* unused){
  }

  void Cleanup(){
    (*deleter_)(object_);
    object_ = 0;
    deleter_ = &NoopDeleter;
  }

  typedef void (*DeleterFunc)(void*);

  void* object_;
  DeleterFunc deleter_;
};

Now the obvious other choice would be to set it to 0 when not needed, and check in the Cleanup function with if(deleter_ != 0) (*deleter_)(object_).
Now during the coding, it just came to my mind "Hm, which version would be faster?", so it's more of a personal interest rather than optimization. Sorry if the question sounds kinda stupid, but it kinda bugs me and I really want to know. Thanks for any answers in advance!

Upvotes: 3

Views: 1128

Answers (2)

Tony Delroy
Tony Delroy

Reputation: 106106

A variable comparison to 0 will be faster than a function call (typically a single cycle), particularly given the variable has to be loaded into a register to make the function call anyway. Overheads include adjusting the stack, pushing object_ and the return address, calling into the function....

Upvotes: 1

Vagrant
Vagrant

Reputation: 1716

Function call has to setup a stack frame. All the if-statement has to do is execute a single machine instruction. Maybe two, depending on the rchitecture of the machine.

Upvotes: 3

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