What are the best practices for improving execution efficiency of C++ functions?

In order to improve the execution efficiency of C functions, best practices include: reducing unnecessary function calls; inlining small functions; optimizing loops (using range loops, register keywords, and avoiding function calls in loops); avoiding dynamic allocation ( Use memory pools and preallocated containers); use constant expressions.

Best practices for improving C function execution efficiency

In large and complex projects, the execution efficiency of functions is crucial. The following best practices can significantly improve the performance of C functions:

1. Reduce the number of function calls

• Try to avoid unnecessary function calls because they There will be overhead.
• Consider inlining small functions or moving function calls outside the loop.

2. Inline functions

• Use the inline keyword to inline small functions, which can eliminate the need for function calls overhead.
• Only inline simple functions that are called frequently, as inlining increases code size.

3. Optimize loops

• Use range loops (for (auto& element : container)) instead of iterator.
• Use the register keyword to store local variables in a register for faster access.
• Avoid making function calls in loops.

4. Avoid dynamic allocation

• Dynamic allocation (using new and delete) will Incur overhead.
• Consider using memory pools and pre-allocated containers to reduce dynamic allocation.

5. Use constant expressions

• to mark the expression as constexpr to enable the compiler to calculate value, thereby eliminating runtime overhead.
• Use constant variables instead of calculating the value each time.

Practical case: Optimizing Fibonacci sequence function

Consider the following unoptimized Fibonacci sequence function:

int fib(int n) {
  if (n <= 1) {
    return n;
  } else {
    return fib(n - 1) + fib(n - 2);
  }
}

By applying the above best practices, we can greatly improve its efficiency:

inline int fib(int n) {
  static const int fib_cache[] = {0, 1, 1};
  if (n <= 2) {
    return fib_cache[n];
  } else {
    register int prev = 1;
    register int current = 1;
    for (int i = 3; i <= n; ++i) {
      register int next = prev + current;
      prev = current;
      current = next;
    }
    return current;
  }
}

In the optimized function, we:

• utilize the constant cache to store the calculated value.
• Use register variables to optimize loop performance.
• Reduced unnecessary recursive calls.

Through these optimizations, the execution efficiency of the function is significantly improved, especially when entering large n values.

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