What is loop unrolling in C and how does it improve performance?

What is loop unrolling in C and how does it improve performance?

Loop unrolling is an optimization technique that reduces the overhead of loop control by increasing the number of operations within the loop body. This can lead to improved performance by decreasing the number of iterations and minimizing branching.

Can you give me an example of loop unrolling in C?

Sure! Here's a simple example:

for (int i = 0; i < n; i++) {
    sum += array[i];
}

This can be unrolled to:

for (int i = 0; i < n; i += 4) {
    sum += array[i];
    sum += array[i + 1];
    sum += array[i + 2];
    sum += array[i + 3];
}

This reduces the number of iterations and can enhance performance.

Are there any downsides to loop unrolling?

Yes, there are some downsides. Loop unrolling can increase code size, which may lead to cache misses. Additionally, it can make the code less readable and harder to maintain.

When should I consider using loop unrolling?

You should consider using loop unrolling when performance is critical, especially in tight loops where the overhead of loop control is significant. However, always profile your code to ensure it provides a benefit.