How to Efficiently Initialize Arrays in Go: memset Alternatives?

Analog of memset in Go

In C , the memset function efficiently initializes an array with a specified value. Go, however, lacks direct memset support. This article explores several alternative approaches to achieve similar functionality.

Iterative Loop Solution

A straightforward implementation using a loop is:

func memsetLoop(a []int, v int) {
    for i := range a {
        a[i] = v
    }
}

Copy-Based Solution

An optimized approach leverages the efficient copy() function:

func memsetRepeat(a []int, v int) {
    if len(a) == 0 {
        return
    }
    a[0] = v
    for bp := 1; bp < len(a); bp *= 2 {
        copy(a[bp:], a[:bp])
    }
}

This solution resembles the implementation of bytes.Repeat(). For creating a new []byte filled with the same value, bytes.Repeat() is recommended.

Benchmark Comparison

Performance benchmarks reveal the superiority of memsetRepeat() over memsetLoop() as the array size increases:

Array Size	memsetLoop	memsetRepeat	Improvement
100	~1.15x slower	~1.15x faster
1,000	~2.5x slower	~2.5x faster
10,000	~2x slower	~2x faster
100,000	~1.5x slower	~1.5x faster

At around 3800-4000 elements, memsetRepeat() offers a significant ~3.2x performance boost.

Conclusion

While memset is not natively supported in Go, memsetLoop() and memsetRepeat() provide efficient alternatives for initializing arrays with non-zero values. memsetRepeat(), utilizing copy(), emerges as the optimal solution for larger arrays.

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