Go's Memset Equivalent: How to Efficiently Initialize Arrays with Non-Zero Values?

Go Analog for Memset

Question:

Go programmers seek an efficient method analogous to C 's memset to initialize arrays with non-zero values, as basic loops can be slow.

Answer:

While Go lacks an explicit memset function, there are optimized approaches that emulate its functionality.

Loop-Based Solution:

The simplest alternative is a loop that iterates through the array, assigning the desired value to each element:

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

Copy-Based Solution:

Go's optimized copy() function can be leveraged to initialize arrays quickly. By setting the first element manually and repeatedly copying the filled portion, the number of iterations is reduced to log(n):

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])
    }
}

Performance Comparison:

For small arrays, the loop-based solution is marginally faster. However, as the array size grows, the copy-based solution becomes significantly faster due to its reduced number of iterations.

Benchmark Results:

Array Size	Loop-Based	Copy-Based
100 elements	1.15x slower
1,000 elements	2.5x slower
10,000 elements	2x slower
100,000 elements	1.5x slower

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