Append consecutive slices, on same underlying array

append_test.go

package tstappend

import "testing"

const N = 8192

func appendBytes(a, b []byte) []byte {
	if len(b) == 0 {
		return a
	}
	if cap(a) >= len(a)+len(b) && &a[:len(a)+1][len(a)] == &b[0] {
		return a[:len(a)+len(b)]
	}
	return append(a, b...)
}

func BenchmarkAppendBytes(b *testing.B) {
	bf := make([]byte, N)
	bf0 := bf[0:0]
	b.ResetTimer()
	var bf1 []byte
	for i := 0; i < b.N; i++ {
		bf1 = appendBytes(bf0, bf)
	}
	bf0 = bf1
}

func BenchmarkAppend(b *testing.B) {
	bf := make([]byte, N)
	bf0 := make([]byte, 0, N)
	var bf1 []byte
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		bf1 = append(bf0, bf...)
	}
	bf0 = bf1
}

func BenchmarkCopy(b *testing.B) {
	bf := make([]byte, N)
	bf0 := make([]byte, N)
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		copy(bf0, bf)
	}
}

Results:

go test -bench=.
testing: warning: no tests to run
BenchmarkAppendBytes-4      2000000000           0.32 ns/op
BenchmarkAppend-4            3000000           415 ns/op
BenchmarkCopy-4              3000000           424 ns/op
PASS
ok      github.com/npat-efault/tst/tstappend    4.128s