Key sizes 4 and 8 have special case hashing code.
They are intended for int32, int64, and pointers, but your [4]byte and
[8]byte take advantage of it as well.
On Sunday, March 26, 2023 at 3:05:52 AM UTC-7 Amit Lavon wrote:
> Hi gophers,
>
> Some code I am writing uses byte-arrays ([X]byte) as keys in a map. I
> benchmarked the performance of map operations using different X's and found
> that 4 and 8 are about twice as fast compared to 5, 6, 7 (see below).
>
> Can someone explain this phenomenon?
> I'd like to learn about it so I can take it in consideration when choosing
> key types.
>
>
> Code:
>
> type byteArray interface {
> [4]byte | [5]byte | [6]byte | [7]byte | [8]byte
> }
>
> func benchmarkMaps[T byteArray](b *testing.B) {
> m := map[T]int{}
> var t T
> for i := 0; i < b.N; i++ {
> m[t]++
> }
> }
>
> func BenchmarkMaps(b *testing.B) {
> b.Run("4", benchmarkMaps[[4]byte])
> b.Run("5", benchmarkMaps[[5]byte])
> b.Run("6", benchmarkMaps[[6]byte])
> b.Run("7", benchmarkMaps[[7]byte])
> b.Run("8", benchmarkMaps[[8]byte])
> }
>
> Results:
>
> 4: 17.01 ns/op
> 5: 36.02 ns/op
> 6: 38.24 ns/op
> 7: 29.92 ns/op
> 8: 16.58 ns/op
>
> go1.20
>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/golang-nuts/baa4ed12-faa6-409c-825c-bd632a180c8cn%40googlegroups.com.
