i found this code, and use it on hash.Hash
// copy an interface value using reflect (here for pointers to interfaces)
func clone(i interface{}) interface{} {
indirect := reflect.Indirect(reflect.ValueOf(i))
newIndirect := reflect.New(indirect.Type())
newIndirect.Elem().Set(reflect.ValueOf(indirect.Interface()))
return newIndirect.Interface()
}
like this;
branchHasher = clone(hasher).(hash.Hash)
On Wednesday, 8 November 2017 12:54:18 UTC, Christian LeMoussel wrote:
>
> Hi,
>
> I want to calculate hash on 3 strings. First string is always the same,
> the other may vary.
> The first approach is to calculate the hash each time for the 3 strings (
> BenchmarkHash)
> Another approach would be to calculate once for the first string, and then
> reuse this hash to calculate the hash with the other 2 strings
> (BenchmarkCopyHash)
> The difficulty is that sha256.New() returns a pointer, we have to copy
> the first hash. To do this, I created the function copyHash()
> But the performances are not exceptional.
>
> Do you have another idea to do this in efficient way?
>
>
> BenchmarkHash-8 1000000 1761
> ns/op 176 B/op 4 allocs/op
> BenchmarkCopyHash-8 1000000 1519
> ns/op 240 B/op 4 allocs/op
>
>
> var m1 = strings.Repeat("a", 64)
> var m2 = strings.Repeat("b", 48)
> var m3 = strings.Repeat("c", 32)
>
> func BenchmarkHash(b *testing.B) {
> var (
> d hash.Hash
> )
>
> d = sha256.New()
> for n := 0; n < b.N; n++ {
> d.Reset()
> d.Write([]byte(m1))
> d.Write([]byte(m2))
> d.Write([]byte(m3))
> d.Sum(nil)
> }
> }
> func BenchmarkCopyHash(b *testing.B) {
> var (
> d1 hash.Hash
> d2 hash.Hash
> )
>
> d1 = sha256.New()
> d1.Write([]byte(m1))
>
> for n := 0; n < b.N; n++ {
> d2 = copyHash(d1)
> d2.Write([]byte(m2))
> d2.Write([]byte(m3))
> d2.Sum(nil)
> }
> }
>
> func copyHash(src hash.Hash) hash.Hash {
> typ := reflect.TypeOf(src).Elem()
> val := reflect.ValueOf(src).Elem()
> elem := reflect.New(typ).Elem()
> elem.Set(val)
> return elem.Addr().Interface().(hash.Hash)
> }
>
>
>
>
>
>
>
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