Golang implement of `java.lang.String` hashCode() https://en.wikipedia.org/wiki/Java_hashCode()

hashcode.go

package hashcode

import "hash"

const Size = 4

func NewHash() hash.Hash32 {
	var s sum32 = 0
	return &s
}

type sum32 uint32

func (sum32) BlockSize() int  { return 1 }
func (sum32) Size() int       { return Size }
func (h *sum32) Reset()       { *h = 0 }
func (h sum32) Sum32() uint32 { return uint32(h) }
func (h sum32) Sum(in []byte) []byte {
	s := h.Sum32()
	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
}
func (h *sum32) Write(p []byte) (n int, err error) {
	s := h.Sum32()
	for _, pp := range p {
		s = 31*s + uint32(pp)
	}
	*h = sum32(s)
	return len(p), nil
}