Source: xxhash_unsafe.go in package github.com/cespare/xxhash/v2

+build !appengine

This file encapsulates usage of unsafe. xxhash_safe.go contains the safe implementations.


package xxhash

import (
	"reflect"
	"unsafe"
)

Notes: See https://groups.google.com/d/msg/golang-nuts/dcjzJy-bSpw/tcZYBzQqAQAJ for some discussion about these unsafe conversions. In the future it's possible that compiler optimizations will make these unsafe operations unnecessary: https://golang.org/issue/2205. Both of these wrapper functions still incur function call overhead since they will not be inlined. We could write Go/asm copies of Sum64 and Digest.Write for strings to squeeze out a bit more speed. Mid-stack inlining should eventually fix this.

Sum64String computes the 64-bit xxHash digest of s. It may be faster than Sum64([]byte(s)) by avoiding a copy.

func Sum64String(s string) uint64 {
	var b []byte
	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
	bh.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
	bh.Len = len(s)
	bh.Cap = len(s)
	return Sum64(b)
}

WriteString adds more data to d. It always returns len(s), nil. It may be faster than Write([]byte(s)) by avoiding a copy.

func (d *Digest) WriteString(s string) (n int, err error) {
	var b []byte
	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
	bh.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
	bh.Len = len(s)
	bh.Cap = len(s)
	return d.Write(b)