You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: xor.go
    path of file: ./repos/goHackTools/vendor/golang.org/x/crypto/chacha20
    
    the code of the file until where you have to start completion: // Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// lice
    
func addXor(dst, src []byte, a, b uint32) {
	_, _ = src[3], dst[3] // bounds check elimination hint
	if unaligned {
		// The compiler should optimize this code into
		// 32-bit unaligned little endian loads and stores.
		// TODO: delete once the compiler does a reliably
		// good job with the generic code below.
		// See issue #25111 for more details.
		v := uint32(src[0])
		v |= uint32(src[1]) << 8
		v |= uint32(src[2]) << 16
		v |= uint32(src[3]) << 24
		v ^= a + b
		dst[0] = byte(v)
		dst[1] = byte(v >> 8)
		dst[2] = byte(v >> 16)
		dst[3] = byte(v >> 24)
	} else {
		a += b
		dst[0] = src[0] ^ byte(a)
		dst[1] = src[1] ^ byte(a>>8)
		dst[2] = src[2] ^ byte(a>>16)
		dst[3] = src[3] ^ byte(a>>24)
	}
}