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: secretbox.go
    path of file: ./repos/awless/vendor/golang.org/x/crypto/nacl/secretbox
    
    the code of the file until where you have to start completion: // Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
Package secretbox encrypts and authenticates small messages.

Secretbox uses XSalsa20 and Poly1305 to encrypt and auth
    
func setup(subKey *[32]byte, counter *[16]byte, nonce *[24]byte, key *[32]byte) {
	// We use XSalsa20 for encryption so first we need to generate a
	// key and nonce with HSalsa20.
	var hNonce [16]byte
	copy(hNonce[:], nonce[:])
	salsa.HSalsa20(subKey, &hNonce, key, &salsa.Sigma)

	// The final 8 bytes of the original nonce form the new nonce.
	copy(counter[:], nonce[16:])
}