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: chacha20poly1305_amd64.go
    path of file: ./repos/agones/vendor/golang.org/x/crypto/chacha20poly1305
    
    the code of the file until where you have to start completion: // Copyright 2016 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.

//go:build gc && !purego

package chacha20poly1305

import (
	"encoding/binary"

	"golang.org/x/crypto/internal/alias"
	"golang.org/x/sys/cpu"
)

//go:noescape
func chacha20Poly1305Open(dst []byte, 
    
func setupState(state *[16]uint32, key *[32]byte, nonce []byte) {
	state[0] = 0x61707865
	state[1] = 0x3320646e
	state[2] = 0x79622d32
	state[3] = 0x6b206574

	state[4] = binary.LittleEndian.Uint32(key[0:4])
	state[5] = binary.LittleEndian.Uint32(key[4:8])
	state[6] = binary.LittleEndian.Uint32(key[8:12])
	state[7] = binary.LittleEndian.Uint32(key[12:16])
	state[8] = binary.LittleEndian.Uint32(key[16:20])
	state[9] = binary.LittleEndian.Uint32(key[20:24])
	state[10] = binary.LittleEndian.Uint32(key[24:28])
	state[11] = binary.LittleEndian.Uint32(key[28:32])

	state[12] = 0
	state[13] = binary.LittleEndian.Uint32(nonce[0:4])
	state[14] = binary.LittleEndian.Uint32(nonce[4:8])
	state[15] = binary.LittleEndian.Uint32(nonce[8:12])
}