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: ed25519.go
    path of file: ./repos/awless/vendor/golang.org/x/crypto/ed25519
    
    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.

// Package ed25519 implements the Ed25519 signature algorithm. See
// https://ed25519.cr.yp.to/.
//
// These functions are also compatible with the “Ed25519” function defined in
// RFC 8032.
package ed25519

// This code is a port of the public domain, “ref10” implementation of ed25519
// from SUPERCOP.

import (
	"bytes"
	"crypto"
	cryptorand "crypto/rand"
	"crypto/sha512"
	"errors"
	"io"
	"strconv"

	"golang.
    
func GenerateKey(rand io.Reader) (publicKey PublicKey, privateKey PrivateKey, err error) {
	if rand == nil {
		rand = cryptorand.Reader
	}

	privateKey = make([]byte, PrivateKeySize)
	publicKey = make([]byte, PublicKeySize)
	_, err = io.ReadFull(rand, privateKey[:32])
	if err != nil {
		return nil, nil, err
	}

	digest := sha512.Sum512(privateKey[:32])
	digest[0] &= 248
	digest[31] &= 127
	digest[31] |= 64

	var A edwards25519.ExtendedGroupElement
	var hBytes [32]byte
	copy(hBytes[:], digest[:])
	edwards25519.GeScalarMultBase(&A, &hBytes)
	var publicKeyBytes [32]byte
	A.ToBytes(&publicKeyBytes)

	copy(privateKey[32:], publicKeyBytes[:])
	copy(publicKey, publicKeyBytes[:])

	return publicKey, privateKey, nil
}