1package rand
 2
 3import (
 4	"crypto/rand"
 5	"fmt"
 6	"io"
 7	"math/big"
 8)
 9
10func init() {
11	Reader = rand.Reader
12}
13
14// Reader provides a random reader that can reset during testing.
15var Reader io.Reader
16
17// Int63n returns a int64 between zero and value of max, read from an io.Reader source.
18func Int63n(reader io.Reader, max int64) (int64, error) {
19	bi, err := rand.Int(reader, big.NewInt(max))
20	if err != nil {
21		return 0, fmt.Errorf("failed to read random value, %w", err)
22	}
23
24	return bi.Int64(), nil
25}
26
27// CryptoRandInt63n returns a random int64 between zero and value of max
28// obtained from the crypto rand source.
29func CryptoRandInt63n(max int64) (int64, error) {
30	return Int63n(Reader, max)
31}