moby/vendor/github.com/aws/smithy-go/rand/rand.go

package rand

import (
	"crypto/rand"
	"fmt"
	"io"
	"math/big"
)

func init() {
	Reader = rand.Reader
}

// Reader provides a random reader that can reset during testing.
var Reader io.Reader

// Int63n returns a int64 between zero and value of max, read from an io.Reader source.
func Int63n(reader io.Reader, max int64) (int64, error) {
	bi, err := rand.Int(reader, big.NewInt(max))
	if err != nil {
		return 0, fmt.Errorf("failed to read random value, %w", err)
	}

	return bi.Int64(), nil
}

// CryptoRandInt63n returns a random int64 between zero and value of max
// obtained from the crypto rand source.
func CryptoRandInt63n(max int64) (int64, error) {
	return Int63n(Reader, max)
}