Add Int63n() and RandInt63n().

common/random.go

@@ -101,6 +101,10 @@ func RandInt63() int64 {
 	return grand.Int63()
 }
 
+func RandInt63n(n int64) int64 {
+	return grand.Int63n(n)
+}
+
 func RandUint16Exp() uint16 {
 	return grand.Uint16Exp()
 }
@@ -244,6 +248,14 @@ func (r *Rand) Int63() int64 {
 	return i63
 }
 
+// It is not safe for cryptographic usage.
+func (r *Rand) Int63n(n int64) int64 {
+	r.Lock()
+	i63n := r.rand.Int63n(n)
+	r.Unlock()
+	return i63n
+}
+
 // Distributed pseudo-exponentially to test for various cases
 // It is not safe for cryptographic usage.
 func (r *Rand) Uint16Exp() uint16 {