refactor fast primitive root test

internal/lib/lib.go

@@ -159,22 +159,24 @@ func PrimitiveRootFast(modulus *big.Int, tpf map[string]*big.Int) (*big.Int, err
 			continue
 		}
 
-		isPrimitive := true
+		if isPrimitiveRoot(g, modulus, phi, tpf) {
-		for p := range tpf {
-			// we already know factors are valid from computing phi
-			k, _ := new(big.Int).SetString(p, 10)
-			k.Div(phi, k)
-			k.Exp(g, k, modulus)
-			if k.Cmp(big.NewInt(1)) == 0 {
-				isPrimitive = false
-				break
-			}
-		}
-
-		if isPrimitive {
 			return g, nil
 		}
 	}
 
 	return nil, errors.New("no primitive root")
 }
+
+func isPrimitiveRoot(g *big.Int, modulus *big.Int, phi *big.Int, tpf map[string]*big.Int) bool {
+	for p := range tpf {
+		// we already know factors are valid from computing phi
+		k, _ := new(big.Int).SetString(p, 10)
+		k.Div(phi, k)
+		k.Exp(g, k, modulus)
+		if k.Cmp(big.NewInt(1)) == 0 {
+			return false
+		}
+	}
+
+	return true
+}