diff --git a/permute.hh b/permute.hh
index 82ee3a9..283ffbd 100644
--- a/permute.hh
+++ b/permute.hh
@@ -35,12 +35,14 @@ public:
 	}
 };
 
-template <typename TYPE>
-void BitReversalPermute(TYPE *array, int n) {
-	for (int i = 0, j = 0; i < n - 1; ++i) {
+template <int SIZE, typename TYPE>
+static void BitReversalPermute(TYPE *array)
+{
+	static_assert(SIZE > 0 && (SIZE & (SIZE - 1)) == 0, "SIZE not power of two");
+	for (int i = 0, j = 0; i < SIZE - 1; ++i) {
 		if (i < j)
 			std::swap(array[i], array[j]);
-		int k = n >> 1;
+		int k = SIZE >> 1;
 		while (j & k) {
 			j ^= k;
 			k >>= 1;