diff --git a/math/fast_power.cpp b/math/fast_power.cpp
index 0ffbcd40d..f69a90e4c 100644
--- a/math/fast_power.cpp
+++ b/math/fast_power.cpp
@@ -21,16 +21,17 @@
 /**
  * algorithm implementation for \f$a^b\f$
  */
-double fast_power_recursive(int64_t a, int64_t b) {
+template <typename T>
+double fast_power_recursive(T a, T b) {
     // negative power. a^b = 1 / (a^-b)
     if (b < 0) return 1.0 / fast_power_recursive(a, -b);
 
     if (b == 0) return 1;
-    int64_t bottom = fast_power_recursive(a, b >> 1);
+    T bottom = fast_power_recursive(a, b >> 1);
     // Since it is integer division b/2 = (b-1)/2 where b is odd.
     // Therefore, case2 is easily solved by integer division.
 
-    int64_t result;
+    double result;
     if ((b & 1) == 0)  // case1
         result = bottom * bottom;
     else  // case2
@@ -42,7 +43,8 @@ double fast_power_recursive(int64_t a, int64_t b) {
     Same algorithm with little different formula.
     It still calculates in O(logN)
 */
-double fast_power_linear(int64_t a, int64_t b) {
+template <typename T>
+double fast_power_linear(T a, T b) {
     // negative power. a^b = 1 / (a^-b)
     if (b < 0) return 1.0 / fast_power_linear(a, -b);