diff --git a/include/xemmai/heap.h b/include/xemmai/heap.h
index c0a9044..9e84c46 100644
--- a/include/xemmai/heap.h
+++ b/include/xemmai/heap.h
@@ -16,10 +16,6 @@ namespace xemmai
 template<typename T>
 class t_heap
 {
-	static constexpr size_t f_log(size_t a_x)
-	{
-		return a_x > 1 ? f_log(a_x >> 1) + 1 : 0;
-	}
 	static void* f_map(size_t a_n)
 	{
 #ifdef __unix__
@@ -139,10 +135,10 @@ class t_heap
 	constexpr T* f_allocate_medium(size_t a_size);
 
 public:
-	static constexpr size_t V_UNIT = 2 << f_log(sizeof(T) - 1);
+	static constexpr size_t V_UNIT = std::bit_ceil(sizeof(T));
 	static_assert(V_UNIT >> 1 < sizeof(T));
 	static_assert(V_UNIT >= sizeof(T));
-	static constexpr size_t V_RANKX = sizeof(void*) * 8 - f_log(V_UNIT);
+	static constexpr size_t V_RANKX = std::countl_zero(V_UNIT - 1);
 	static_assert((V_UNIT << (V_RANKX - 1)) - 1 == ~size_t(0) >> 1);
 	static_assert((V_UNIT << V_RANKX) - 1 == ~size_t(0));