diff --git a/maths.cpp b/maths.cpp
index 4e382600..4b5cbdd0 100644
--- a/maths.cpp
+++ b/maths.cpp
@@ -40,6 +40,18 @@ template bool is_pow2 (uint32_t);
 template bool is_pow2 (uint64_t);
 
 
+//-----------------------------------------------------------------------------
+template <typename T>
+T
+log2up (T v)
+{
+    return log2 ((v << 1) - 1);
+}
+
+template uint32_t log2up (uint32_t);
+template uint64_t log2up (uint64_t);
+
+
 //-----------------------------------------------------------------------------
 template <typename T>
 T
diff --git a/maths.hpp b/maths.hpp
index 19c44d75..0b9ad9d2 100644
--- a/maths.hpp
+++ b/maths.hpp
@@ -41,6 +41,11 @@ T
 log2 (T val) pure;
 
 
+template <typename T>
+T
+log2up (T val) pure;
+
+
 template <typename T>
 double
 rootsquare (T a, T b) pure;
diff --git a/test/maths/maths.cpp b/test/maths/maths.cpp
index c61026c0..4d70735f 100644
--- a/test/maths/maths.cpp
+++ b/test/maths/maths.cpp
@@ -45,5 +45,10 @@ main (int, char **) {
     CHECK_EQ (log2 (8u), 3);
     CHECK_EQ (log2 (1u), 0);
 
+    CHECK_EQ (log2   (9u), 3);
+    CHECK_EQ (log2up (9u), 4);
+    CHECK_EQ (log2up (8u), 3);
+    CHECK_EQ (log2up (1u), 0);
+
     return EXIT_SUCCESS;
 }