diff --git a/bitwise.hpp b/bitwise.hpp
index e79be09a..96c98022 100644
--- a/bitwise.hpp
+++ b/bitwise.hpp
@@ -33,13 +33,24 @@ const uint8_t BITMASK_6BITS = 0x3F;
 const uint8_t BITMASK_7BITS = 0x7F;
 const uint8_t BITMASK_8BITS = 0xFF;
 
+#define MODT(x) ((x) % (sizeof (T) * 8))
 
 template <typename T>
-T
+constexpr T
 rotatel (const T &value, size_t magnitude) {
-    magnitude %= sizeof (T) * 8;
-    return (value << magnitude) | (value >> sizeof (value) * 8 - magnitude);
+    return (value << MODT (magnitude)) |
+           (value >> sizeof (value) * 8 - MODT (magnitude));
 }
 
+
+template <typename T>
+constexpr T
+rotater (const T &value, size_t magnitude) {
+    return (value >> MODT (magnitude)) |
+           (value << sizeof (value) * 8 - MODT (magnitude));
+}
+
+#undef MODT
+
 #endif 
 
diff --git a/test/bitwise.cpp b/test/bitwise.cpp
index 7085899a..5b9d7627 100644
--- a/test/bitwise.cpp
+++ b/test/bitwise.cpp
@@ -7,15 +7,28 @@ main (int, char**) {
     CHECK_EQ (rotatel (uint8_t (0xF0), 4), 0x0F);
     CHECK_EQ (rotatel (uint8_t (0x0F), 8), 0x0F);
 
+    CHECK_EQ (rotater (uint8_t (0x0F), 0), 0x0F);
+    CHECK_EQ (rotater (uint8_t (0x0F), 4), 0xF0);
+    CHECK_EQ (rotater (uint8_t (0xF0), 4), 0x0F);
+    CHECK_EQ (rotater (uint8_t (0x0F), 8), 0x0F);
+
     CHECK_EQ (rotatel (uint16_t (0xABCD),  0), 0xABCD);
     CHECK_EQ (rotatel (uint16_t (0xABCD),  4), 0xBCDA);
     CHECK_EQ (rotatel (uint16_t (0xABCD),  8), 0xCDAB);
     CHECK_EQ (rotatel (uint16_t (0xABCD), 12), 0xDABC);
     CHECK_EQ (rotatel (uint16_t (0xABCD), 16), 0xABCD);
 
+    CHECK_EQ (rotater (uint16_t (0xABCD),  0), 0xABCD);
+    CHECK_EQ (rotater (uint16_t (0xABCD),  4), 0xDABC);
+    CHECK_EQ (rotater (uint16_t (0xABCD),  8), 0xCDAB);
+    CHECK_EQ (rotater (uint16_t (0xABCD), 12), 0xBCDA);
+    CHECK_EQ (rotater (uint16_t (0xABCD), 16), 0xABCD);
+
     CHECK_EQ (rotatel (uint32_t (0x12345670), 12), 0x45670123);
+    CHECK_EQ (rotater (uint32_t (0x12345670), 12), 0x67012345);
 
     CHECK_EQ (rotatel (uint64_t (0x1234567890ABCDEF), 12), 0x4567890ABCDEF123);
+    CHECK_EQ (rotater (uint64_t (0x1234567890ABCDEF), 12), 0xDEF1234567890ABC);
 
     return 0;
 }