From 52300cf40252566a083c9495029133f520d3a4a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Sat, 12 Jan 2013 18:24:39 +0100
Subject: [PATCH] Math: function for base-2 logarithm.

Verbatim copy from Corrade, might be better to have it here too
(possibly some SIMD optimizations?).
---
 src/Math/Math.cpp          | 7 +++++++
 src/Math/Math.h            | 9 +++++++++
 src/Math/Test/MathTest.cpp | 8 +++++++-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/Math/Math.cpp b/src/Math/Math.cpp
index 7e432040f..d2cdd0ce6 100644
--- a/src/Math/Math.cpp
+++ b/src/Math/Math.cpp
@@ -17,6 +17,13 @@
 
 namespace Magnum { namespace Math {
 
+std::uint32_t log2(std::uint32_t number) {
+    std::uint32_t log = 0;
+    while(number >>= 1)
+        ++log;
+    return log;
+}
+
 std::uint32_t log(std::uint32_t base, std::uint32_t number) {
     std::uint32_t log = 0;
     while(number /= base)
diff --git a/src/Math/Math.h b/src/Math/Math.h
index 9bc03cf82..7a9004fe1 100644
--- a/src/Math/Math.h
+++ b/src/Math/Math.h
@@ -58,10 +58,19 @@ template<std::uint32_t exponent, class T> inline constexpr T pow(T base) {
     return Implementation::Pow<exponent>()(base);
 }
 
+/**
+ * @brief Base-2 integral logarithm
+ *
+ * Returns integral logarithm of given number with base `2`.
+ * @see log()
+ */
+std::uint32_t MAGNUM_EXPORT log2(std::uint32_t number);
+
 /**
  * @brief Integral logarithm
  *
  * Returns integral logarithm of given number with given base.
+ * @see log2()
  */
 std::uint32_t MAGNUM_EXPORT log(std::uint32_t base, std::uint32_t number);
 
diff --git a/src/Math/Test/MathTest.cpp b/src/Math/Test/MathTest.cpp
index e14aeaf18..044bfa350 100644
--- a/src/Math/Test/MathTest.cpp
+++ b/src/Math/Test/MathTest.cpp
@@ -28,6 +28,7 @@ class MathTest: public Corrade::TestSuite::Tester {
         void clamp();
         void pow();
         void log();
+        void log2();
 };
 
 MathTest::MathTest() {
@@ -35,7 +36,8 @@ MathTest::MathTest() {
              &MathTest::denormalize,
              &MathTest::clamp,
              &MathTest::pow,
-             &MathTest::log);
+             &MathTest::log,
+             &MathTest::log2);
 }
 
 void MathTest::normalize() {
@@ -105,6 +107,10 @@ void MathTest::log() {
     CORRADE_COMPARE(Math::log(256, 2), 0ul);
 }
 
+void MathTest::log2() {
+    CORRADE_COMPARE(Math::log2(2153), 11);
+}
+
 }}}
 
 CORRADE_TEST_MAIN(Magnum::Math::Test::MathTest)