Changes in src/Common/utility.h [8ca60e4:5bf685f]

File:

• src/Common/utility.h (modified) (1 diff)

src/Common/utility.h

@@ -111 +111 @@
 };
 
+// -----------------------------------------------------------------------------
+// O(1) polymorphic integer ilog2, using clz, which returns the number of leading 0-bits, starting at the most
+// significant bit (single instruction on x86)
+
+template<typename T>
+inline
+#if defined(__GNUC__) && __GNUC__ > 4
+constexpr
+#endif
+T ilog2(const T & t) {
+        if(std::is_integral<T>::value) {
+                const constexpr int r = sizeof(t) * __CHAR_BIT__ - 1;
+                if( sizeof(T) == sizeof(unsigned       int) ) return r - __builtin_clz  ( t );
+                if( sizeof(T) == sizeof(unsigned      long) ) return r - __builtin_clzl ( t );
+                if( sizeof(T) == sizeof(unsigned long long) ) return r - __builtin_clzll( t );
+        }
+        assert(false);
+        return -1;
+} // ilog2
+
 // Local Variables: //
 // tab-width: 4 //