Changes in src/Common/utility.h [babeeda:9dc31c10]

File:

• src/Common/utility.h (modified) (2 diffs)

src/Common/utility.h

@@ -9 +9 @@
 // Author           : Richard C. Bilson
 // Created On       : Mon May 18 07:44:20 2015
-// Last Modified By : Andrew Beach
-// Last Modified On : Thr Aug 17 11:38:00 2017
-// Update Count     : 34
+// Last Modified By : Peter A. Buhr
+// Last Modified On : Thu Apr 19 16:21:44 2018
+// Update Count     : 37
 //
 
@@ -436 +436 @@
 }
 
+// -----------------------------------------------------------------------------
+// O(1) polymorphic integer log2, using clz, which returns the number of leading 0-bits, starting at the most
+// significant bit (single instruction on x86)
+
+template<typename T>
+inline constexpr T log2(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 );
+        } // if
+        return -1;
+}