new file (needed by dynamic_bitset)

[SVN r22651]

include/boost/pending/integer_log2.hpp

@@ -0,0 +1,96 @@
+// -------------------------------------
+// integer_log2.hpp
+//
+//   Gives the integer part of the logarithm, in base 2, of a
+// given number. Behavior is undefined if the argument is <= 0.
+//
+//
+//       (C) Copyright Gennaro Prota 2003 - 2004.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          http://www.boost.org/LICENSE_1_0.txt)
+//
+// ------------------------------------------------------
+
+
+
+#ifndef BOOST_INTEGER_LOG2_HPP_GP_20030301
+#define BOOST_INTEGER_LOG2_HPP_GP_20030301
+
+#include <cassert>
+#include "boost/limits.hpp"
+#include "boost/config.hpp"
+
+
+namespace boost {
+ namespace detail {
+
+  template <typename T>
+  int integer_log2_impl(T x, int n) {
+
+      int result = 0;
+
+      while (x != 1) {
+
+          const T t = x >> n;
+          if (t) {
+              result += n;
+              x = t;
+          }
+          n /= 2;
+
+      }
+
+      return result;
+  }
+
+
+
+  // helper to find the maximum power of two
+  // less than p (more involved than necessary,
+  // to avoid PTS)
+  //
+  template <int p, int n>
+  struct max_pow2_less {
+
+      enum { c = 2*n < p };
+
+      BOOST_STATIC_CONSTANT(int, value =
+          c ? (max_pow2_less< c*p, 2*c*n>::value) : n);
+
+  };
+
+  template <>
+  struct max_pow2_less<0, 0> {
+
+      BOOST_STATIC_CONSTANT(int, value = 0);
+  };
+
+ } // detail
+
+
+ // ---------
+ // integer_log2
+ // ---------------
+ //
+ template <typename T>
+ int integer_log2(T x) {
+
+     assert(x > 0);
+
+     const int n = detail::max_pow2_less<
+                    std::numeric_limits<T> :: digits, 4
+                    > :: value;
+
+     return detail::integer_log2_impl(x, n);
+
+ }
+
+
+
+}
+
+
+
+#endif // include guard