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+// -------------- Boost static_log2.hpp header file ----------------------- //
+//
+// Copyright (C) 2001 Daryle Walker.
+// Copyright (C) 2003 Vesa Karvonen.
+// Copyright (C) 2003 Gennaro Prota.
+//
+// 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)
+//
+// ---------------------------------------------------
+// See http://www.boost.org/libs/integer for documentation.
+// ------------------------------------------------------------------------- //
+
+
+#ifndef BOOST_INTEGER_STATIC_LOG2_HPP
+#define BOOST_INTEGER_STATIC_LOG2_HPP
+
+#include "cutl/details/boost/integer_fwd.hpp" // for cutl_details_boost::intmax_t
+
+namespace cutl_details_boost {
+
+ namespace detail {
+
+ namespace static_log2_impl {
+
+ // choose_initial_n<>
+ //
+ // Recursively doubles its integer argument, until it
+ // becomes >= of the "width" (C99, 6.2.6.2p4) of
+ // static_log2_argument_type.
+ //
+ // Used to get the maximum power of two less then the width.
+ //
+ // Example: if on your platform argument_type has 48 value
+ // bits it yields n=32.
+ //
+ // It's easy to prove that, starting from such a value
+ // of n, the core algorithm works correctly for any width
+ // of static_log2_argument_type and that recursion always
+ // terminates with x = 1 and n = 0 (see the algorithm's
+ // invariant).
+
+ typedef cutl_details_boost::static_log2_argument_type argument_type;
+ typedef cutl_details_boost::static_log2_result_type result_type;
+
+ template <result_type n>
+ struct choose_initial_n {
+
+ BOOST_STATIC_CONSTANT(bool, c = (argument_type(1) << n << n) != 0);
+ BOOST_STATIC_CONSTANT(
+ result_type,
+ value = !c*n + choose_initial_n<2*c*n>::value
+ );
+
+ };
+
+ template <>
+ struct choose_initial_n<0> {
+ BOOST_STATIC_CONSTANT(result_type, value = 0);
+ };
+
+
+
+ // start computing from n_zero - must be a power of two
+ const result_type n_zero = 16;
+ const result_type initial_n = choose_initial_n<n_zero>::value;
+
+ // static_log2_impl<>
+ //
+ // * Invariant:
+ // 2n
+ // 1 <= x && x < 2 at the start of each recursion
+ // (see also choose_initial_n<>)
+ //
+ // * Type requirements:
+ //
+ // argument_type maybe any unsigned type with at least n_zero + 1
+ // value bits. (Note: If larger types will be standardized -e.g.
+ // unsigned long long- then the argument_type typedef can be
+ // changed without affecting the rest of the code.)
+ //
+
+ template <argument_type x, result_type n = initial_n>
+ struct static_log2_impl {
+
+ BOOST_STATIC_CONSTANT(bool, c = (x >> n) > 0); // x >= 2**n ?
+ BOOST_STATIC_CONSTANT(
+ result_type,
+ value = c*n + (static_log2_impl< (x>>c*n), n/2 >::value)
+ );
+
+ };
+
+ template <>
+ struct static_log2_impl<1, 0> {
+ BOOST_STATIC_CONSTANT(result_type, value = 0);
+ };
+
+ }
+ } // detail
+
+
+
+ // --------------------------------------
+ // static_log2<x>
+ // ----------------------------------------
+
+ template <static_log2_argument_type x>
+ struct static_log2 {
+
+ BOOST_STATIC_CONSTANT(
+ static_log2_result_type,
+ value = detail::static_log2_impl::static_log2_impl<x>::value
+ );
+
+ };
+
+
+ template <>
+ struct static_log2<0> { };
+
+}
+
+
+
+#endif // include guard