Updated boost to v1.55.0

[rsem.git] / boost / integer / static_log2.hpp

diff --git a/boost/integer/static_log2.hpp b/boost/integer/static_log2.hpp
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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 "boost/integer_fwd.hpp" // for boost::intmax_t
+
+namespace 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 boost::static_log2_argument_type argument_type;
+     typedef 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