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| author | Remko Tronçon <git@el-tramo.be> | 2009-06-01 08:48:42 (GMT) |
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| committer | Remko Tronçon <git@el-tramo.be> | 2009-06-01 09:24:28 (GMT) |
| commit | 2812bddd81f8a1b804c7460f4e14cd0aa393d129 (patch) | |
| tree | d46294f35150c4f0f43deaf2d31fceaf945ae715 /3rdParty/Boost/boost/integer/static_log2.hpp | |
| download | swift-contrib-2812bddd81f8a1b804c7460f4e14cd0aa393d129.zip swift-contrib-2812bddd81f8a1b804c7460f4e14cd0aa393d129.tar.bz2 | |
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Diffstat (limited to '3rdParty/Boost/boost/integer/static_log2.hpp')
| -rw-r--r-- | 3rdParty/Boost/boost/integer/static_log2.hpp | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/3rdParty/Boost/boost/integer/static_log2.hpp b/3rdParty/Boost/boost/integer/static_log2.hpp new file mode 100644 index 0000000..19e048b --- /dev/null +++ b/3rdParty/Boost/boost/integer/static_log2.hpp @@ -0,0 +1,132 @@ +// -------------- 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/config.hpp" // for BOOST_STATIC_CONSTANT + +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 unsigned long argument_type; + typedef int result_type; + + + template <result_type n> + struct choose_initial_n { + + enum { 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 { + + enum { 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> + // ---------------------------------------- + + typedef detail::static_log2_impl::argument_type static_log2_argument_type; + typedef detail::static_log2_impl::result_type static_log2_result_type; + + + 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 |