mirror of
https://github.com/yuzu-emu/ext-boost.git
synced 2024-12-22 17:55:38 +00:00
128 lines
3.5 KiB
C++
128 lines
3.5 KiB
C++
// -------------- 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
|