libcxx/include/__random/log2.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___RANDOM_LOG2_H
#define _LIBCPP___RANDOM_LOG2_H

#include <__config>
#include <cstddef>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <unsigned long long _Xp, size_t _Rp>
struct __log2_imp
{
    static const size_t value = _Xp & ((unsigned long long)(1) << _Rp) ? _Rp
                                           : __log2_imp<_Xp, _Rp - 1>::value;
};

template <unsigned long long _Xp>
struct __log2_imp<_Xp, 0>
{
    static const size_t value = 0;
};

template <size_t _Rp>
struct __log2_imp<0, _Rp>
{
    static const size_t value = _Rp + 1;
};

template <class _UIntType, _UIntType _Xp>
struct __log2
{
    static const size_t value = __log2_imp<_Xp,
                                         sizeof(_UIntType) * __CHAR_BIT__ - 1>::value;
};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANDOM_LOG2_H