third_party/llvm-project/libcxx/include/__random/generate_canonical.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_GENERATE_CANONICAL_H
#define _LIBCPP___RANDOM_GENERATE_CANONICAL_H

#include <__config>
#include <__random/log2.h>
#include <cstdint>
#include <initializer_list>
#include <limits>

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

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

// generate_canonical

template<class _RealType, size_t __bits, class _URNG>
_LIBCPP_HIDE_FROM_ABI _RealType
generate_canonical(_URNG& __g)
{
    const size_t _Dt = numeric_limits<_RealType>::digits;
    const size_t __b = _Dt < __bits ? _Dt : __bits;
#ifdef _LIBCPP_CXX03_LANG
    const size_t __logR = __log2<uint64_t, _URNG::_Max - _URNG::_Min + uint64_t(1)>::value;
#else
    const size_t __logR = __log2<uint64_t, _URNG::max() - _URNG::min() + uint64_t(1)>::value;
#endif
    const size_t __k = __b / __logR + (__b % __logR != 0) + (__b == 0);
    const _RealType _Rp = static_cast<_RealType>(_URNG::max() - _URNG::min()) + _RealType(1);
    _RealType __base = _Rp;
    _RealType _Sp = __g() - _URNG::min();
    for (size_t __i = 1; __i < __k; ++__i, __base *= _Rp)
        _Sp += (__g() - _URNG::min()) * __base;
    return _Sp / __base;
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___RANDOM_GENERATE_CANONICAL_H