libcxx/include/__random/generate_canonical.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___RANDOM_GENERATE_CANONICAL_H
  10 #define _LIBCPP___RANDOM_GENERATE_CANONICAL_H
  11
  12 #include <__config>
  13 #include <__random/log2.h>
  14 #include <cstdint>
  15 #include <initializer_list>
  16 #include <limits>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_PUSH_MACROS
  23 #include <__undef_macros>
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 // generate_canonical
  28
  29 template<class _RealType, size_t __bits, class _URNG>
  30 _LIBCPP_HIDE_FROM_ABI _RealType
  31 generate_canonical(_URNG& __g)
  32 {
  33     const size_t __dt = numeric_limits<_RealType>::digits;
  34     const size_t __b = __dt < __bits ? __dt : __bits;
  35 #ifdef _LIBCPP_CXX03_LANG
  36     const size_t __log_r = __log2<uint64_t, _URNG::_Max - _URNG::_Min + uint64_t(1)>::value;
  37 #else
  38     const size_t __log_r = __log2<uint64_t, _URNG::max() - _URNG::min() + uint64_t(1)>::value;
  39 #endif
  40     const size_t __k = __b / __log_r + (__b % __log_r != 0) + (__b == 0);
  41     const _RealType __rp = static_cast<_RealType>(_URNG::max() - _URNG::min()) + _RealType(1);
  42     _RealType __base = __rp;
  43     _RealType __sp = __g() - _URNG::min();
  44     for (size_t __i = 1; __i < __k; ++__i, __base *= __rp)
  45         __sp += (__g() - _URNG::min()) * __base;
  46     return __sp / __base;
  47 }
  48
  49 _LIBCPP_END_NAMESPACE_STD
  50
  51 _LIBCPP_POP_MACROS
  52
  53 #endif // _LIBCPP___RANDOM_GENERATE_CANONICAL_H