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 generate_canonical(_URNG& __g) {
  31   const size_t __dt = numeric_limits<_RealType>::digits;
  32   const size_t __b  = __dt < __bits ? __dt : __bits;
  33 #ifdef _LIBCPP_CXX03_LANG
  34   const size_t __log_r = __log2<uint64_t, _URNG::_Max - _URNG::_Min + uint64_t(1)>::value;
  35 #else
  36   const size_t __log_r = __log2<uint64_t, _URNG::max() - _URNG::min() + uint64_t(1)>::value;
  37 #endif
  38   const size_t __k     = __b / __log_r + (__b % __log_r != 0) + (__b == 0);
  39   const _RealType __rp = static_cast<_RealType>(_URNG::max() - _URNG::min()) + _RealType(1);
  40   _RealType __base     = __rp;
  41   _RealType __sp       = __g() - _URNG::min();
  42   for (size_t __i = 1; __i < __k; ++__i, __base *= __rp)
  43     __sp += (__g() - _URNG::min()) * __base;
  44   return __sp / __base;
  45 }
  46
  47 _LIBCPP_END_NAMESPACE_STD
  48
  49 _LIBCPP_POP_MACROS
  50
  51 #endif // _LIBCPP___RANDOM_GENERATE_CANONICAL_H