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llvm-project/libcxx/include/__random/linear_congruential_engine.h
Louis Dionne 368faacac7 [libc++] Revert "Protect users from relying on detail headers" & related changes 
This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9,
which were related to the original commit). As landed, 5aaefa51 had
unintended consequences on some downstream bots and didn't have proper
coverage upstream due to a few subtle things. Implementing this is
something we should do in libc++, however we'll first need to address
a few issues listed in https://reviews.llvm.org/D106124#3349710.

Differential Revision: https://reviews.llvm.org/D120683
2022-03-01 08:20:24 -05:00

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//===----------------------------------------------------------------------===//
//
// 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_LINEAR_CONGRUENTIAL_ENGINE_H
#define _LIBCPP___RANDOM_LINEAR_CONGRUENTIAL_ENGINE_H
#include <__config>
#include <__random/is_seed_sequence.h>
#include <cstdint>
#include <iosfwd>
#include <type_traits>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_PUSH_MACROS
#include <__undef_macros>
_LIBCPP_BEGIN_NAMESPACE_STD
template <unsigned long long __a, unsigned long long __c,
unsigned long long __m, unsigned long long _Mp,
bool _MightOverflow = (__a != 0 && __m != 0 && __m-1 > (_Mp-__c)/__a),
bool _OverflowOK = ((__m | (__m-1)) > __m), // m = 2^n
bool _SchrageOK = (__a != 0 && __m != 0 && __m % __a <= __m / __a)> // r <= q
struct __lce_alg_picker
{
static_assert(__a != 0 || __m != 0 || !_MightOverflow || _OverflowOK || _SchrageOK,
"The current values of a, c, and m cannot generate a number "
"within bounds of linear_congruential_engine.");
static _LIBCPP_CONSTEXPR const bool __use_schrage = _MightOverflow &&
!_OverflowOK &&
_SchrageOK;
};
template <unsigned long long __a, unsigned long long __c,
unsigned long long __m, unsigned long long _Mp,
bool _UseSchrage = __lce_alg_picker<__a, __c, __m, _Mp>::__use_schrage>
struct __lce_ta;
// 64
template <unsigned long long __a, unsigned long long __c, unsigned long long __m>
struct __lce_ta<__a, __c, __m, (unsigned long long)(~0), true>
{
typedef unsigned long long result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
// Schrage's algorithm
const result_type __q = __m / __a;
const result_type __r = __m % __a;
const result_type __t0 = __a * (__x % __q);
const result_type __t1 = __r * (__x / __q);
__x = __t0 + (__t0 < __t1) * __m - __t1;
__x += __c - (__x >= __m - __c) * __m;
return __x;
}
};
template <unsigned long long __a, unsigned long long __m>
struct __lce_ta<__a, 0, __m, (unsigned long long)(~0), true>
{
typedef unsigned long long result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
// Schrage's algorithm
const result_type __q = __m / __a;
const result_type __r = __m % __a;
const result_type __t0 = __a * (__x % __q);
const result_type __t1 = __r * (__x / __q);
__x = __t0 + (__t0 < __t1) * __m - __t1;
return __x;
}
};
template <unsigned long long __a, unsigned long long __c, unsigned long long __m>
struct __lce_ta<__a, __c, __m, (unsigned long long)(~0), false>
{
typedef unsigned long long result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
return (__a * __x + __c) % __m;
}
};
template <unsigned long long __a, unsigned long long __c>
struct __lce_ta<__a, __c, 0, (unsigned long long)(~0), false>
{
typedef unsigned long long result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
return __a * __x + __c;
}
};
// 32
template <unsigned long long _Ap, unsigned long long _Cp, unsigned long long _Mp>
struct __lce_ta<_Ap, _Cp, _Mp, unsigned(~0), true>
{
typedef unsigned result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
const result_type __a = static_cast<result_type>(_Ap);
const result_type __c = static_cast<result_type>(_Cp);
const result_type __m = static_cast<result_type>(_Mp);
// Schrage's algorithm
const result_type __q = __m / __a;
const result_type __r = __m % __a;
const result_type __t0 = __a * (__x % __q);
const result_type __t1 = __r * (__x / __q);
__x = __t0 + (__t0 < __t1) * __m - __t1;
__x += __c - (__x >= __m - __c) * __m;
return __x;
}
};
template <unsigned long long _Ap, unsigned long long _Mp>
struct __lce_ta<_Ap, 0, _Mp, unsigned(~0), true>
{
typedef unsigned result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
const result_type __a = static_cast<result_type>(_Ap);
const result_type __m = static_cast<result_type>(_Mp);
// Schrage's algorithm
const result_type __q = __m / __a;
const result_type __r = __m % __a;
const result_type __t0 = __a * (__x % __q);
const result_type __t1 = __r * (__x / __q);
__x = __t0 + (__t0 < __t1) * __m - __t1;
return __x;
}
};
template <unsigned long long _Ap, unsigned long long _Cp, unsigned long long _Mp>
struct __lce_ta<_Ap, _Cp, _Mp, unsigned(~0), false>
{
typedef unsigned result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
const result_type __a = static_cast<result_type>(_Ap);
const result_type __c = static_cast<result_type>(_Cp);
const result_type __m = static_cast<result_type>(_Mp);
return (__a * __x + __c) % __m;
}
};
template <unsigned long long _Ap, unsigned long long _Cp>
struct __lce_ta<_Ap, _Cp, 0, unsigned(~0), false>
{
typedef unsigned result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
const result_type __a = static_cast<result_type>(_Ap);
const result_type __c = static_cast<result_type>(_Cp);
return __a * __x + __c;
}
};
// 16
template <unsigned long long __a, unsigned long long __c, unsigned long long __m, bool __b>
struct __lce_ta<__a, __c, __m, (unsigned short)(~0), __b>
{
typedef unsigned short result_type;
_LIBCPP_INLINE_VISIBILITY
static result_type next(result_type __x)
{
return static_cast<result_type>(__lce_ta<__a, __c, __m, unsigned(~0)>::next(__x));
}
};
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
class _LIBCPP_TEMPLATE_VIS linear_congruential_engine;
template <class _CharT, class _Traits,
class _Up, _Up _Ap, _Up _Cp, _Up _Np>
_LIBCPP_INLINE_VISIBILITY
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
const linear_congruential_engine<_Up, _Ap, _Cp, _Np>&);
template <class _CharT, class _Traits,
class _Up, _Up _Ap, _Up _Cp, _Up _Np>
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
linear_congruential_engine<_Up, _Ap, _Cp, _Np>& __x);
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
class _LIBCPP_TEMPLATE_VIS linear_congruential_engine
{
public:
// types
typedef _UIntType result_type;
private:
result_type __x_;
static _LIBCPP_CONSTEXPR const result_type _Mp = result_type(~0);
static_assert(__m == 0 || __a < __m, "linear_congruential_engine invalid parameters");
static_assert(__m == 0 || __c < __m, "linear_congruential_engine invalid parameters");
static_assert(is_unsigned<_UIntType>::value, "_UIntType must be unsigned type");
public:
static _LIBCPP_CONSTEXPR const result_type _Min = __c == 0u ? 1u: 0u;
static _LIBCPP_CONSTEXPR const result_type _Max = __m - 1u;
static_assert(_Min < _Max, "linear_congruential_engine invalid parameters");
// engine characteristics
static _LIBCPP_CONSTEXPR const result_type multiplier = __a;
static _LIBCPP_CONSTEXPR const result_type increment = __c;
static _LIBCPP_CONSTEXPR const result_type modulus = __m;
_LIBCPP_INLINE_VISIBILITY
static _LIBCPP_CONSTEXPR result_type min() {return _Min;}
_LIBCPP_INLINE_VISIBILITY
static _LIBCPP_CONSTEXPR result_type max() {return _Max;}
static _LIBCPP_CONSTEXPR const result_type default_seed = 1u;
// constructors and seeding functions
#ifndef _LIBCPP_CXX03_LANG
_LIBCPP_INLINE_VISIBILITY
linear_congruential_engine() : linear_congruential_engine(default_seed) {}
_LIBCPP_INLINE_VISIBILITY
explicit linear_congruential_engine(result_type __s) { seed(__s); }
#else
_LIBCPP_INLINE_VISIBILITY
explicit linear_congruential_engine(result_type __s = default_seed) {
seed(__s);
}
#endif
template<class _Sseq>
_LIBCPP_INLINE_VISIBILITY
explicit linear_congruential_engine(_Sseq& __q,
typename enable_if<__is_seed_sequence<_Sseq, linear_congruential_engine>::value>::type* = 0)
{seed(__q);}
_LIBCPP_INLINE_VISIBILITY
void seed(result_type __s = default_seed)
{seed(integral_constant<bool, __m == 0>(),
integral_constant<bool, __c == 0>(), __s);}
template<class _Sseq>
_LIBCPP_INLINE_VISIBILITY
typename enable_if
<
__is_seed_sequence<_Sseq, linear_congruential_engine>::value,
void
>::type
seed(_Sseq& __q)
{__seed(__q, integral_constant<unsigned,
1 + (__m == 0 ? (sizeof(result_type) * __CHAR_BIT__ - 1)/32
: (__m > 0x100000000ull))>());}
// generating functions
_LIBCPP_INLINE_VISIBILITY
result_type operator()()
{return __x_ = static_cast<result_type>(__lce_ta<__a, __c, __m, _Mp>::next(__x_));}
_LIBCPP_INLINE_VISIBILITY
void discard(unsigned long long __z) {for (; __z; --__z) operator()();}
friend _LIBCPP_INLINE_VISIBILITY
bool operator==(const linear_congruential_engine& __x,
const linear_congruential_engine& __y)
{return __x.__x_ == __y.__x_;}
friend _LIBCPP_INLINE_VISIBILITY
bool operator!=(const linear_congruential_engine& __x,
const linear_congruential_engine& __y)
{return !(__x == __y);}
private:
_LIBCPP_INLINE_VISIBILITY
void seed(true_type, true_type, result_type __s) {__x_ = __s == 0 ? 1 : __s;}
_LIBCPP_INLINE_VISIBILITY
void seed(true_type, false_type, result_type __s) {__x_ = __s;}
_LIBCPP_INLINE_VISIBILITY
void seed(false_type, true_type, result_type __s) {__x_ = __s % __m == 0 ?
1 : __s % __m;}
_LIBCPP_INLINE_VISIBILITY
void seed(false_type, false_type, result_type __s) {__x_ = __s % __m;}
template<class _Sseq>
void __seed(_Sseq& __q, integral_constant<unsigned, 1>);
template<class _Sseq>
void __seed(_Sseq& __q, integral_constant<unsigned, 2>);
template <class _CharT, class _Traits,
class _Up, _Up _Ap, _Up _Cp, _Up _Np>
friend
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
const linear_congruential_engine<_Up, _Ap, _Cp, _Np>&);
template <class _CharT, class _Traits,
class _Up, _Up _Ap, _Up _Cp, _Up _Np>
friend
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
linear_congruential_engine<_Up, _Ap, _Cp, _Np>& __x);
};
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
_LIBCPP_CONSTEXPR const typename linear_congruential_engine<_UIntType, __a, __c, __m>::result_type
linear_congruential_engine<_UIntType, __a, __c, __m>::multiplier;
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
_LIBCPP_CONSTEXPR const typename linear_congruential_engine<_UIntType, __a, __c, __m>::result_type
linear_congruential_engine<_UIntType, __a, __c, __m>::increment;
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
_LIBCPP_CONSTEXPR const typename linear_congruential_engine<_UIntType, __a, __c, __m>::result_type
linear_congruential_engine<_UIntType, __a, __c, __m>::modulus;
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
_LIBCPP_CONSTEXPR const typename linear_congruential_engine<_UIntType, __a, __c, __m>::result_type
linear_congruential_engine<_UIntType, __a, __c, __m>::default_seed;
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
template<class _Sseq>
void
linear_congruential_engine<_UIntType, __a, __c, __m>::__seed(_Sseq& __q,
integral_constant<unsigned, 1>)
{
const unsigned __k = 1;
uint32_t __ar[__k+3];
__q.generate(__ar, __ar + __k + 3);
result_type __s = static_cast<result_type>(__ar[3] % __m);
__x_ = __c == 0 && __s == 0 ? result_type(1) : __s;
}
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
template<class _Sseq>
void
linear_congruential_engine<_UIntType, __a, __c, __m>::__seed(_Sseq& __q,
integral_constant<unsigned, 2>)
{
const unsigned __k = 2;
uint32_t __ar[__k+3];
__q.generate(__ar, __ar + __k + 3);
result_type __s = static_cast<result_type>((__ar[3] +
((uint64_t)__ar[4] << 32)) % __m);
__x_ = __c == 0 && __s == 0 ? result_type(1) : __s;
}
template <class _CharT, class _Traits,
class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
inline _LIBCPP_INLINE_VISIBILITY
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
const linear_congruential_engine<_UIntType, __a, __c, __m>& __x)
{
__save_flags<_CharT, _Traits> __lx(__os);
typedef basic_ostream<_CharT, _Traits> _Ostream;
__os.flags(_Ostream::dec | _Ostream::left);
__os.fill(__os.widen(' '));
return __os << __x.__x_;
}
template <class _CharT, class _Traits,
class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
linear_congruential_engine<_UIntType, __a, __c, __m>& __x)
{
__save_flags<_CharT, _Traits> __lx(__is);
typedef basic_istream<_CharT, _Traits> _Istream;
__is.flags(_Istream::dec | _Istream::skipws);
_UIntType __t;
__is >> __t;
if (!__is.fail())
__x.__x_ = __t;
return __is;
}
typedef linear_congruential_engine<uint_fast32_t, 16807, 0, 2147483647>
minstd_rand0;
typedef linear_congruential_engine<uint_fast32_t, 48271, 0, 2147483647>
minstd_rand;
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS
#endif // _LIBCPP___RANDOM_LINEAR_CONGRUENTIAL_ENGINE_H
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