xref: /openbsd-src/gnu/llvm/libcxx/include/__random/linear_congruential_engine.h (revision 4bdff4bed0e3d54e55670334c7d0077db4170f86)

//===----------------------------------------------------------------------===//
//
// 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>
_LIBCPP_HIDE_FROM_ABI 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 - _UIntType(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>
_LIBCPP_HIDE_FROM_ABI 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