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39
40#ifndef QRANDOM_H
41#define QRANDOM_H
42
43#include <QtCore/qglobal.h>
44#include <algorithm> // for std::generate
45#include <random> // for std::mt19937
46
47#ifdef min
48# undef min
49#endif
50#ifdef max
51# undef max
52#endif
53
54QT_BEGIN_NAMESPACE
55
56class QRandomGenerator
57{
58 // restrict the template parameters to unsigned integers 32 bits wide or larger
59 template <typename UInt> using IfValidUInt =
60 typename std::enable_if<std::is_unsigned<UInt>::value && sizeof(UInt) >= sizeof(uint), bool>::type;
61public:
62 QRandomGenerator(quint32 seedValue = 1)
63 : QRandomGenerator(&seedValue, 1)
64 {}
65 template <qsizetype N> QRandomGenerator(const quint32 (&seedBuffer)[N])
66 : QRandomGenerator(seedBuffer, seedBuffer + N)
67 {}
68 QRandomGenerator(const quint32 *seedBuffer, qsizetype len)
69 : QRandomGenerator(seedBuffer, seedBuffer + len)
70 {}
71 Q_CORE_EXPORT QRandomGenerator(std::seed_seq &sseq) noexcept;
72 Q_CORE_EXPORT QRandomGenerator(const quint32 *begin, const quint32 *end);
73
74 // copy constructor & assignment operator (move unnecessary)
75 Q_CORE_EXPORT QRandomGenerator(const QRandomGenerator &other);
76 Q_CORE_EXPORT QRandomGenerator &operator=(const QRandomGenerator &other);
77
78 friend Q_CORE_EXPORT bool operator==(const QRandomGenerator &rng1, const QRandomGenerator &rng2);
79 friend bool operator!=(const QRandomGenerator &rng1, const QRandomGenerator &rng2)
80 {
81 return !(rng1 == rng2);
82 }
83
84 quint32 generate()
85 {
86 quint32 ret;
87 fillRange(&ret, 1);
88 return ret;
89 }
90
91 quint64 generate64()
92 {
93 quint32 buf[2];
94 fillRange(buf);
95 return buf[0] | (quint64(buf[1]) << 32);
96 }
97
98 double generateDouble()
99 {
100 // IEEE 754 double precision has:
101 // 1 bit sign
102 // 10 bits exponent
103 // 53 bits mantissa
104 // In order for our result to be normalized in the range [0, 1), we
105 // need exactly 53 bits of random data. Use generate64() to get enough.
106 quint64 x = generate64();
107 quint64 limit = Q_UINT64_C(1) << std::numeric_limits<double>::digits;
108 x >>= std::numeric_limits<quint64>::digits - std::numeric_limits<double>::digits;
109 return double(x) / double(limit);
110 }
111
112 double bounded(double highest)
113 {
114 return generateDouble() * highest;
115 }
116
117 quint32 bounded(quint32 highest)
118 {
119 quint64 value = generate();
120 value *= highest;
121 value /= (max)() + quint64(1);
122 return quint32(value);
123 }
124
125 quint32 bounded(quint32 lowest, quint32 highest)
126 {
127 Q_ASSERT(highest > lowest);
128 return bounded(highest - lowest) + lowest;
129 }
130
131 int bounded(int highest)
132 {
133 Q_ASSERT(highest > 0);
134 return int(bounded(0U, quint32(highest)));
135 }
136
137 int bounded(int lowest, int highest)
138 {
139 return bounded(highest - lowest) + lowest;
140 }
141
142 template <typename UInt, IfValidUInt<UInt> = true>
143 void fillRange(UInt *buffer, qsizetype count)
144 {
145 _fillRange(buffer, buffer + count);
146 }
147
148 template <typename UInt, size_t N, IfValidUInt<UInt> = true>
149 void fillRange(UInt (&buffer)[N])
150 {
151 _fillRange(buffer, buffer + N);
152 }
153
154 // API like std::seed_seq
155 template <typename ForwardIterator>
156 void generate(ForwardIterator begin, ForwardIterator end)
157 {
158 std::generate(begin, end, [this]() { return generate(); });
159 }
160
161 void generate(quint32 *begin, quint32 *end)
162 {
163 _fillRange(begin, end);
164 }
165
166 // API like std:: random engines
167 typedef quint32 result_type;
168 result_type operator()() { return generate(); }
169 void seed(quint32 s = 1) { *this = { s }; }
170 void seed(std::seed_seq &sseq) noexcept { *this = { sseq }; }
171 Q_CORE_EXPORT void discard(unsigned long long z);
172 static Q_DECL_CONSTEXPR result_type min() { return std::numeric_limits<result_type>::min(); }
173 static Q_DECL_CONSTEXPR result_type max() { return std::numeric_limits<result_type>::max(); }
174
175 static inline Q_DECL_CONST_FUNCTION QRandomGenerator *system();
176 static inline Q_DECL_CONST_FUNCTION QRandomGenerator *global();
177 static inline QRandomGenerator securelySeeded();
178
179protected:
180 enum System {};
181 QRandomGenerator(System);
182
183private:
184 Q_CORE_EXPORT void _fillRange(void *buffer, void *bufferEnd);
185
186 friend class QRandomGenerator64;
187 struct SystemGenerator;
188 struct SystemAndGlobalGenerators;
189 using RandomEngine = std::mersenne_twister_engine<quint32,
190 32,624,397,31,0x9908b0df,11,0xffffffff,7,0x9d2c5680,15,0xefc60000,18,1812433253>;
191
192 union Storage {
193 uint dummy;
194#ifdef Q_COMPILER_UNRESTRICTED_UNIONS
195 RandomEngine twister;
196 RandomEngine &engine() { return twister; }
197 const RandomEngine &engine() const { return twister; }
198#else
199 std::aligned_storage<sizeof(RandomEngine), Q_ALIGNOF(RandomEngine)>::type buffer;
200 RandomEngine &engine() { return reinterpret_cast<RandomEngine &>(buffer); }
201 const RandomEngine &engine() const { return reinterpret_cast<const RandomEngine &>(buffer); }
202#endif
203
204 Q_STATIC_ASSERT_X(std::is_trivially_destructible<RandomEngine>::value,
205 "std::mersenne_twister not trivially destructible as expected");
206 Q_DECL_CONSTEXPR Storage();
207 };
208 uint type;
209 Storage storage;
210};
211
212class QRandomGenerator64 : public QRandomGenerator
213{
214 QRandomGenerator64(System);
215public:
216 // unshadow generate() overloads, since we'll override.
217 using QRandomGenerator::generate;
218 quint64 generate() { return generate64(); }
219
220 typedef quint64 result_type;
221 result_type operator()() { return generate64(); }
222
223#ifndef Q_QDOC
224 QRandomGenerator64(quint32 seedValue = 1)
225 : QRandomGenerator(seedValue)
226 {}
227 template <qsizetype N> QRandomGenerator64(const quint32 (&seedBuffer)[N])
228 : QRandomGenerator(seedBuffer)
229 {}
230 QRandomGenerator64(const quint32 *seedBuffer, qsizetype len)
231 : QRandomGenerator(seedBuffer, len)
232 {}
233 QRandomGenerator64(std::seed_seq &sseq) noexcept
234 : QRandomGenerator(sseq)
235 {}
236 QRandomGenerator64(const quint32 *begin, const quint32 *end)
237 : QRandomGenerator(begin, end)
238 {}
239 QRandomGenerator64(const QRandomGenerator &other) : QRandomGenerator(other) {}
240
241 void discard(unsigned long long z)
242 {
243 Q_ASSERT_X(z * 2 > z, "QRandomGenerator64::discard",
244 "Overflow. Are you sure you want to skip over 9 quintillion samples?");
245 QRandomGenerator::discard(z * 2);
246 }
247
248 static Q_DECL_CONSTEXPR result_type min() { return std::numeric_limits<result_type>::min(); }
249 static Q_DECL_CONSTEXPR result_type max() { return std::numeric_limits<result_type>::max(); }
250 static Q_DECL_CONST_FUNCTION Q_CORE_EXPORT QRandomGenerator64 *system();
251 static Q_DECL_CONST_FUNCTION Q_CORE_EXPORT QRandomGenerator64 *global();
252 static Q_CORE_EXPORT QRandomGenerator64 securelySeeded();
253#endif // Q_QDOC
254};
255
256inline QRandomGenerator *QRandomGenerator::system()
257{
258 return QRandomGenerator64::system();
259}
260
261inline QRandomGenerator *QRandomGenerator::global()
262{
263 return QRandomGenerator64::global();
264}
265
266QRandomGenerator QRandomGenerator::securelySeeded()
267{
268 return QRandomGenerator64::securelySeeded();
269}
270
271QT_END_NAMESPACE
272
273#endif // QRANDOM_H
274