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37 * \brief The uniform integer distribution
39 * Portable version of the uniform integer that generates the same sequence
40 * on all platforms. Since stdlibc++ and libc++ provide different sequences
41 * we prefer this one so unit tests produce the same values on all platforms.
43 * \author Erik Lindahl <erik.lindahl@gmail.com>
45 * \ingroup module_random
48 #ifndef GMX_RANDOM_UNIFORMINTDISTRIBUTION_H
49 #define GMX_RANDOM_UNIFORMINTDISTRIBUTION_H
54 #include "gromacs/math/functions.h"
55 #include "gromacs/utility/basedefinitions.h"
56 #include "gromacs/utility/classhelpers.h"
57 #include "gromacs/utility/gmxassert.h"
62 /*! \brief Uniform integer distribution
64 * The C++ standard library does provide this distribution, but even
65 * though they all sample from the correct distribution different standard
66 * library implementations appear to return different sequences of numbers
67 * for the same random number generator. To make it easier to use GROMACS
68 * unit tests that depend on random numbers we have our own implementation.
70 * \tparam IntType Integer type, int by default.
72 template<class IntType = int>
73 class UniformIntDistribution
76 /*! \brief Type of values returned */
77 typedef IntType result_type;
79 /*! \brief Uniform int distribution parameters */
82 /*! \brief Lower end of range (inclusive) */
84 /*! \brief Upper end of range (inclusive) */
88 /*! \brief Reference back to the distribution class */
89 typedef UniformIntDistribution distribution_type;
91 /*! \brief Construct parameter block
93 * \param a Lower end of range (inclusive)
94 * \param b Upper end of range (inclusive)
96 explicit param_type(result_type a = 0, result_type b = std::numeric_limits<result_type>::max()) :
100 GMX_RELEASE_ASSERT(a <= b, "The uniform integer distribution requires a<=b");
103 /*! \brief Return lower range */
104 result_type a() const { return a_; }
105 /*! \brief Return upper range */
106 result_type b() const { return b_; }
108 /*! \brief True if two parameter sets will return the same uniform int distribution.
110 * \param x Instance to compare with.
112 bool operator==(const param_type& x) const
114 // rangeBits is a function of a & b, so it does not have to be tested
115 return a_ == x.a_ && b_ == x.b_;
118 /*! \brief True if two parameter sets will return different uniform int distributions
120 * \param x Instance to compare with.
122 bool operator!=(const param_type& x) const { return !operator==(x); }
126 /*! \brief Construct new distribution with given integer parameters.
128 * \param a Lower end of range (inclusive)
129 * \param b Upper end of range (inclusive)
131 explicit UniformIntDistribution(result_type a = 0,
132 result_type b = std::numeric_limits<result_type>::max()) :
133 param_(param_type(a, b)),
135 savedRandomBitsLeft_(0)
139 /*! \brief Construct new distribution from parameter class
141 * \param param Parameter class as defined inside gmx::UniformIntDistribution.
143 explicit UniformIntDistribution(const param_type& param) :
146 savedRandomBitsLeft_(0)
150 /*! \brief Flush all internal saved values */
151 void reset() { savedRandomBitsLeft_ = 0; }
153 /*! \brief Return values from uniform int distribution with internal parameters
155 * \tparam Rng Uniform random engine class
157 * \param g Random engine
160 result_type operator()(Rng& g)
162 return (*this)(g, param_);
165 /*! \brief Return value from uniform int distribution with given parameters
167 * \tparam Rng Uniform random engine class
169 * \param g Random engine
170 * \param param Parameters to use
173 result_type operator()(Rng& g, const param_type& param)
175 static_assert(sizeof(typename Rng::result_type) >= sizeof(uint32_t),
176 "The random engine result_type should be 32 or 64 bits");
178 result_type range = param.b() - param.a();
179 unsigned int rangeBits;
186 else if (range == std::numeric_limits<result_type>::max())
188 rangeBits = std::numeric_limits<result_type>::digits; // Use all bits in type
192 if (sizeof(result_type) == sizeof(uint32_t))
194 rangeBits = log2I(static_cast<uint32_t>(range));
198 rangeBits = log2I(range);
200 rangeBits += ((range >> rangeBits) > 0);
205 if (savedRandomBitsLeft_ < rangeBits)
207 savedRandomBits_ = static_cast<uint64_t>(g());
208 savedRandomBitsLeft_ = std::numeric_limits<typename Rng::result_type>::digits;
210 if (sizeof(typename Rng::result_type) == sizeof(uint32_t))
212 savedRandomBits_ <<= std::numeric_limits<uint32_t>::digits;
213 savedRandomBits_ |= g();
214 savedRandomBitsLeft_ += std::numeric_limits<uint32_t>::digits;
217 result = savedRandomBits_;
218 savedRandomBits_ >>= rangeBits;
219 result = result - (savedRandomBits_ << rangeBits);
220 savedRandomBitsLeft_ -= rangeBits;
221 } while (result > range);
223 return result + param.a();
226 /*! \brief Return the lower range uniform int distribution */
227 result_type a() const { return param_.a(); }
229 /*! \brief Return the upper range of the uniform int distribution */
230 result_type b() const { return param_.b(); }
232 /*! \brief Return the full parameter class of the uniform int distribution */
233 param_type param() const { return param_; }
235 /*! \brief Smallest value that can be returned from uniform int distribution */
236 result_type min() const { return a(); }
238 /*! \brief Largest value that can be returned from uniform int distribution */
239 result_type max() const { return b(); }
241 /*! \brief True if two uniform int distributions will produce the same values.
243 * \param x Instance to compare with.
245 bool operator==(const UniformIntDistribution& x) const { return param_ == x.param_; }
247 /*! \brief True if two uniform int distributions will produce different values.
249 * \param x Instance to compare with.
251 bool operator!=(const UniformIntDistribution& x) const { return !operator==(x); }
254 /*! \brief Internal value for parameters, can be overridden at generation time. */
256 /*! \brief Saved output from random engine, shifted tableBits right each time */
257 uint64_t savedRandomBits_;
258 /*! \brief Number of valid bits remaining i savedRandomBits_ */
259 unsigned int savedRandomBitsLeft_;
261 GMX_DISALLOW_COPY_AND_ASSIGN(UniformIntDistribution);
266 #endif // GMX_RANDOM_UNIFORMINTDISTRIBUTION_H