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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
53 #include "gromacs/math/functions.h"
54 #include "gromacs/utility/basedefinitions.h"
55 #include "gromacs/utility/classhelpers.h"
56 #include "gromacs/utility/gmxassert.h"
61 /*! \brief Uniform integer distribution
63 * The C++ standard library does provide this distribution, but even
64 * though they all sample from the correct distribution different standard
65 * library implementations appear to return different sequences of numbers
66 * for the same random number generator. To make it easier to use GROMACS
67 * unit tests that depend on random numbers we have our own implementation.
69 * \tparam IntType Integer type, int by default.
71 template<class IntType = int>
72 class UniformIntDistribution
75 /*! \brief Type of values returned */
76 typedef IntType result_type;
78 /*! \brief Uniform int distribution parameters */
81 /*! \brief Lower end of range (inclusive) */
83 /*! \brief Upper end of range (inclusive) */
87 /*! \brief Reference back to the distribution class */
88 typedef UniformIntDistribution distribution_type;
90 /*! \brief Construct parameter block
92 * \param a Lower end of range (inclusive)
93 * \param b Upper end of range (inclusive)
95 explicit param_type(result_type a = 0, result_type b = std::numeric_limits<result_type>::max()) :
99 GMX_RELEASE_ASSERT(a <= b, "The uniform integer distribution requires a<=b");
102 /*! \brief Return lower range */
103 result_type a() const { return a_; }
104 /*! \brief Return upper range */
105 result_type b() const { return b_; }
107 /*! \brief True if two parameter sets will return the same uniform int distribution.
109 * \param x Instance to compare with.
111 bool operator==(const param_type& x) const
113 // rangeBits is a function of a & b, so it does not have to be tested
114 return a_ == x.a_ && b_ == x.b_;
117 /*! \brief True if two parameter sets will return different uniform int distributions
119 * \param x Instance to compare with.
121 bool operator!=(const param_type& x) const { return !operator==(x); }
125 /*! \brief Construct new distribution with given integer parameters.
127 * \param a Lower end of range (inclusive)
128 * \param b Upper end of range (inclusive)
130 explicit UniformIntDistribution(result_type a = 0,
131 result_type b = std::numeric_limits<result_type>::max()) :
132 param_(param_type(a, b)),
134 savedRandomBitsLeft_(0)
138 /*! \brief Construct new distribution from parameter class
140 * \param param Parameter class as defined inside gmx::UniformIntDistribution.
142 explicit UniformIntDistribution(const param_type& param) :
145 savedRandomBitsLeft_(0)
149 /*! \brief Flush all internal saved values */
150 void reset() { savedRandomBitsLeft_ = 0; }
152 /*! \brief Return values from uniform int distribution with internal parameters
154 * \tparam Rng Uniform random engine class
156 * \param g Random engine
159 result_type operator()(Rng& g)
161 return (*this)(g, param_);
164 /*! \brief Return value from uniform int distribution with given parameters
166 * \tparam Rng Uniform random engine class
168 * \param g Random engine
169 * \param param Parameters to use
172 result_type operator()(Rng& g, const param_type& param)
174 static_assert(sizeof(typename Rng::result_type) >= sizeof(uint32_t),
175 "The random engine result_type should be 32 or 64 bits");
177 result_type range = param.b() - param.a();
178 unsigned int rangeBits;
185 else if (range == std::numeric_limits<result_type>::max())
187 rangeBits = std::numeric_limits<result_type>::digits; // Use all bits in type
191 if (sizeof(result_type) == sizeof(uint32_t))
193 rangeBits = log2I(static_cast<uint32_t>(range));
197 rangeBits = log2I(range);
199 rangeBits += ((range >> rangeBits) > 0);
204 if (savedRandomBitsLeft_ < rangeBits)
206 savedRandomBits_ = static_cast<uint64_t>(g());
207 savedRandomBitsLeft_ = std::numeric_limits<typename Rng::result_type>::digits;
209 if (sizeof(typename Rng::result_type) == sizeof(uint32_t))
211 savedRandomBits_ <<= std::numeric_limits<uint32_t>::digits;
212 savedRandomBits_ |= g();
213 savedRandomBitsLeft_ += std::numeric_limits<uint32_t>::digits;
216 result = savedRandomBits_;
217 savedRandomBits_ >>= rangeBits;
218 result = result - (savedRandomBits_ << rangeBits);
219 savedRandomBitsLeft_ -= rangeBits;
220 } while (result > range);
222 return result + param.a();
225 /*! \brief Return the lower range uniform int distribution */
226 result_type a() const { return param_.a(); }
228 /*! \brief Return the upper range of the uniform int distribution */
229 result_type b() const { return param_.b(); }
231 /*! \brief Return the full parameter class of the uniform int distribution */
232 param_type param() const { return param_; }
234 /*! \brief Smallest value that can be returned from uniform int distribution */
235 result_type min() const { return a(); }
237 /*! \brief Largest value that can be returned from uniform int distribution */
238 result_type max() const { return b(); }
240 /*! \brief True if two uniform int distributions will produce the same values.
242 * \param x Instance to compare with.
244 bool operator==(const UniformIntDistribution& x) const { return param_ == x.param_; }
246 /*! \brief True if two uniform int distributions will produce different values.
248 * \param x Instance to compare with.
250 bool operator!=(const UniformIntDistribution& x) const { return !operator==(x); }
253 /*! \brief Internal value for parameters, can be overridden at generation time. */
255 /*! \brief Saved output from random engine, shifted tableBits right each time */
256 uint64_t savedRandomBits_;
257 /*! \brief Number of valid bits remaining i savedRandomBits_ */
258 unsigned int savedRandomBitsLeft_;
260 GMX_DISALLOW_COPY_AND_ASSIGN(UniformIntDistribution);
265 #endif // GMX_RANDOM_UNIFORMINTDISTRIBUTION_H