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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())
98 GMX_RELEASE_ASSERT(a <= b, "The uniform integer distribution requires a<=b");
101 /*! \brief Return lower range */
102 result_type a() const { return a_; }
103 /*! \brief Return upper range */
104 result_type b() const { return b_; }
106 /*! \brief True if two parameter sets will return the same uniform int distribution.
108 * \param x Instance to compare with.
111 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.
122 operator!=(const param_type &x) const { return !operator==(x); }
127 /*! \brief Construct new distribution with given integer parameters.
129 * \param a Lower end of range (inclusive)
130 * \param b Upper end of range (inclusive)
132 explicit UniformIntDistribution(result_type a = 0, result_type b = std::numeric_limits<result_type>::max())
133 : param_(param_type(a, b)), savedRandomBits_(0), savedRandomBitsLeft_(0) {}
135 /*! \brief Construct new distribution from parameter class
137 * \param param Parameter class as defined inside gmx::UniformIntDistribution.
139 explicit UniformIntDistribution(const param_type ¶m)
140 : param_(param), savedRandomBits_(0), savedRandomBitsLeft_(0) {}
142 /*! \brief Flush all internal saved values */
144 reset() { savedRandomBitsLeft_ = 0; }
146 /*! \brief Return values from uniform int distribution with internal parameters
148 * \tparam Rng Uniform random engine class
150 * \param g Random engine
154 operator()(Rng &g) { return (*this)(g, param_); }
156 /*! \brief Return value from uniform int distribution with given parameters
158 * \tparam Rng Uniform random engine class
160 * \param g Random engine
161 * \param param Parameters to use
165 operator()(Rng &g, const param_type ¶m)
167 static_assert(sizeof(typename Rng::result_type) >= sizeof(gmx_uint32_t),
168 "The random engine result_type should be 32 or 64 bits");
170 result_type range = param.b() - param.a();
171 unsigned int rangeBits;
178 else if (range == std::numeric_limits<result_type>::max())
180 rangeBits = std::numeric_limits<result_type>::digits; // Use all bits in type
184 if (sizeof(result_type) == sizeof(gmx_uint32_t))
186 rangeBits = log2I(static_cast<gmx_uint32_t>(range));
190 rangeBits = log2I(range);
192 rangeBits += ((range >> rangeBits) > 0);
197 if (savedRandomBitsLeft_ < rangeBits)
199 savedRandomBits_ = static_cast<gmx_uint64_t>(g());
200 savedRandomBitsLeft_ = std::numeric_limits<typename Rng::result_type>::digits;
202 if (sizeof(typename Rng::result_type) == sizeof(gmx_uint32_t))
204 savedRandomBits_ <<= std::numeric_limits<gmx_uint32_t>::digits;
205 savedRandomBits_ |= g();
206 savedRandomBitsLeft_ += std::numeric_limits<gmx_uint32_t>::digits;
209 result = savedRandomBits_;
210 savedRandomBits_ >>= rangeBits;
211 result = result - (savedRandomBits_ << rangeBits);
212 savedRandomBitsLeft_ -= rangeBits;
214 while (result > range);
216 return result + param.a();
219 /*! \brief Return the lower range uniform int distribution */
221 a() const { return param_.a(); }
223 /*! \brief Return the upper range of the uniform int distribution */
225 b() const { return param_.b(); }
227 /*! \brief Return the full parameter class of the uniform int distribution */
228 param_type param() const { return param_; }
230 /*! \brief Smallest value that can be returned from uniform int distribution */
232 min() const { return a(); }
234 /*! \brief Largest value that can be returned from uniform int distribution */
236 max() const { return b(); }
238 /*! \brief True if two uniform int distributions will produce the same values.
240 * \param x Instance to compare with.
243 operator==(const UniformIntDistribution &x) const
244 { return param_ == x.param_; }
246 /*! \brief True if two uniform int distributions will produce different values.
248 * \param x Instance to compare with.
251 operator!=(const UniformIntDistribution &x) const
252 { return !operator==(x); }
255 /*! \brief Internal value for parameters, can be overridden at generation time. */
257 /*! \brief Saved output from random engine, shifted tableBits right each time */
258 gmx_uint64_t savedRandomBits_;
259 /*! \brief Number of valid bits remaining i savedRandomBits_ */
260 unsigned int savedRandomBitsLeft_;
262 GMX_DISALLOW_COPY_AND_ASSIGN(UniformIntDistribution);
267 #endif // GMX_RANDOM_UNIFORMINTDISTRIBUTION_H