Visual Servoing Platform  version 3.4.1 under development (2021-04-20)
vpUniRand.cpp
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30  *
31  * Description:
32  * Pseudo random number generator.
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34  *****************************************************************************/
35  /*
36  * PCG Random Number Generation for C.
37  *
38  * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
39  *
40  * Licensed under the Apache License, Version 2.0 (the "License");
41  * you may not use this file except in compliance with the License.
42  * You may obtain a copy of the License at
43  *
44  * http://www.apache.org/licenses/LICENSE-2.0
45  *
46  * Unless required by applicable law or agreed to in writing, software
47  * distributed under the License is distributed on an "AS IS" BASIS,
48  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
49  * See the License for the specific language governing permissions and
50  * limitations under the License.
51  *
52  * For additional information about the PCG random number generation scheme,
53  * including its license and other licensing options, visit
54  *
55  * http://www.pcg-random.org
56  */
57 
58  /*
59  * This code is derived from the full C implementation, which is in turn
60  * derived from the canonical C++ PCG implementation. The C++ version
61  * has many additional features and is preferable if you can use C++ in
62  * your project.
63  */
64 
65 // To ensure UINT32_MAX, INT32_MX are defined on centos, ubuntu 12.04 we define __STDC_LIMIT_MACROS
66 
67 #define __STDC_LIMIT_MACROS
68 
69 #include <stdint.h>
70 #include <visp3/core/vpUniRand.h>
71 
73  m_maxInvDbl(1.0 / static_cast<double>(UINT32_MAX)), m_maxInvFlt(1.0f / static_cast<float>(UINT32_MAX)), m_rng()
74 {
75 }
76 
85 vpUniRand::vpUniRand(uint64_t seed, uint64_t seq) :
86  m_maxInvDbl(1.0 / static_cast<double>(UINT32_MAX)), m_maxInvFlt(1.0f / static_cast<float>(UINT32_MAX)), m_rng()
87 {
88  setSeed(seed, seq);
89 }
90 
96 {
97  return uniform(0.0, 1.0);
98 }
99 
112 uint32_t vpUniRand::boundedRand(uint32_t bound)
113 {
114  // To avoid bias, we need to make the range of the RNG a multiple of
115  // bound, which we do by dropping output less than a threshold.
116  // A naive scheme to calculate the threshold would be to do
117  //
118  // uint32_t threshold = 0x100000000ull % bound;
119  //
120  // but 64-bit div/mod is slower than 32-bit div/mod (especially on
121  // 32-bit platforms). In essence, we do
122  //
123  // uint32_t threshold = (0x100000000ull-bound) % bound;
124  //
125  // because this version will calculate the same modulus, but the LHS
126  // value is less than 2^32.
127 
128  uint32_t threshold = -bound % bound;
129 
130  // Uniformity guarantees that this loop will terminate. In practice, it
131  // should usually terminate quickly; on average (assuming all bounds are
132  // equally likely), 82.25% of the time, we can expect it to require just
133  // one iteration. In the worst case, someone passes a bound of 2^31 + 1
134  // (i.e., 2147483649), which invalidates almost 50% of the range. In
135  // practice, bounds are typically small and only a tiny amount of the range
136  // is eliminated.
137  for (;;) {
138  uint32_t r = next();
139  if (r >= threshold) {
140  return r % bound;
141  }
142  }
143 }
144 
149 uint32_t vpUniRand::next()
150 {
151  uint64_t oldstate = m_rng.state;
152  m_rng.state = oldstate * 6364136223846793005ULL + m_rng.inc;
153  uint32_t xorshifted = static_cast<uint32_t>(((oldstate >> 18u) ^ oldstate) >> 27u);
154  uint32_t rot = oldstate >> 59u;
155  return (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
156 }
157 
163 int vpUniRand::uniform(int a, int b)
164 {
165  if (a == b) {
166  return a;
167  }
168  return boundedRand(b - a) + a;
169 }
170 
176 float vpUniRand::uniform(float a, float b)
177 {
178  return next()*m_maxInvFlt*(b - a) + a;
179 }
180 
186 double vpUniRand::uniform(double a, double b)
187 {
188  return next()*m_maxInvDbl*(b - a) + a;
189 }
190 
212 void vpUniRand::setSeed(uint64_t initstate, uint64_t initseq)
213 {
214  m_rng.state = 0U;
215  m_rng.inc = (initseq << 1u) | 1u;
216  next();
217  m_rng.state += initstate;
218  next();
219 }
uint32_t next()
Definition: vpUniRand.cpp:149
void setSeed(uint64_t initstate, uint64_t initseq)
Definition: vpUniRand.cpp:212
int uniform(int a, int b)
Definition: vpUniRand.cpp:163
double operator()()
Definition: vpUniRand.cpp:95