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// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// * Neither the name of ETH Zurich and UNC Chapel Hill nor the names of
// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Author: Johannes L. Schoenberger (jsch-at-demuc-dot-de)
#ifndef COLMAP_SRC_UTIL_RANDOM_H_
#define COLMAP_SRC_UTIL_RANDOM_H_
#include <chrono>
#include <memory>
#include <random>
#include <thread>
#include "util/logging.h"
namespace colmap {
extern thread_local std::unique_ptr<std::mt19937> PRNG;
extern int kDefaultPRNGSeed;
// Initialize the PRNG with the given seed.
//
// @param seed The seed for the PRNG. If the seed is -1, the current time
// is used as the seed.
void SetPRNGSeed(unsigned seed = kDefaultPRNGSeed);
// Generate uniformly distributed random integer number.
//
// This implementation is unbiased and thread-safe in contrast to `rand()`.
template <typename T>
T RandomInteger(const T min, const T max);
// Generate uniformly distributed random real number.
//
// This implementation is unbiased and thread-safe in contrast to `rand()`.
template <typename T>
T RandomReal(const T min, const T max);
// Generate Gaussian distributed random real number.
//
// This implementation is unbiased and thread-safe in contrast to `rand()`.
template <typename T>
T RandomGaussian(const T mean, const T stddev);
// Fisher-Yates shuffling.
//
// Note that the vector may not contain more values than UINT32_MAX. This
// restriction comes from the fact that the 32-bit version of the
// Mersenne Twister PRNG is significantly faster.
//
// @param elems Vector of elements to shuffle.
// @param num_to_shuffle Optional parameter, specifying the number of first
// N elements in the vector to shuffle.
template <typename T>
void Shuffle(const uint32_t num_to_shuffle, std::vector<T>* elems);
////////////////////////////////////////////////////////////////////////////////
// Implementation
////////////////////////////////////////////////////////////////////////////////
template <typename T>
T RandomInteger(const T min, const T max) {
if (PRNG == nullptr) {
SetPRNGSeed();
}
std::uniform_int_distribution<T> distribution(min, max);
return distribution(*PRNG);
}
template <typename T>
T RandomReal(const T min, const T max) {
if (PRNG == nullptr) {
SetPRNGSeed();
}
std::uniform_real_distribution<T> distribution(min, max);
return distribution(*PRNG);
}
template <typename T>
T RandomGaussian(const T mean, const T stddev) {
if (PRNG == nullptr) {
SetPRNGSeed();
}
std::normal_distribution<T> distribution(mean, stddev);
return distribution(*PRNG);
}
template <typename T>
void Shuffle(const uint32_t num_to_shuffle, std::vector<T>* elems) {
CHECK_LE(num_to_shuffle, elems->size());
const uint32_t last_idx = static_cast<uint32_t>(elems->size() - 1);
for (uint32_t i = 0; i < num_to_shuffle; ++i) {
const auto j = RandomInteger<uint32_t>(i, last_idx);
std::swap((*elems)[i], (*elems)[j]);
}
}
} // namespace colmap
#endif // COLMAP_SRC_UTIL_RANDOM_H_
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