vpUniRand.cpp

/*
 * ViSP, open source Visual Servoing Platform software.
 * Copyright (C) 2005 - 2024 by Inria. All rights reserved.
 *
 * This software is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * See the file LICENSE.txt at the root directory of this source
 * distribution for additional information about the GNU GPL.
 *
 * For using ViSP with software that can not be combined with the GNU
 * GPL, please contact Inria about acquiring a ViSP Professional
 * Edition License.
 *
 * See https://visp.inria.fr for more information.
 *
 * This software was developed at:
 * Inria Rennes - Bretagne Atlantique
 * Campus Universitaire de Beaulieu
 * 35042 Rennes Cedex
 * France
 *
 * If you have questions regarding the use of this file, please contact
 * Inria at visp@inria.fr
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Description:
 * Pseudo random number generator.
 */
 
/*
 * PCG Random Number Generation for C.
 *
 * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * For additional information about the PCG random number generation scheme,
 * including its license and other licensing options, visit
 *
 *     http://www.pcg-random.org
 */
 
/*
 * This code is derived from the full C implementation, which is in turn
 * derived from the canonical C++ PCG implementation. The C++ version
 * has many additional features and is preferable if you can use C++ in
 * your project.
 */
 
// To ensure UINT32_MAX, INT32_MX are defined on centos, ubuntu 12.04 we define __STDC_LIMIT_MACROS
 
#define __STDC_LIMIT_MACROS
 
#include <stdint.h>
#include <visp3/core/vpUniRand.h>
 
BEGIN_VISP_NAMESPACE
vpUniRand::vpUniRand()
  : m_maxInvDbl(1.0 / static_cast<double>(UINT32_MAX)), m_maxInvFlt(1.0f / static_cast<float>(UINT32_MAX)), m_rng()
{ }

vpUniRand::vpUniRand(uint64_t seed, uint64_t seq)
  : m_maxInvDbl(1.0 / static_cast<double>(UINT32_MAX)), m_maxInvFlt(1.0f / static_cast<float>(UINT32_MAX)), m_rng()
{
  setSeed(seed, seq);
}

double vpUniRand::operator()() { return uniform(0.0, 1.0); }

uint32_t vpUniRand::boundedRand(uint32_t bound)
{
  // To avoid bias, we need to make the range of the RNG a multiple of
  // bound, which we do by dropping output less than a threshold.
  // A naive scheme to calculate the threshold would be to do
  //
  //     uint32_t threshold = 0x100000000ull % bound;
  //
  // but 64-bit div/mod is slower than 32-bit div/mod (especially on
  // 32-bit platforms).  In essence, we do
  //
  //     uint32_t threshold = (0x100000000ull-bound) % bound;
  //
  // because this version will calculate the same modulus, but the LHS
  // value is less than 2^32.
 
  uint32_t threshold = static_cast<uint64_t>(-static_cast<int64_t>(bound) % bound);
 
  // Uniformity guarantees that this loop will terminate.  In practice, it
  // should usually terminate quickly; on average (assuming all bounds are
  // equally likely), 82.25% of the time, we can expect it to require just
  // one iteration.  In the worst case, someone passes a bound of 2^31 + 1
  // (i.e., 2147483649), which invalidates almost 50% of the range.  In
  // practice, bounds are typically small and only a tiny amount of the range
  // is eliminated.
  for (;;) {
    uint32_t r = next();
    if (r >= threshold) {
      return r % bound;
    }
  }
}

uint32_t vpUniRand::next()
{
  const unsigned long long val_ll = 6364136223846793005ULL;
  const uint32_t val_31 = 31;
  uint64_t oldstate = m_rng.state;
  m_rng.state = (oldstate * val_ll) + m_rng.inc;
  uint32_t xorshifted = static_cast<uint32_t>(((oldstate >> 18u) ^ oldstate) >> 27u);
  uint32_t rot = oldstate >> 59u;
  return (xorshifted >> rot) | (xorshifted << (static_cast<uint32_t>((-static_cast<int64_t>(rot)) & val_31)));
}

int vpUniRand::uniform(int a, int b)
{
  if (a == b) {
    return a;
  }
  return boundedRand(b - a) + a;
}

float vpUniRand::uniform(float a, float b) { return (next() * m_maxInvFlt * (b - a)) + a; }

double vpUniRand::uniform(double a, double b) { return (next() * m_maxInvDbl * (b - a)) + a; }

void vpUniRand::setSeed(uint64_t initstate, uint64_t initseq)
{
  m_rng.state = 0U;
  m_rng.inc = (initseq << 1u) | 1u;
  next();
  m_rng.state += initstate;
  next();
}
 
 
std::vector<size_t> vpUniRand::sampleWithoutReplacement(size_t count, size_t vectorSize)
{
  count = std::min(count, vectorSize);
  std::vector<size_t> indices(count);
  size_t added = 0;
  for (size_t i = 0; i < vectorSize; ++i) {
    double randomVal = uniform(0.0, 1.0);
    if ((vectorSize - i) * randomVal < (count - added)) {
      indices[added++] = i;
    }
    if (added == count) {
      break;
    }
  }
  return indices;
}
 
END_VISP_NAMESPACE