dither.cpp

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// Original version: Kevin Watts <watts@willowgarage.com>

#include <control_toolbox/dither.h>

#include <random>

namespace control_toolbox {

Dither::Dither() : amplitude_(0), has_saved_value_(false)
{

}

Dither::~Dither()
{
}

double Dither::update()
{
  if (has_saved_value_)
  {
    has_saved_value_ = false;
    return saved_value_;
  }

  // Generates gaussian random noise using the polar method.
  double v1, v2, r;
  // uniform distribution on the interval [-1.0, 1.0]
  std::uniform_real_distribution<double> distribution(-1.0, std::nextafter(1.0, std::numeric_limits<double>::max()));
  for (int i = 0; i < 100; ++i)
  {
    v1 = distribution(generator_);
    v2 = distribution(generator_);
    r = v1*v1 + v2*v2;
    if (r <= 1.0)
      break;
  }
  if (r > 1.0)
    r = 1.0;

  double f = sqrt(-2.0 * log(r) / r);
  double current = amplitude_ * f * v1;
  saved_value_ = amplitude_ * f * v2;
  has_saved_value_ = true;

  return current;
}

}