Upsilon/apps/shared/continuous_function_cache.cpp

#include "continuous_function_cache.h"
#include "continuous_function.h"
#include <limits.h>

namespace Shared {

constexpr int ContinuousFunctionCache::k_sizeOfCache;
constexpr float ContinuousFunctionCache::k_cacheHitTolerance;
constexpr int ContinuousFunctionCache::k_numberOfAvailableCaches;

// public
void ContinuousFunctionCache::PrepareForCaching(void * fun, ContinuousFunctionCache * cache, float tMin, float tStep) {
  ContinuousFunction * function = static_cast<ContinuousFunction *>(fun);

  if (!cache) {
    /* ContinuousFunctionStore::cacheAtIndex has returned a nullptr : the index
     * of the function we are trying to draw is greater than the number of
     * available caches, so we just tell the function to not lookup any cache. */
    function->setCache(nullptr);
    return;
  }

  if (tStep < 3 * k_cacheHitTolerance) {
    /* If tStep is lower than twice the tolerance, we risk shifting the index
     * by 1 for cache hits. As an added safety, we add another buffer of
     * k_cacheHitTolerance, raising the threshold for caching to three times
     * the tolerance. */
    function->setCache(nullptr);
    return;
  }
  if (function->cache() != cache) {
    cache->clear();
    function->setCache(cache);
  } else if (tStep != 0.f && tStep != cache->step()) {
    cache->clear();
  }

  if (function->plotType() == ContinuousFunction::PlotType::Cartesian && tStep != 0) {
    function->cache()->pan(function, tMin);
  }
  function->cache()->setRange(function, tMin, tStep);
}

void ContinuousFunctionCache::clear() {
  m_startOfCache = 0;
  m_tStep = 0;
  invalidateBetween(0, k_sizeOfCache);
}

Poincare::Coordinate2D<float> ContinuousFunctionCache::valueForParameter(const ContinuousFunction * function, Poincare::Context * context, float t) {
  int resIndex = indexForParameter(function, t);
  if (resIndex < 0) {
    return function->privateEvaluateXYAtParameter(t, context);
  }
  return valuesAtIndex(function, context, t, resIndex);
}

void ContinuousFunctionCache::ComputeNonCartesianSteps(float * tStep, float * tCacheStep, float tMax, float tMin) {
  // Expected step length
  *tStep = (tMax - tMin) / Graph::GraphView::k_graphStepDenominator;
  /* Parametric and polar functions require caching both x and y values,
   * with the same k_sizeOfCache. To cover the entire range,
   * number of cacheable points is half the cache size. */
  const int numberOfCacheablePoints = k_sizeOfCache / 2;
  const int numberOfWholeSteps = static_cast<int>(Graph::GraphView::k_graphStepDenominator);
  static_assert(numberOfCacheablePoints % numberOfWholeSteps == 0, "numberOfCacheablePoints should be a multiple of numberOfWholeSteps for optimal caching");
  const int multiple = numberOfCacheablePoints / numberOfWholeSteps;
  // Ignore this on Casio calculators for now, as the screen resolution breaks this
  // TODO: fix this. if it's possible
  #ifndef _FXCG
  static_assert(multiple && !(multiple & (multiple - 1)), "multiple should be a power of 2 for optimal caching");
  #endif
  /* Define cacheStep such that every whole graph steps are equally divided
   * For instance, with :
   *    graphStepDenominator = 10.1
   *    numberOfCacheablePoints = 160
   * tMin [----------------|----------------| ... |----------------|**] tMax
   *             step1           step2                  step10       step11
   * There are 11 steps, the first 10 are whole and have an equal size (tStep).
   * There are 16 cache points in the first 10 steps, 160 total cache points. */
  *tCacheStep = *tStep / multiple;
}

// private
void ContinuousFunctionCache::invalidateBetween(int iInf, int iSup) {
  for (int i = iInf; i < iSup; i++) {
    m_cache[i] = NAN;
  }
}

void ContinuousFunctionCache::setRange(ContinuousFunction * function, float tMin, float tStep) {
  m_tMin = tMin;
  m_tStep = tStep;
}

int ContinuousFunctionCache::indexForParameter(const ContinuousFunction * function, float t) const {
  float delta = (t - m_tMin) / m_tStep;
  if (delta < 0 || delta > INT_MAX) {
    return -1;
  }
  int res = std::round(delta);
  assert(res >= 0);
  if ((res >= k_sizeOfCache && function->plotType() == ContinuousFunction::PlotType::Cartesian)
   || (res >= k_sizeOfCache / 2 && function->plotType() != ContinuousFunction::PlotType::Cartesian)
   || std::fabs(res - delta) > k_cacheHitTolerance) {
    return -1;
  }
  assert(function->plotType() == ContinuousFunction::PlotType::Cartesian || m_startOfCache == 0);
  return (res + m_startOfCache) % k_sizeOfCache;
}

Poincare::Coordinate2D<float> ContinuousFunctionCache::valuesAtIndex(const ContinuousFunction * function, Poincare::Context * context, float t, int i) {
  if (function->plotType() == ContinuousFunction::PlotType::Cartesian) {
    if (std::isnan(m_cache[i])) {
      m_cache[i] = function->privateEvaluateXYAtParameter(t, context).x2();
    }
    return Poincare::Coordinate2D<float>(t, m_cache[i]);
  }
  if (std::isnan(m_cache[2 * i]) || std::isnan(m_cache[2 * i + 1])) {
    Poincare::Coordinate2D<float> res = function->privateEvaluateXYAtParameter(t, context);
    m_cache[2 * i] = res.x1();
    m_cache[2 * i + 1] = res.x2();
  }
  return Poincare::Coordinate2D<float>(m_cache[2 * i], m_cache[2 * i + 1]);
}

void ContinuousFunctionCache::pan(ContinuousFunction * function, float newTMin) {
  assert(function->plotType() == ContinuousFunction::PlotType::Cartesian);
  if (newTMin == m_tMin) {
    return;
  }

  float dT = (newTMin - m_tMin) / m_tStep;
  m_tMin = newTMin;
  if (std::fabs(dT) > INT_MAX) {
    clear();
    return;
  }
  int dI = std::round(dT);
  if (dI >= k_sizeOfCache || dI <= -k_sizeOfCache || std::fabs(dT - dI) > k_cacheHitTolerance) {
    clear();
    return;
  }

  int oldStart = m_startOfCache;
  m_startOfCache = (m_startOfCache + dI) % k_sizeOfCache;
  if (m_startOfCache < 0) {
    m_startOfCache += k_sizeOfCache;
  }
  if (dI > 0) {
    if (m_startOfCache > oldStart) {
      invalidateBetween(oldStart, m_startOfCache);
    } else {
      invalidateBetween(oldStart, k_sizeOfCache);
      invalidateBetween(0, m_startOfCache);
    }
  } else {
    if (m_startOfCache > oldStart) {
      invalidateBetween(m_startOfCache, k_sizeOfCache);
      invalidateBetween(0, oldStart);
    } else {
      invalidateBetween(m_startOfCache, oldStart);
    }
  }
}

}