table2d.h

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/*
This file is used for everything related to maps/tables including their definition, functions etc
*/
#ifndef TABLE_H
#define TABLE_H
 
#include <stdint.h>
#include <Arduino.h>
 
// private to table2D implementation
 
namespace _table2d_detail {
 
// The 2D table cache
template <typename axis_t, typename value_t>
struct Table2DCache 
{
  // Store the upper index of the bin we last found. This is used to make the next check faster
  // Since this is the *upper* index, it can never be 0.
  uint8_t lastBinUpperIndex = 1U; // The axis bin search algo relies on this being 1 initially
 
  //Store the last input and output for caching
  axis_t lastInput = 0;
  value_t lastOutput = 0;
  uint8_t cacheTime = 0U; //Tracks when the last cache value was set so it can expire after x seconds. A timeout is required to pickup when a tuning value is changed, otherwise the old cached value will continue to be returned as the X value isn't changing. 
 
  constexpr Table2DCache(void) = default;
};
 
extern uint8_t getCacheTime(void);
 
template <typename axis_t, typename value_t>
static inline bool cacheExpired(const Table2DCache<axis_t, value_t> &cache) {
  return (cache.cacheTime != getCacheTime());
}
 
} // _table2d_detail
 
 
template <typename axis_t, typename value_t, uint8_t sizeT>
struct table2D
{
  using size_type = uint8_t;
 
  value_t (&values)[sizeT];
  axis_t (&axis)[sizeT];
 
  mutable _table2d_detail::Table2DCache<axis_t, value_t> cache;
 
  constexpr table2D(axis_t (*pAxisBin)[sizeT], value_t (*pCurve)[sizeT])
    : values(*pCurve) //cppcheck-suppress misra-c2012-10.4
    , axis(*pAxisBin) 
  {
  }
  
  static constexpr size_type size(void) { return sizeT; }  
};
 
 
// private to table2D implementation
 
namespace _table2d_detail {
 
template <typename T>
struct Bin {
  constexpr Bin(const T *array, uint8_t binUpperIndex)
  : upperIndex(binUpperIndex)
  , _upperValue(array[binUpperIndex])
  , _lowerValue(array[binUpperIndex-1U])
  {
  } 
  constexpr Bin(uint8_t binUpperIndex, const T upperValue, const T lowerValue)
  : upperIndex(binUpperIndex)
  , _upperValue(upperValue)
  , _lowerValue(lowerValue)
  {
  } 
 
  const T upperValue(void) const noexcept { return _upperValue; }
  const T lowerValue(void) const noexcept { return _lowerValue; }
 
  static bool withinBin(const T &value, const T &min, const T&max) noexcept {
    return (value <= max) && (value > min);
  }
  bool withinBin(const T value) const noexcept {
    return withinBin(value, lowerValue(), upperValue());
  }
 
  uint8_t upperIndex;
  T _upperValue;
  T _lowerValue;
};
 
 
template <typename T, uint8_t sizeT>
static inline Bin<T> findBin(const T *const array, const T value) 
{
  // Loop from the upper end of the axis back down to the 1st bin [0,1]
  // Assume array is ordered [min...max]
  const T *binLower = array+sizeT-2U;
  while ( (*binLower >= value) && (binLower != array) ) { --binLower; }
  return Bin<T>(binLower-array+1U, *(binLower+1U), *binLower);
}
 
// Generic interpolation
template <typename axis_t, typename value_t>
static inline value_t interpolate(const axis_t axisValue, const Bin<axis_t> &axisBin, const Bin<value_t> &valueBin) 
{
  return map(axisValue, axisBin.lowerValue(), axisBin.upperValue(), valueBin.lowerValue(), valueBin.upperValue());
}
 
// Specialized interpolation of uint8_t for performance
uint8_t interpolate(const uint8_t axisValue, const Bin<uint8_t> &axisBin, const Bin<uint8_t> &valueBin);
 
} // _table2d_detail
 
 
template <typename axis_t, typename value_t, uint8_t sizeT>
static inline value_t table2D_getValue(const table2D<axis_t, value_t, sizeT> *fromTable, const axis_t axisValue) 
{
  //Check whether the X input is the same as last time this ran
  if( (axisValue == fromTable->cache.lastInput) && (!cacheExpired(fromTable->cache)) ) { return fromTable->cache.lastOutput; }
  else if(axisValue >= fromTable->axis[sizeT-1]) // Test if above the max axis value, clip to max data value
  {
    fromTable->cache.lastOutput = fromTable->values[sizeT-1];
    fromTable->cache.lastBinUpperIndex = sizeT-1;
  } 
  else if (axisValue <= fromTable->axis[0]) // Test if below the min axis value, clip to min data value
  {
    fromTable->cache.lastOutput = fromTable->values[0];
    fromTable->cache.lastBinUpperIndex = 1U;
  } 
  else 
  {
    // None of the cached or last values match, so we need to find the new value
    // 1st check is whether we're still in the same X bin as last time
    _table2d_detail::Bin<axis_t> xBin = _table2d_detail::Bin<axis_t>(fromTable->axis, fromTable->cache.lastBinUpperIndex);
    if (!xBin.withinBin(axisValue))
    {
      //If we're not in the same bin, search 
      xBin = _table2d_detail::findBin<axis_t, sizeT>(fromTable->axis, axisValue);
    }
 
    // We are exactly at the bin upper bound, so no need to interpolate
    if (axisValue==xBin.upperValue()) 
    {
      fromTable->cache.lastOutput = fromTable->values[xBin.upperIndex];
      fromTable->cache.lastBinUpperIndex = xBin.upperIndex;
    } 
    else // Must be within the bin, interpolate
    {
      fromTable->cache.lastOutput = _table2d_detail::interpolate(axisValue, xBin, _table2d_detail::Bin<value_t>(fromTable->values, xBin.upperIndex));
      fromTable->cache.lastBinUpperIndex = xBin.upperIndex;
    }
    // Note: we cannot be at the bin lower bound here, as that would violate the bin definition of a non-inclusive lower bound
  }
  fromTable->cache.cacheTime = _table2d_detail::getCacheTime(); //As we're not using the cache value, set the current secl value to track when this new value was calculated
  fromTable->cache.lastInput = axisValue;
 
  return fromTable->cache.lastOutput;  
}
 
// Hide use of template in the header file
using table2D_i8_u8_4 = table2D<int8_t, uint8_t, 4U>;
using table2D_u8_u8_4 = table2D<uint8_t, uint8_t, 4U>;
using table2D_u8_u8_6 = table2D<uint8_t, uint8_t, 6U>;
using table2D_u8_u8_8 = table2D<uint8_t, uint8_t, 8U>;
using table2D_u8_u8_9 = table2D<uint8_t, uint8_t, 9U>;
using table2D_u8_u8_10 = table2D<uint8_t, uint8_t, 10U>;
using table2D_u16_u8_32 = table2D<uint16_t, uint8_t, 32U>;
using table2D_u16_u16_32 = table2D<uint16_t, uint16_t, 32U>;
using table2D_u8_u16_4 = table2D<uint8_t, uint16_t, 4U>;
using table2D_u8_s16_6 = table2D<uint8_t, int16_t, 6U>;
 
#endif // TABLE_H