esp8266_milight_hub/lib/Helpers/Units.h

#include <Arduino.h>
#include <inttypes.h>

#ifndef _UNITS_H
#define _UNITS_H

#define COLOR_TEMP_MAX_MIREDS 370
#define COLOR_TEMP_MIN_MIREDS 153

class Units {
public:
  template <typename T, typename V>
  static T rescale(T value, V newMax, float oldMax = 255.0) {
    return round(value * (newMax / oldMax));
  }

  static uint8_t miredsToBrightness(uint8_t mireds, uint8_t maxValue = 255) {
      // MiLight CCT bulbs range from 2700K-6500K, or ~370.3-153.8 mireds. Note
      // that mireds are inversely correlated with color temperature.
      uint32_t tempMireds = constrain(mireds, COLOR_TEMP_MIN_MIREDS, COLOR_TEMP_MAX_MIREDS);

      uint8_t scaledTemp = round(
        maxValue*
        (tempMireds - COLOR_TEMP_MIN_MIREDS)
          /
        static_cast<double>(COLOR_TEMP_MAX_MIREDS - COLOR_TEMP_MIN_MIREDS)
      );

      return (maxValue - scaledTemp);
  }

  static uint8_t brightnessToMireds(uint8_t value, uint8_t maxValue = 255) {
    uint8_t reverseValue = maxValue - value;
    uint8_t scaled = rescale(reverseValue, (COLOR_TEMP_MAX_MIREDS - COLOR_TEMP_MIN_MIREDS), maxValue);

    return COLOR_TEMP_MIN_MIREDS + scaled;
  }
};

#endif