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/*
 * Testing how much a modulus operation can delay time based
 * operation of Arduino.
 * 
 * Modulus is slow, so including it in calculations using
 * millis() prior to setting your prevMillis = millis() for
 * incremental time keeping can slow things down
 * 
 * // The wrong way
 * something = (millis() - prevMillis) % something_else;
 * // long operation happend before we set prevMillis... DELAY
 * prevMillis = millis();
 
 * // The right way
 * increment = millis() - prevMillis;
 * prevMillis = millis();
 * // long operation happens after we have set prevMillis
 * something = increment % something_else;
 * 
 * The times I get in my code are:
 *  with % operation: 1332ms
 *  sans % operation: 165ms
 */
 
unsigned long int millisSinceStart = 0;
unsigned long int prevMillis = 0;
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  
  unsigned long int start = millis();
  unsigned long int finish;
  
  // Caculate how many milliseconds since Arduino was reset
  // rolling over every 24 hours (used in clock program)
  for (int i = 0 ; i < 32000 ; i++ ) {  
    millisSinceStart = 
      (millisSinceStart + millis() - prevMillis) % 86400000;
    prevMillis = millis();
  }
  finish = millis();
 
  
  Serial.print("Calculation with % operation: ");
  Serial.println(finish - start);
 
  // Same without modulus operation (no rollover - will last
  // for 49.5 days then rollover to 0.
  start = millis();
 
  for (int i = 0 ; i < 32000 ; i++ ) {  
    millisSinceStart = 
      (millisSinceStart + millis() - prevMillis);
    prevMillis = millis();
  }
  finish = millis();
  
  Serial.print("Calculation sans % operation: ");
  Serial.println(finish - start);
}