Rounding up and rounding down to the nearest order of base 10 magnitude.

OrderOfMagnitudeRounding.pde

// Some example code for rounding up and rounding down to the nearest order of base 10 magnitude.
// Thanks to this thread for pointing me in the right direction
// https://stackoverflow.com/questions/7906996/algorithm-to-round-to-the-next-order-of-magnitude-in-r


void setup() {
  int i = 1200;
  println("i = "+ i);
  println("---");
  println("log(i): "+log(i));  
  println("log10(i): " + log10(i));
  println("---");
  println("ceil(log10(i)): " + ceil(log10(i)));
  println("floor(log10(i)): " + floor(log10(i)));
  println("---");
  println("pow(10, ceil(log10(i))): " + pow(10, ceil(log10(i))));
  println("pow(10, floor(log10(i))): " + pow(10, floor(log10(i))));

  /*
   i = 1200
   ---
   log(i): 7.090077
   log10(i): 3.0791812
   ---
   ceil(log10(i)): 4
   floor(log10(i)): 3
   ---
   pow(10, ceil(log10(i))): 10000.0
   pow(10, floor(log10(i))): 1000.0
   */
}

// Calculates the base-10 logarithm of a number
float log10 (int x) {
  return (log(x) / log(10));
}