hexbright dot_product

int hexbright::dot_product(int* vector1, int* vector2) {
  // the max value sum could hit is technically > 2^16.
  //  However, the only instance where this is possible is if both vectors have
  //  experienced maximum acceleration on all axes - with 4 of the 6 being the max in the negative
  //  direction (-32 min, 31 max), (31*100/21.3) = 145, (-32*100/21.3) = -150
  //  3*(150^2) = 67500 (not safe)
  //  (150*150)+(150*150)+(145*145) = 66025 (not safe)
  //  (150*150)+(150*145)+(145*145) = 65275 (safe)
  //  3*(145^2) = 63075 (safe)
  // Given the difficulty of triggering this condition, I'm using an int.
  //  This could also be avoided by /100 inside the loop, costing 12 bytes.
  //  We should revisit this decision when drop detect code has been written.
  // An alternate solution would be to convert the sensor using READING*100/21.622,
  //  giving a max of 147.  3*(147^2) = 64827 (safe).  A max of 148 would be
  //  safe so long as no more than 5 values are -32.
  //  This would alter 1G to be 98 instead of 100, the closest values being 97(21) or 101(22).
  unsigned int sum = 0; // max value is about 3*(150^2), a tad over the maximum unsigned int
  for(int i=0;i<3;i++) {
    //sum+=vector1[i]*vector2[i]/100; // avoids overflow, but costs space
    sum+=vector1[i]*vector2[i];
  }
  return sum/100; // small danger of overflow
}