code: private static long divide(final long dividend, final long divisor) {
          if (divisor < 0) { // i.e., divisor >= 2^63:
              if (compare(dividend, divisor) < 0) {
                  return 0; // dividend < divisor
              } else {
                  return 1; // dividend >= divisor
              }
          }
  
          // Optimization - use signed division if dividend < 2^63
          if (dividend >= 0) {
              return dividend / divisor;
          }
  
  
          // Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
          // guaranteed to be either exact or one less than the correct value. This follows from fact that
          // floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not quite
          // trivial.
          long quotient = ((dividend >>> 1) / divisor) << 1;
          long rem = dividend - quotient * divisor;
          return quotient + (compare(rem, divisor) >= 0 ? 1 : 0);
      }
docs: Returns dividend / divisor, where the dividend and divisor are treated as unsigned 64-bit quantities.