Fast sqrt in Java at the expense of accuracy

Question

I am looking for a fast square root implementation in Java for double values in the input range of [0, 2*10^12]. For any value in this range, the precision should be upto 5

Answer 1

Once you give the code time to warm up. Math.sqrt() can be pretty fast

static double[] values = new double[500 * 1000];

public static void main(String... args) {
    for (int i = 0; i < values.length; i++) values[i] = i;

    for (int j = 0; j < 5; j++) {
        long start = System.nanoTime();

        for (int i = 1; i < values.length; i++) {
            values[i] = Math.sqrt(values[i]);
        }
        long time = System.nanoTime() - start;

        System.out.printf("Took %d ns to Math.sqrt on average%n", time / values.length);
    }
}

prints

Took 20 ns to Math.sqrt on average
Took 22 ns to Math.sqrt on average
Took 9 ns to Math.sqrt on average
Took 9 ns to Math.sqrt on average
Took 9 ns to Math.sqrt on average