Prime number calculator used as part of a debugging tutorial on talktotheduck.dev

PrimeMainMR.java

import java.math.BigInteger;

public class PrimeMainMR {
	public static int cnt = 0;

	// this is the RabinMiller test, deterministically correct for n < 341,550,071,728,321
	// http://rosettacode.org/wiki/Miller-Rabin_primality_test#Python:_Proved_correct_up_to_large_N
	public static boolean isPrime(BigInteger n, int precision) {

		if (n.compareTo(new BigInteger("341550071728321")) >= 0) {
			return n.isProbablePrime(precision);
		}

		int intN = n.intValue();
		if (intN == 1 || intN == 4 || intN == 6 || intN == 8) return false;
		if (intN == 2 || intN == 3 || intN == 5 || intN == 7) return true;

		int[] primesToTest = getPrimesToTest(n);
		if (n.equals(new BigInteger("3215031751"))) {
			return false;
		}
		BigInteger d = n.subtract(BigInteger.ONE);
		BigInteger s = BigInteger.ZERO;
		while (d.mod(BigInteger.valueOf(2)).equals(BigInteger.ZERO)) {
			d = d.shiftRight(1);
			s = s.add(BigInteger.ONE);
		}
		for (int a : primesToTest) {
			if (try_composite(a, d, n, s)) {
				return false;
			}
		}
		return true;
	}

	public static boolean isPrime(BigInteger n) {
		return isPrime(n, 100);
	}

	public static boolean isPrime(int n) {
		return isPrime(BigInteger.valueOf(n), 100);
	}

	public static boolean isPrime(long n) {
		return isPrime(BigInteger.valueOf(n), 100);
	}

	private static boolean try_composite(int a, BigInteger d, BigInteger n, BigInteger s) {
		BigInteger aB = BigInteger.valueOf(a);
		if (aB.modPow(d, n).equals(BigInteger.ONE)) {
			return false;
		}
		for (int i = 0; BigInteger.valueOf(i).compareTo(s) < 0; i++) {
			// if pow(a, 2**i * d, n) == n-1
			if (aB.modPow(BigInteger.valueOf(2).pow(i).multiply(d), n).equals(n.subtract(BigInteger.ONE))) {
				return false;
			}
		}
		return true;
	}

	private static int[] getPrimesToTest(BigInteger n) {
		if (n.compareTo(new BigInteger("3474749660383")) >= 0) {
			return new int[]{2, 3, 5, 7, 11, 13, 17};
		}
		if (n.compareTo(new BigInteger("2152302898747")) >= 0) {
			return new int[]{2, 3, 5, 7, 11, 13};
		}
		if (n.compareTo(new BigInteger("118670087467")) >= 0) {
			return new int[]{2, 3, 5, 7, 11};
		}
		if (n.compareTo(new BigInteger("25326001")) >= 0) {
			return new int[]{2, 3, 5, 7};
		}
		if (n.compareTo(new BigInteger("1373653")) >= 0) {
			return new int[]{2, 3, 5};
		}
		return new int[]{2, 3};
	}

	public static void main(String[] args) throws InterruptedException {
		for (int i = 2; i < Math.pow(10, 9); ++i) {
			if (isPrime(i)) {
				cnt++;
			}
			Thread.sleep(1);
		}
		System.out.println("Total number of primes: " + cnt);
	}

}