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