Compute prime numbers
/* Compute prime numbers, after Knuth, Vol 1, Sec 1.3.2, Alg. "P".
* Unlike Knuth, I don't build table formatting into
* computational programs; output is one per line.
* <p>
* Note that there may be more efficient algorithms for finding primes.
* Consult a good book on numerical algorithms.
* @author Ian Darwin
*/
public class Primes {
/** The default stopping point for primes */
public static final long DEFAULT_STOP = 4294967295L;
/** The first prime number */
public static final int FP = 2;
static int MAX = 10000;
public static void main(String[] args) {
long[] prime = new long[MAX];
long stop = DEFAULT_STOP;
if (args.length == 1) {
stop = Long.parseLong(args[0]);
}
prime[1] = FP; // P1 (ignore prime[0])
long n = FP+1; // odd candidates
int j = 1; // numberFound
boolean isPrime = true; // for 3
do {
if (isPrime) {
if (j == MAX-1) {
// Grow array dynamically if needed
long[] np = new long[MAX * 2];
System.arraycopy(prime, 0, np, 0, MAX);
MAX *= 2;
prime = np;
}
prime[++j] = n; // P2
isPrime = false;
}
n += 2; // P4
for (int k = 2; k <= j && k < MAX; k++) { // P5, P6, P8
long q = n / prime[k];
long r = n % prime[k];
if (r == 0) {
break;
}
if (q <= prime[k]) { // P7
isPrime = true;
break;
}
}
} while (n < stop); // P3
for (int i=1; i<=j; i++)
System.out.println(prime[i]);
}
}
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