/* is the long prime by brute force */
static int isprime(long k)
{
long y, z;
y = i_sqrt(k);
for (z = 2; z <= y; z++) {
if ((k % z) == 0)
return 0;
}
return 1;
}
/* generates a prime digit */
static void gen_prime (void)
{
mp_digit r, x, y, next;
FILE *out;
out = fopen("pprime.dat", "wb");
/* write first set of primes */
r = 3; fwrite(&r, 1, sizeof(mp_digit), out);
r = 5; fwrite(&r, 1, sizeof(mp_digit), out);
r = 7; fwrite(&r, 1, sizeof(mp_digit), out);
r = 11; fwrite(&r, 1, sizeof(mp_digit), out);
r = 13; fwrite(&r, 1, sizeof(mp_digit), out);
r = 17; fwrite(&r, 1, sizeof(mp_digit), out);
r = 19; fwrite(&r, 1, sizeof(mp_digit), out);
r = 23; fwrite(&r, 1, sizeof(mp_digit), out);
r = 29; fwrite(&r, 1, sizeof(mp_digit), out);
r = 31; fwrite(&r, 1, sizeof(mp_digit), out);
/* get square root, since if 'r' is composite its factors must be < than this */
y = i_sqrt (r);
next = (y + 1) * (y + 1);
for (;;) {
do {
r += 2; /* next candidate */
r &= MP_MASK;
if (r < 31) break;
/* update sqrt ? */
if (next <= r) {
++y;
next = (y + 1) * (y + 1);
}
/* loop if divisible by 3,5,7,11,13,17,19,23,29 */
if ((r % 3) == 0) {
x = 0;
continue;
}
if ((r % 5) == 0) {
x = 0;
continue;
}
if ((r % 7) == 0) {
x = 0;
continue;
}
if ((r % 11) == 0) {
x = 0;
continue;
}
if ((r % 13) == 0) {
x = 0;
continue;
}
if ((r % 17) == 0) {
x = 0;
continue;
}
if ((r % 19) == 0) {
x = 0;
continue;
}
if ((r % 23) == 0) {
x = 0;
continue;
}
if ((r % 29) == 0) {
x = 0;
continue;
}
/* now check if r is divisible by x + k={1,7,11,13,17,19,23,29} */
for (x = 30; x <= y; x += 30) {
if ((r % (x + 1)) == 0) {
x = 0;
break;
}
if ((r % (x + 7)) == 0) {
x = 0;
break;
}
if ((r % (x + 11)) == 0) {
x = 0;
break;
}
if ((r % (x + 13)) == 0) {
x = 0;
break;
}
if ((r % (x + 17)) == 0) {
x = 0;
break;
}
if ((r % (x + 19)) == 0) {
x = 0;
break;
}
if ((r % (x + 23)) == 0) {
x = 0;
break;
}
if ((r % (x + 29)) == 0) {
x = 0;
break;
}
}
} while (x == 0);
if (r > 31) { fwrite(&r, 1, sizeof(mp_digit), out); printf("%9d\r", r); fflush(stdout); }
if (r < 31) break;
}
fclose(out);
}
