int main(int args, char **argv) {
size_t bitset_size = 1 << (30 - 5);
uint64_t max_prime = bitset_size << 5;
fprintf(stderr, "Upper limit: %d\n", max_prime);
bitset bits;
bits.size = bitset_size;
bits.elements = calloc(sizeof(unsigned int), bits.size);
// Set all multiples of two to be non-primes and the rest
// to be primes
memset(bits.elements, 2 + 8 + 32 + 128, bits.size * sizeof(unsigned int));
bitset *primes = &bits;
bitset_unset(primes, 1);
bitset_set(primes, 2);
uint64_t p = 3;
while (p < max_prime) {
// Filter out all multiples of p
for (uint32_t i = p + p; i < max_prime; i += p) {
bitset_unset(primes, i);
}
// Find next number to filter out
do {
p += 2;
} while (p < max_prime && !bitset_isset(primes, p));
}
// Write to file
/*
FILE *fp = fopen("test2.raw", "w");
for (p = 2; p < max_prime; p++) {
if (bitset_isset(primes, p)) {
writeVarint64(p, fp);
}
}
fflush(fp);
fclose(fp);
fprintf(stderr, "wrote varints\n");
*/
FILE *fp = fopen("primes.bin", "w");
fwrite(bits.elements, sizeof(unsigned int), bits.size, fp);
fflush(fp);
fclose(fp);
fprintf(stderr, "Largest prime: %d\n", p - 2);
fprintf(stderr, "Wrote bitset: primes.bin\n");
free(bits.elements);
}
void char_bitset_unset(CharBitSet *b, unsigned char i)
{
bitset_unset((BitSet *)b, i);
}
