Number factoring

gistfile1.cpp

#include <cstdio>
#include <ctime>
#include <cstring>
using namespace std;
const size_t s = 0x100;
const size_t ss = s * s;
size_t * p;
bool t[ss] = {};
void prepare() {
    for (size_t i = 2; i < s; ++i) if (!t[i]) for (size_t j = i * i; j < ss; j += i) t[j] = true;
    size_t k = 0;
    for (size_t i = 2; i < ss; ++i) if (!t[i]) ++k;
    p = new size_t[k];
    for (size_t i = 2, j = 0; i < ss; ++i) if (!t[i]) p[j++] = i;
}
void factor(size_t n) {
    size_t i = 0;
    size_t x = n;
    size_t j = 0;
    size_t f[0x40];
    for (;;) {
        size_t c = p[i];
        size_t d = x / c;
        size_t r = x % c;
        if (r) ++i;
        else {
            x = d;
            f[j++] = c;
            if (x == 1) break;
        }
    }
    size_t m = 1;
    for (size_t k = 0; k < j; ++k) m *= f[k];
    if (m != n) throw;
}
int main() {
    clock_t c1 = clock();
    prepare();
    for (size_t i = 2; i < ss; ++i) factor(i);
    clock_t c2 = clock();
    printf("%u\n", c2 - c1);
}