Using C function from Python ctypes

result.txt

$ gcc -shared -fPIC trial_division.c -o trial_division.so

$ time python uselib.py
14115591195084627607
14115591195084627607 = 3667917713 * 3848393639

real    0m30.045s
user    0m30.008s
sys     0m0.012s

trial_division.c

typedef unsigned long long ulonglong;

ulonglong trial_division(ulonglong n)
{
    ulonglong i;

    if (n % 2 == 0) return 2;
    if (n % 3 == 0) return 3;

    for (i=6; (i-1)*(i-1)<=n; i+=6) {
        if (n % (i-1) == 0) return (i-1);
        if (n % (i+1) == 0) return (i+1);
    }

    return 1;
}

uselib.py

from ctypes import *

n = 0xc3e4a76781a69e97

lib = CDLL('./trial_division.so')
lib.trial_division.argtypes = [c_ulonglong]
lib.trial_division.restype = c_ulonglong

p = lib.trial_division(n)
q = n // p
print n
print "%d = %d * %d" % (p*q, p, q)