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/* shor.c: Implementation of Shor's factoring algorithm
Copyright 2003 Bjoern Butscher, Hendrik Weimer
This file is part of libquantum
libquantum is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3 of the License,
or (at your option) any later version.
libquantum is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with libquantum; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA
*/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <time.h>
#include <quantum.h>
int main(int argc, char **argv) {
quantum_reg qr;
int i;
int width, swidth;
int x = 0;
int N;
int c,q,a,b, factor;
srand(time(0));
if(argc == 1)
{
printf("Usage: shor [number]\n\n");
return 3;
}
N=atoi(argv[1]);
if(N<15)
{
printf("Invalid number\n\n");
return 3;
}
width=quantum_getwidth(N*N);
swidth=quantum_getwidth(N);
printf("N = %i, %i qubits required\n", N, width+3*swidth+2);
if(argc >= 3)
{
x = atoi(argv[2]);
}
while((quantum_gcd(N, x) > 1) || (x < 2))
{
x = rand() % N;
}
printf("Random seed: %i\n", x);
qr=quantum_new_qureg(0, width);
for(i=0;i<width;i++)
quantum_hadamard(i, &qr);
quantum_addscratch(3*swidth+2, &qr);
quantum_exp_mod_n(N, x, width, swidth, &qr);
for(i=0;i<3*swidth+2;i++)
{
quantum_bmeasure(0, &qr);
}
quantum_qft(width, &qr);
for(i=0; i<width/2; i++)
{
quantum_cnot(i, width-i-1, &qr);
quantum_cnot(width-i-1, i, &qr);
quantum_cnot(i, width-i-1, &qr);
}
c=quantum_measure(qr);
if(c==-1)
{
printf("Impossible Measurement!\n");
return 1;
}
if(c==0)
{
printf("Measured zero, try again.\n");
return 2;
}
q = 1<<(width);
printf("Measured %i (%f), ", c, (float)c/q);
quantum_frac_approx(&c, &q, width);
printf("fractional approximation is %i/%i.\n", c, q);
if((q % 2 == 1) && (2*q<(1<<width)))
{
printf("Odd denominator, trying to expand by 2.\n");
q *= 2;
}
if(q % 2 == 1)
{
printf("Odd period, try again.\n");
return 2;
}
printf("Possible period is %i.\n", q);
a = quantum_ipow(x, q/2) + 1 % N;
b = quantum_ipow(x, q/2) - 1 % N;
a = quantum_gcd(N, a);
b = quantum_gcd(N, b);
if(a>b)
factor=a;
else
factor=b;
if((factor < N) && (factor > 1))
{
printf("%i = %i * %i\n", N, factor, N/factor);
}
else
{
printf("Unable to determine factors, try again.\n");
return 2;
}
quantum_delete_qureg(&qr);
/* printf("Memory leak: %i bytes\n", (int) quantum_memman(0)); */
return 0;
}
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