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https://github.com/libquantum/libquantum.git
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158 lines
3.0 KiB
C
158 lines
3.0 KiB
C
/* shor.c: Implementation of Shor's factoring algorithm
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Copyright 2003 Bjoern Butscher, Hendrik Weimer
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This file is part of libquantum
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libquantum is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published
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by the Free Software Foundation; either version 2 of the License,
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or (at your option) any later version.
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libquantum is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with libquantum; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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USA
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <math.h>
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#include <time.h>
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#include <quantum.h>
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int main(int argc, char **argv) {
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quantum_reg qr;
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int i;
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int width, swidth;
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int x = 0;
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int N;
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int c,q,a,b, factor;
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srandom(time(0));
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if(argc == 1)
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{
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printf("Usage: shor [number]\n\n");
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return 3;
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}
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N=atoi(argv[1]);
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if(N<15)
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{
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printf("Invalid number\n\n");
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return 3;
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}
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width=quantum_getwidth(N*N);
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swidth=quantum_getwidth(N);
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printf("N = %i, %i qubits required\n", N, width+3*swidth+2);
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if(argc >= 3)
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{
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x = atoi(argv[2]);
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}
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while((quantum_gcd(N, x) > 1) || (x < 2))
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{
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x = random() % N;
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}
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printf("Random seed: %i\n", x);
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qr=quantum_new_qureg(0, width);
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for(i=0;i<width;i++)
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quantum_hadamard(i, &qr);
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quantum_addscratch(3*swidth+2, &qr);
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quantum_exp_mod_n(N, x, width, swidth, &qr);
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for(i=0;i<3*swidth+2;i++)
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{
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quantum_bmeasure(0, &qr);
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}
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quantum_qft(width, &qr);
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for(i=0; i<width/2; i++)
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{
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quantum_cnot(i, width-i-1, &qr);
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quantum_cnot(width-i-1, i, &qr);
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quantum_cnot(i, width-i-1, &qr);
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}
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c=quantum_measure(qr);
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if(c==-1)
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{
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printf("Impossible Measurement!\n");
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exit(1);
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}
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if(c==0)
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{
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printf("Measured zero, try again.\n");
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exit(2);
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}
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q = 1<<(width);
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printf("Measured %i (%f), ", c, (float)c/q);
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quantum_frac_approx(&c, &q, width);
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printf("fractional approximation is %i/%i.\n", c, q);
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if((q % 2 == 1) && (2*q<(1<<width)))
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{
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printf("Odd denominator, trying to expand by 2.\n");
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q *= 2;
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}
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if(q % 2 == 1)
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{
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printf("Odd period, try again.\n");
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exit(2);
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}
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printf("Possible period is %i.\n", q);
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a = quantum_ipow(x, q/2) + 1 % N;
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b = quantum_ipow(x, q/2) - 1 % N;
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a = quantum_gcd(N, a);
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b = quantum_gcd(N, b);
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if(a>b)
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factor=a;
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else
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factor=b;
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if((factor < N) && (factor > 1))
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{
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printf("%i = %i * %i\n", N, factor, N/factor);
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}
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else
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{
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printf("Unable to determine factors, try again.\n");
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exit(2);
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}
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quantum_delete_qureg(&qr);
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/* printf("Memory leak: %i bytes\n", (int) quantum_memman(0)); */
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return 0;
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}
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