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https://github.com/rn10950/RetroZilla.git
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115 lines
2.8 KiB
C
115 lines
2.8 KiB
C
/*
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* makeprime.c
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*
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* A simple prime generator function (and test driver). Prints out the
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* first prime it finds greater than or equal to the starting value.
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*
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* Usage: makeprime <start>
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include <stdio.h>
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#include <stdlib.h>
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#include <ctype.h>
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/* These two must be included for make_prime() to work */
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#include "mpi.h"
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#include "mpprime.h"
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/*
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make_prime(p, nr)
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Find the smallest prime integer greater than or equal to p, where
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primality is verified by 'nr' iterations of the Rabin-Miller
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probabilistic primality test. The caller is responsible for
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generating the initial value of p.
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Returns MP_OKAY if a prime has been generated, otherwise the error
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code indicates some other problem. The value of p is clobbered; the
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caller should keep a copy if the value is needed.
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*/
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mp_err make_prime(mp_int *p, int nr);
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/* The main() is not required -- it's just a test driver */
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int main(int argc, char *argv[])
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{
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mp_int start;
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mp_err res;
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if(argc < 2) {
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fprintf(stderr, "Usage: %s <start-value>\n", argv[0]);
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return 1;
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}
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mp_init(&start);
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if(argv[1][0] == '0' && tolower(argv[1][1]) == 'x') {
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mp_read_radix(&start, argv[1] + 2, 16);
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} else {
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mp_read_radix(&start, argv[1], 10);
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}
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mp_abs(&start, &start);
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if((res = make_prime(&start, 5)) != MP_OKAY) {
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fprintf(stderr, "%s: error: %s\n", argv[0], mp_strerror(res));
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mp_clear(&start);
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return 1;
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} else {
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char *buf = malloc(mp_radix_size(&start, 10));
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mp_todecimal(&start, buf);
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printf("%s\n", buf);
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free(buf);
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mp_clear(&start);
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return 0;
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}
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} /* end main() */
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/*------------------------------------------------------------------------*/
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mp_err make_prime(mp_int *p, int nr)
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{
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mp_err res;
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if(mp_iseven(p)) {
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mp_add_d(p, 1, p);
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}
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do {
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mp_digit which = prime_tab_size;
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/* First test for divisibility by a few small primes */
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if((res = mpp_divis_primes(p, &which)) == MP_YES)
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continue;
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else if(res != MP_NO)
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goto CLEANUP;
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/* If that passes, try one iteration of Fermat's test */
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if((res = mpp_fermat(p, 2)) == MP_NO)
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continue;
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else if(res != MP_YES)
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goto CLEANUP;
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/* If that passes, run Rabin-Miller as often as requested */
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if((res = mpp_pprime(p, nr)) == MP_YES)
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break;
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else if(res != MP_NO)
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goto CLEANUP;
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} while((res = mp_add_d(p, 2, p)) == MP_OKAY);
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CLEANUP:
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return res;
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} /* end make_prime() */
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/*------------------------------------------------------------------------*/
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/* HERE THERE BE DRAGONS */
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