1 /* $NetBSD: bn_mp_dr_is_modulus.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_DR_IS_MODULUS_C
5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20 /* determines if a number is a valid DR modulus */
mp_dr_is_modulus(mp_int * a)21 int mp_dr_is_modulus(mp_int *a)
22 {
23 int ix;
24
25 /* must be at least two digits */
26 if (a->used < 2) {
27 return 0;
28 }
29
30 /* must be of the form b**k - a [a <= b] so all
31 * but the first digit must be equal to -1 (mod b).
32 */
33 for (ix = 1; ix < a->used; ix++) {
34 if (a->dp[ix] != MP_MASK) {
35 return 0;
36 }
37 }
38 return 1;
39 }
40
41 #endif
42
43 /* Source: /cvs/libtom/libtommath/bn_mp_dr_is_modulus.c,v */
44 /* Revision: 1.4 */
45 /* Date: 2006/12/28 01:25:13 */
46