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comparison bn_mp_dr_is_modulus.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

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ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
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-1:000000000000 2:86e0b50a9b58
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 *
3 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality.
5 *
6 * The library was designed directly after the MPI library by
7 * Michael Fromberger but has been written from scratch with
8 * additional optimizations in place.
9 *
10 * The library is free for all purposes without any express
11 * guarantee it works.
12 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */
15 #include <tommath.h>
16
17 /* determines if a number is a valid DR modulus */
18 int mp_dr_is_modulus(mp_int *a)
19 {
20 int ix;
21
22 /* must be at least two digits */
23 if (a->used < 2) {
24 return 0;
25 }
26
27 /* must be of the form b**k - a [a <= b] so all
28 * but the first digit must be equal to -1 (mod b).
29 */
30 for (ix = 1; ix < a->used; ix++) {
31 if (a->dp[ix] != MP_MASK) {
32 return 0;
33 }
34 }
35 return 1;
36 }
37