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comparison libtommath/bn_mp_reduce_is_2k.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_REDUCE_IS_2K_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* determines if mp_reduce_2k can be used */
19 int mp_reduce_is_2k(mp_int *a)
20 {
21 int ix, iy, iw;
22 mp_digit iz;
23
24 if (a->used == 0) {
25 return MP_NO;
26 } else if (a->used == 1) {
27 return MP_YES;
28 } else if (a->used > 1) {
29 iy = mp_count_bits(a);
30 iz = 1;
31 iw = 1;
32
33 /* Test every bit from the second digit up, must be 1 */
34 for (ix = DIGIT_BIT; ix < iy; ix++) {
35 if ((a->dp[iw] & iz) == 0) {
36 return MP_NO;
37 }
38 iz <<= 1;
39 if (iz > (mp_digit)MP_MASK) {
40 ++iw;
41 iz = 1;
42 }
43 }
44 }
45 return MP_YES;
46 }
47
48 #endif