1/*	$NetBSD$	*/
2
3#include <tommath.h>
4#ifdef BN_MP_REDUCE_2K_L_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/* reduces a modulo n where n is of the form 2**p - d
21   This differs from reduce_2k since "d" can be larger
22   than a single digit.
23*/
24int mp_reduce_2k_l(mp_int *a, mp_int *n, mp_int *d)
25{
26   mp_int q;
27   int    p, res;
28
29   if ((res = mp_init(&q)) != MP_OKAY) {
30      return res;
31   }
32
33   p = mp_count_bits(n);
34top:
35   /* q = a/2**p, a = a mod 2**p */
36   if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
37      goto ERR;
38   }
39
40   /* q = q * d */
41   if ((res = mp_mul(&q, d, &q)) != MP_OKAY) {
42      goto ERR;
43   }
44
45   /* a = a + q */
46   if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
47      goto ERR;
48   }
49
50   if (mp_cmp_mag(a, n) != MP_LT) {
51      s_mp_sub(a, n, a);
52      goto top;
53   }
54
55ERR:
56   mp_clear(&q);
57   return res;
58}
59
60#endif
61
62/* Source: /cvs/libtom/libtommath/bn_mp_reduce_2k_l.c,v */
63/* Revision: 1.4 */
64/* Date: 2006/12/28 01:25:13 */
65