1#include <tommath.h>
2#ifdef BN_MP_MOD_2D_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, tomstdenis@gmail.com, http://libtom.org
16 */
17
18/* calc a value mod 2**b */
19int
20mp_mod_2d (mp_int * a, int b, mp_int * c)
21{
22  int     x, res;
23
24  /* if b is <= 0 then zero the int */
25  if (b <= 0) {
26    mp_zero (c);
27    return MP_OKAY;
28  }
29
30  /* if the modulus is larger than the value than return */
31  if (b >= (int) (a->used * DIGIT_BIT)) {
32    res = mp_copy (a, c);
33    return res;
34  }
35
36  /* copy */
37  if ((res = mp_copy (a, c)) != MP_OKAY) {
38    return res;
39  }
40
41  /* zero digits above the last digit of the modulus */
42  for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
43    c->dp[x] = 0;
44  }
45  /* clear the digit that is not completely outside/inside the modulus */
46  c->dp[b / DIGIT_BIT] &=
47    (mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1));
48  mp_clamp (c);
49  return MP_OKAY;
50}
51#endif
52
53/* $Source$ */
54/* $Revision$ */
55/* $Date$ */
56