summaryrefslogtreecommitdiffstats
path: root/libtommath/bn_mp_expt_d_ex.c
blob: c361b27657bc64cdc92d87b41a9c9d7581a752ff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
#include <tommath_private.h>
#ifdef BN_MP_EXPT_D_EX_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
 */

/* calculate c = a**b  using a square-multiply algorithm */
int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast)
{
  int     res;
  unsigned int x;

  mp_int  g;

  if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
    return res;
  }

  /* set initial result */
  mp_set (c, 1);

  if (fast != 0) {
    while (b > 0) {
      /* if the bit is set multiply */
      if ((b & 1) != 0) {
        if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
          mp_clear (&g);
          return res;
        }
      }

      /* square */
      if (b > 1) {
        if ((res = mp_sqr (&g, &g)) != MP_OKAY) {
          mp_clear (&g);
          return res;
        }
      }

      /* shift to next bit */
      b >>= 1;
    }
  }
  else {
    for (x = 0; x < DIGIT_BIT; x++) {
      /* square */
      if ((res = mp_sqr (c, c)) != MP_OKAY) {
        mp_clear (&g);
        return res;
      }

      /* if the bit is set multiply */
      if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
        if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
           mp_clear (&g);
           return res;
        }
      }

      /* shift to next bit */
      b <<= 1;
    }
  } /* if ... else */

  mp_clear (&g);
  return MP_OKAY;
}
#endif

/* ref:         $Format:%D$ */
/* git commit:  $Format:%H$ */
/* commit time: $Format:%ai$ */