1 /* $NetBSD: bn_mp_mul_2d.c,v 1.2 2017/01/28 21:31:47 christos Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_MUL_2D_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 /* shift left by a certain bit count */
mp_mul_2d(mp_int * a,int b,mp_int * c)21 int mp_mul_2d (mp_int * a, int b, mp_int * c)
22 {
23 mp_digit d;
24 int res;
25
26 /* copy */
27 if (a != c) {
28 if ((res = mp_copy (a, c)) != MP_OKAY) {
29 return res;
30 }
31 }
32
33 if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
34 if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
35 return res;
36 }
37 }
38
39 /* shift by as many digits in the bit count */
40 if (b >= (int)DIGIT_BIT) {
41 if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
42 return res;
43 }
44 }
45
46 /* shift any bit count < DIGIT_BIT */
47 d = (mp_digit) (b % DIGIT_BIT);
48 if (d != 0) {
49 register mp_digit *tmpc, shift, mask, r, rr;
50 register int x;
51
52 /* bitmask for carries */
53 mask = (((mp_digit)1) << d) - 1;
54
55 /* shift for msbs */
56 shift = DIGIT_BIT - d;
57
58 /* alias */
59 tmpc = c->dp;
60
61 /* carry */
62 r = 0;
63 for (x = 0; x < c->used; x++) {
64 /* get the higher bits of the current word */
65 rr = (*tmpc >> shift) & mask;
66
67 /* shift the current word and OR in the carry */
68 *tmpc = ((*tmpc << d) | r) & MP_MASK;
69 ++tmpc;
70
71 /* set the carry to the carry bits of the current word */
72 r = rr;
73 }
74
75 /* set final carry */
76 if (r != 0) {
77 c->dp[(c->used)++] = r;
78 }
79 }
80 mp_clamp (c);
81 return MP_OKAY;
82 }
83 #endif
84
85 /* Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v */
86 /* Revision: 1.4 */
87 /* Date: 2006/12/28 01:25:13 */
88