1 /* $NetBSD: bn_mp_div_2d.c,v 1.2 2017/01/28 21:31:47 christos Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_DIV_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 right by a certain bit count (store quotient in c, optional remainder in d) */
mp_div_2d(mp_int * a,int b,mp_int * c,mp_int * d)21 int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
22 {
23 mp_digit D, r, rr;
24 int x, res;
25 mp_int t;
26
27
28 /* if the shift count is <= 0 then we do no work */
29 if (b <= 0) {
30 res = mp_copy (a, c);
31 if (d != NULL) {
32 mp_zero (d);
33 }
34 return res;
35 }
36
37 if ((res = mp_init (&t)) != MP_OKAY) {
38 return res;
39 }
40
41 /* get the remainder */
42 if (d != NULL) {
43 if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
44 mp_clear (&t);
45 return res;
46 }
47 }
48
49 /* copy */
50 if ((res = mp_copy (a, c)) != MP_OKAY) {
51 mp_clear (&t);
52 return res;
53 }
54
55 /* shift by as many digits in the bit count */
56 if (b >= (int)DIGIT_BIT) {
57 mp_rshd (c, b / DIGIT_BIT);
58 }
59
60 /* shift any bit count < DIGIT_BIT */
61 D = (mp_digit) (b % DIGIT_BIT);
62 if (D != 0) {
63 register mp_digit *tmpc, mask, shift;
64
65 /* mask */
66 mask = (((mp_digit)1) << D) - 1;
67
68 /* shift for lsb */
69 shift = DIGIT_BIT - D;
70
71 /* alias */
72 tmpc = c->dp + (c->used - 1);
73
74 /* carry */
75 r = 0;
76 for (x = c->used - 1; x >= 0; x--) {
77 /* get the lower bits of this word in a temp */
78 rr = *tmpc & mask;
79
80 /* shift the current word and mix in the carry bits from the previous word */
81 *tmpc = (*tmpc >> D) | (r << shift);
82 --tmpc;
83
84 /* set the carry to the carry bits of the current word found above */
85 r = rr;
86 }
87 }
88 mp_clamp (c);
89 if (d != NULL) {
90 mp_exch (&t, d);
91 }
92 mp_clear (&t);
93 return MP_OKAY;
94 }
95 #endif
96
97 /* Source: /cvs/libtom/libtommath/bn_mp_div_2d.c,v */
98 /* Revision: 1.4 */
99 /* Date: 2006/12/28 01:25:13 */
100