1 /*	$NetBSD: bn_mp_div_2d.c,v 1.1.1.1 2011/04/13 18:14:54 elric 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) */
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