1 /*	$NetBSD: bn_mp_sqrt.c,v 1.1.1.1 2011/04/13 18:14:54 elric Exp $	*/
2 
3 #include <tommath.h>
4 #ifdef BN_MP_SQRT_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 /* this function is less generic than mp_n_root, simpler and faster */
21 int mp_sqrt(mp_int *arg, mp_int *ret)
22 {
23   int res;
24   mp_int t1,t2;
25 
26   /* must be positive */
27   if (arg->sign == MP_NEG) {
28     return MP_VAL;
29   }
30 
31   /* easy out */
32   if (mp_iszero(arg) == MP_YES) {
33     mp_zero(ret);
34     return MP_OKAY;
35   }
36 
37   if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
38     return res;
39   }
40 
41   if ((res = mp_init(&t2)) != MP_OKAY) {
42     goto E2;
43   }
44 
45   /* First approx. (not very bad for large arg) */
46   mp_rshd (&t1,t1.used/2);
47 
48   /* t1 > 0  */
49   if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
50     goto E1;
51   }
52   if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
53     goto E1;
54   }
55   if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
56     goto E1;
57   }
58   /* And now t1 > sqrt(arg) */
59   do {
60     if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
61       goto E1;
62     }
63     if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
64       goto E1;
65     }
66     if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
67       goto E1;
68     }
69     /* t1 >= sqrt(arg) >= t2 at this point */
70   } while (mp_cmp_mag(&t1,&t2) == MP_GT);
71 
72   mp_exch(&t1,ret);
73 
74 E1: mp_clear(&t2);
75 E2: mp_clear(&t1);
76   return res;
77 }
78 
79 #endif
80 
81 /* Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v */
82 /* Revision: 1.4 */
83 /* Date: 2006/12/28 01:25:13 */
84