Mercurial > dropbear

comparison libtommath/bn_mp_sqrt.c @ 284:eed26cff980b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
parents
children 5ff8218bcee9
comparison
equal deleted inserted replaced
283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_SQRT_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* this function is less generic than mp_n_root, simpler and faster */
19 int mp_sqrt(mp_int *arg, mp_int *ret)
20 {
21 int res;
22 mp_int t1,t2;
23
24 /* must be positive */
25 if (arg->sign == MP_NEG) {
26 return MP_VAL;
27 }
28
29 /* easy out */
30 if (mp_iszero(arg) == MP_YES) {
31 mp_zero(ret);
32 return MP_OKAY;
33 }
34
35 if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
36 return res;
37 }
38
39 if ((res = mp_init(&t2)) != MP_OKAY) {
40 goto E2;
41 }
42
43 /* First approx. (not very bad for large arg) */
44 mp_rshd (&t1,t1.used/2);
45
46 /* t1 > 0 */
47 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
48 goto E1;
49 }
50 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
51 goto E1;
52 }
53 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
54 goto E1;
55 }
56 /* And now t1 > sqrt(arg) */
57 do {
58 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
59 goto E1;
60 }
61 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
62 goto E1;
63 }
64 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
65 goto E1;
66 }
67 /* t1 >= sqrt(arg) >= t2 at this point */
68 } while (mp_cmp_mag(&t1,&t2) == MP_GT);
69
70 mp_exch(&t1,ret);
71
72 E1: mp_clear(&t2);
73 E2: mp_clear(&t1);
74 return res;
75 }
76
77 #endif