Mercurial > dropbear

comparison libtommath/bn_mp_sqrt.c @ 302:973fccb59ea4 ucc-axis-hack

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propagate from branch 'au.asn.ucc.matt.dropbear' (head 11034278bd1917bebcbdc69cf53b1891ce9db121) to branch 'au.asn.ucc.matt.dropbear.ucc-axis-hack' (head 10a1f614fec73d0820c3f61160d9db409b9beb46)
author Matt Johnston <matt@ucc.asn.au>
date Sat, 25 Mar 2006 12:59:58 +0000
parents eed26cff980b
children 5ff8218bcee9
comparison
equal deleted inserted replaced
299:740e782679be 302:973fccb59ea4
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