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comparison bn_mp_sqrt.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

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ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
parents
children d29b64170cf0
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-1:000000000000 2:86e0b50a9b58
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 *
3 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality.
5 *
6 * The library was designed directly after the MPI library by
7 * Michael Fromberger but has been written from scratch with
8 * additional optimizations in place.
9 *
10 * The library is free for all purposes without any express
11 * guarantee it works.
12 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */
15 #include <tommath.h>
16
17 /* this function is less generic than mp_n_root, simpler and faster */
18 int mp_sqrt(mp_int *arg, mp_int *ret)
19 {
20 int res;
21 mp_int t1,t2;
22
23 /* must be positive */
24 if (arg->sign == MP_NEG) {
25 return MP_VAL;
26 }
27
28 /* easy out */
29 if (mp_iszero(arg) == MP_YES) {
30 mp_zero(ret);
31 return MP_OKAY;
32 }
33
34 if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
35 return res;
36 }
37
38 if ((res = mp_init(&t2)) != MP_OKAY) {
39 goto E2;
40 }
41
42 /* First approx. (not very bad for large arg) */
43 mp_rshd (&t1,t1.used/2);
44
45 /* t1 > 0 */
46 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
47 goto E1;
48 }
49 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
50 goto E1;
51 }
52 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
53 goto E1;
54 }
55 /* And now t1 > sqrt(arg) */
56 do {
57 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
58 goto E1;
59 }
60 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
61 goto E1;
62 }
63 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
64 goto E1;
65 }
66 /* t1 >= sqrt(arg) >= t2 at this point */
67 } while (mp_cmp_mag(&t1,&t2) == MP_GT);
68
69 mp_exch(&t1,ret);
70
71 E1: mp_clear(&t2);
72 E2: mp_clear(&t1);
73 return res;
74 }
75