|
282
|
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 |
