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, tomstdenis (at) gmail.com, http://math.libtomcrypt.com 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 78 79 /* $Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v $ */ 80 /* $Revision: 1.3 $ */ 81 /* $Date: 2006/03/31 14:18:44 $ */ 82
