Mercurial > dropbear
view libtommath/bn_mp_sqrt.c @ 607:aa2f51a6b81d DROPBEAR_0.53.1
Update changelog for 0.53.1
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 02 Mar 2011 13:23:27 +0000 (2011-03-02) |
parents | 5ff8218bcee9 |
children | 60fc6476e044 |
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#include <tommath.h> #ifdef BN_MP_SQRT_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com */ /* this function is less generic than mp_n_root, simpler and faster */ int mp_sqrt(mp_int *arg, mp_int *ret) { int res; mp_int t1,t2; /* must be positive */ if (arg->sign == MP_NEG) { return MP_VAL; } /* easy out */ if (mp_iszero(arg) == MP_YES) { mp_zero(ret); return MP_OKAY; } if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) { return res; } if ((res = mp_init(&t2)) != MP_OKAY) { goto E2; } /* First approx. (not very bad for large arg) */ mp_rshd (&t1,t1.used/2); /* t1 > 0 */ if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { goto E1; } if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { goto E1; } if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { goto E1; } /* And now t1 > sqrt(arg) */ do { if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { goto E1; } if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { goto E1; } if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { goto E1; } /* t1 >= sqrt(arg) >= t2 at this point */ } while (mp_cmp_mag(&t1,&t2) == MP_GT); mp_exch(&t1,ret); E1: mp_clear(&t2); E2: mp_clear(&t1); return res; } #endif /* $Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v $ */ /* $Revision: 1.3 $ */ /* $Date: 2006/03/31 14:18:44 $ */