view libtommath/bn_mp_sqrt.c @ 487:2e17f82a7330

Add multihop 'onion-forwarding' mode. Needs refinement, works.
author Matt Johnston Thu, 18 Sep 2008 14:47:02 +0000 5ff8218bcee9 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
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], 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 \$ */