Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

82 lines (70 sloc) 1.77 kb
#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
/* $Source$ */
/* $Revision$ */
/* $Date$ */
Jump to Line
Something went wrong with that request. Please try again.