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#include "tommath_private.h"
#ifndef 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.
*
* SPDX-License-Identifier: Unlicense
*/
/* this function is less generic than mp_n_root, simpler and faster */
int mp_sqrt(const 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
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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