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#include "tommath_private.h"
#ifdef BN_MP_SQRT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* this function is less generic than mp_n_root, simpler and faster */
mp_err mp_sqrt(const mp_int *arg, mp_int *ret)
{
mp_err err;
mp_int t1, t2;
/* must be positive */
if (arg->sign == MP_NEG) {
return MP_VAL;
}
/* easy out */
if (MP_IS_ZERO(arg)) {
mp_zero(ret);
return MP_OKAY;
}
if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) {
return err;
}
if ((err = mp_init(&t2)) != MP_OKAY) {
goto E2;
}
/* First approx. (not very bad for large arg) */
mp_rshd(&t1, t1.used/2);
/* t1 > 0 */
if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
goto E1;
}
if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
goto E1;
}
if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
goto E1;
}
/* And now t1 > sqrt(arg) */
do {
if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
goto E1;
}
if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
goto E1;
}
if ((err = 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 err;
}
#endif
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