2018-05-02 19:43:17 +00:00
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#include "tommath_private.h"
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2019-10-19 14:24:39 +00:00
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#ifdef MP_SQRT_C
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2019-04-07 13:29:11 +00:00
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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2004-04-11 20:46:22 +00:00
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/* this function is less generic than mp_n_root, simpler and faster */
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2019-05-12 22:22:18 +00:00
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mp_err mp_sqrt(const mp_int *arg, mp_int *ret)
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2004-04-11 20:46:22 +00:00
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{
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2019-05-19 15:16:13 +00:00
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mp_err err;
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2017-08-30 18:23:46 +00:00
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mp_int t1, t2;
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2004-04-11 20:46:22 +00:00
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2017-08-30 18:23:46 +00:00
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/* must be positive */
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if (arg->sign == MP_NEG) {
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return MP_VAL;
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}
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2004-04-11 20:46:22 +00:00
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2017-08-30 18:23:46 +00:00
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/* easy out */
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2019-04-09 09:08:26 +00:00
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if (MP_IS_ZERO(arg)) {
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2017-08-30 18:23:46 +00:00
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mp_zero(ret);
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return MP_OKAY;
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}
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2004-04-11 20:46:22 +00:00
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2019-05-19 15:16:13 +00:00
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if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) {
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return err;
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2017-08-30 18:23:46 +00:00
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}
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2004-04-11 20:46:22 +00:00
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2019-05-19 15:16:13 +00:00
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if ((err = mp_init(&t2)) != MP_OKAY) {
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2017-08-30 18:23:46 +00:00
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goto E2;
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}
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2004-04-11 20:46:22 +00:00
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2017-08-30 18:23:46 +00:00
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/* First approx. (not very bad for large arg) */
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mp_rshd(&t1, t1.used/2);
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2004-04-11 20:46:22 +00:00
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2017-08-30 18:23:46 +00:00
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/* t1 > 0 */
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2019-05-19 15:16:13 +00:00
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if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
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2004-04-11 20:46:22 +00:00
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goto E1;
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2017-08-30 18:23:46 +00:00
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}
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2019-05-19 15:16:13 +00:00
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if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
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2004-04-11 20:46:22 +00:00
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goto E1;
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2017-08-30 18:23:46 +00:00
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}
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2019-05-19 15:16:13 +00:00
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if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
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2004-04-11 20:46:22 +00:00
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goto E1;
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2017-08-30 18:23:46 +00:00
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}
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/* And now t1 > sqrt(arg) */
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do {
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2019-05-19 15:16:13 +00:00
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if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
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2017-08-30 18:23:46 +00:00
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goto E1;
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}
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2019-05-19 15:16:13 +00:00
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if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
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2017-08-30 18:23:46 +00:00
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goto E1;
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}
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2019-05-19 15:16:13 +00:00
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if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
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2017-08-30 18:23:46 +00:00
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goto E1;
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}
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/* t1 >= sqrt(arg) >= t2 at this point */
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} while (mp_cmp_mag(&t1, &t2) == MP_GT);
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2004-04-11 20:46:22 +00:00
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2017-08-30 18:23:46 +00:00
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mp_exch(&t1, ret);
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2004-04-11 20:46:22 +00:00
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2017-08-28 20:34:46 +00:00
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E1:
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2017-08-30 18:23:46 +00:00
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mp_clear(&t2);
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2017-08-28 20:34:46 +00:00
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E2:
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2017-08-30 18:23:46 +00:00
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mp_clear(&t1);
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2019-05-19 15:16:13 +00:00
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return err;
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2004-04-11 20:46:22 +00:00
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}
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2004-10-29 22:07:18 +00:00
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#endif
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