68 lines
1.4 KiB
C
68 lines
1.4 KiB
C
#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
|