tommath/bn_mp_exteuclid.c

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#include "tommath_private.h"
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#ifdef BN_MP_EXTEUCLID_C
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/* 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.
*
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* SPDX-License-Identifier: Unlicense
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*/
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/* Extended euclidean algorithm of (a, b) produces
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a*u1 + b*u2 = u3
*/
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int mp_exteuclid(const mp_int *a, const mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
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{
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mp_int u1, u2, u3, v1, v2, v3, t1, t2, t3, q, tmp;
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int err;
if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
return err;
}
/* initialize, (u1,u2,u3) = (1,0,a) */
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mp_set(&u1, 1uL);
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if ((err = mp_copy(a, &u3)) != MP_OKAY) {
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goto LBL_ERR;
}
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/* initialize, (v1,v2,v3) = (0,1,b) */
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mp_set(&v2, 1uL);
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if ((err = mp_copy(b, &v3)) != MP_OKAY) {
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goto LBL_ERR;
}
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/* loop while v3 != 0 */
while (mp_iszero(&v3) == MP_NO) {
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/* q = u3/v3 */
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if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) {
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goto LBL_ERR;
}
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/* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
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if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) {
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goto LBL_ERR;
}
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/* (u1,u2,u3) = (v1,v2,v3) */
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if ((err = mp_copy(&v1, &u1)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_copy(&v2, &u2)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_copy(&v3, &u3)) != MP_OKAY) {
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goto LBL_ERR;
}
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/* (v1,v2,v3) = (t1,t2,t3) */
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if ((err = mp_copy(&t1, &v1)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_copy(&t2, &v2)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_copy(&t3, &v3)) != MP_OKAY) {
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goto LBL_ERR;
}
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}
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/* make sure U3 >= 0 */
if (u3.sign == MP_NEG) {
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if ((err = mp_neg(&u1, &u1)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_neg(&u2, &u2)) != MP_OKAY) {
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goto LBL_ERR;
}
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if ((err = mp_neg(&u3, &u3)) != MP_OKAY) {
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goto LBL_ERR;
}
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}
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/* copy result out */
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if (U1 != NULL) {
mp_exch(U1, &u1);
}
if (U2 != NULL) {
mp_exch(U2, &u2);
}
if (U3 != NULL) {
mp_exch(U3, &u3);
}
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err = MP_OKAY;
LBL_ERR:
mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
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return err;
}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */