73 lines
2.6 KiB
C
73 lines
2.6 KiB
C
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#include "tommath_private.h"
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#ifdef MP_EXTEUCLID_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* Extended euclidean algorithm of (a, b) produces
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a*u1 + b*u2 = u3
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*/
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mp_err 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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mp_err err;
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if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
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return err;
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}
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/* 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) 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) goto LBL_ERR;
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/* loop while v3 != 0 */
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while (!mp_iszero(&v3)) {
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/* q = u3/v3 */
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if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) 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) goto LBL_ERR;
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if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) 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) goto LBL_ERR;
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if ((err = mp_copy(&v2, &u2)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_copy(&v3, &u3)) != MP_OKAY) 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) goto LBL_ERR;
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if ((err = mp_copy(&t2, &v2)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_copy(&t3, &v3)) != MP_OKAY) goto LBL_ERR;
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}
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/* make sure U3 >= 0 */
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if (mp_isneg(&u3)) {
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if ((err = mp_neg(&u1, &u1)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_neg(&u2, &u2)) != MP_OKAY) goto LBL_ERR;
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if ((err = mp_neg(&u3, &u3)) != MP_OKAY) goto LBL_ERR;
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}
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/* copy result out */
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if (U1 != NULL) {
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mp_exch(U1, &u1);
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}
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if (U2 != NULL) {
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mp_exch(U2, &u2);
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}
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if (U3 != NULL) {
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mp_exch(U3, &u3);
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}
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LBL_ERR:
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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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}
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#endif
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