kc3-lang/libtommath/mp_exteuclid.c

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• Hash : 1cc289d2
  Author :
  Date : 2019-11-09T20:23:03
  

  better use of mp_isneg() and mp_iszero()

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• mp_exteuclid.c

• #include "tommath_private.h"
  #ifdef MP_EXTEUCLID_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* Extended euclidean algorithm of (a, b) produces
     a*u1 + b*u2 = u3
   */
  mp_err mp_exteuclid(const mp_int *a, const mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
  {
     mp_int u1, u2, u3, v1, v2, v3, t1, t2, t3, q, tmp;
     mp_err 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) */
     mp_set(&u1, 1uL);
     if ((err = mp_copy(a, &u3)) != MP_OKAY)                        goto LBL_ERR;
  
     /* initialize, (v1,v2,v3) = (0,1,b) */
     mp_set(&v2, 1uL);
     if ((err = mp_copy(b, &v3)) != MP_OKAY)                        goto LBL_ERR;
  
     /* loop while v3 != 0 */
     while (!mp_iszero(&v3)) {
        /* q = u3/v3 */
        if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY)          goto LBL_ERR;
  
        /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
        if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY)               goto LBL_ERR;
        if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY)              goto LBL_ERR;
        if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY)               goto LBL_ERR;
        if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY)              goto LBL_ERR;
        if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY)               goto LBL_ERR;
        if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY)              goto LBL_ERR;
  
        /* (u1,u2,u3) = (v1,v2,v3) */
        if ((err = mp_copy(&v1, &u1)) != MP_OKAY)                   goto LBL_ERR;
        if ((err = mp_copy(&v2, &u2)) != MP_OKAY)                   goto LBL_ERR;
        if ((err = mp_copy(&v3, &u3)) != MP_OKAY)                   goto LBL_ERR;
  
        /* (v1,v2,v3) = (t1,t2,t3) */
        if ((err = mp_copy(&t1, &v1)) != MP_OKAY)                   goto LBL_ERR;
        if ((err = mp_copy(&t2, &v2)) != MP_OKAY)                   goto LBL_ERR;
        if ((err = mp_copy(&t3, &v3)) != MP_OKAY)                   goto LBL_ERR;
     }
  
     /* make sure U3 >= 0 */
     if (mp_isneg(&u3)) {
        if ((err = mp_neg(&u1, &u1)) != MP_OKAY)                    goto LBL_ERR;
        if ((err = mp_neg(&u2, &u2)) != MP_OKAY)                    goto LBL_ERR;
        if ((err = mp_neg(&u3, &u3)) != MP_OKAY)                    goto LBL_ERR;
     }
  
     /* copy result out */
     if (U1 != NULL) {
        mp_exch(U1, &u1);
     }
     if (U2 != NULL) {
        mp_exch(U2, &u2);
     }
     if (U3 != NULL) {
        mp_exch(U3, &u3);
     }
  
  LBL_ERR:
     mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
     return err;
  }
  #endif
  

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