c3-lang/libtommath/bn_mp_exteuclid.c

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• Hash : 4e3f1344
  Author :
  Date : 2015-11-12T01:49:07
  

  provide tommath_private.h tommath.h contains declarations for the public part of the library. tommath_private.h contains the functions which are private to ltm and should not be exposed to the public.

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• bn_mp_exteuclid.c

• #include <tommath_private.h>
  #ifdef BN_MP_EXTEUCLID_C
  /* 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.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   *
   * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
   */
  
  /* Extended euclidean algorithm of (a, b) produces
     a*u1 + b*u2 = u3
   */
  int mp_exteuclid(mp_int *a, 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;
     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) */
     mp_set(&u1, 1);
     if ((err = mp_copy(a, &u3)) != MP_OKAY)                                        { goto _ERR; }
  
     /* initialize, (v1,v2,v3) = (0,1,b) */
     mp_set(&v2, 1);
     if ((err = mp_copy(b, &v3)) != MP_OKAY)                                        { goto _ERR; }
  
     /* loop while v3 != 0 */
     while (mp_iszero(&v3) == MP_NO) {
         /* q = u3/v3 */
         if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY)                         { goto _ERR; }
  
         /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
         if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
         if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY)                             { goto _ERR; }
         if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
         if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY)                             { goto _ERR; }
         if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
         if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY)                             { goto _ERR; }
  
         /* (u1,u2,u3) = (v1,v2,v3) */
         if ((err = mp_copy(&v1, &u1)) != MP_OKAY)                                  { goto _ERR; }
         if ((err = mp_copy(&v2, &u2)) != MP_OKAY)                                  { goto _ERR; }
         if ((err = mp_copy(&v3, &u3)) != MP_OKAY)                                  { goto _ERR; }
  
         /* (v1,v2,v3) = (t1,t2,t3) */
         if ((err = mp_copy(&t1, &v1)) != MP_OKAY)                                  { goto _ERR; }
         if ((err = mp_copy(&t2, &v2)) != MP_OKAY)                                  { goto _ERR; }
         if ((err = mp_copy(&t3, &v3)) != MP_OKAY)                                  { goto _ERR; }
     }
  
     /* make sure U3 >= 0 */
     if (u3.sign == MP_NEG) {
         if ((err = mp_neg(&u1, &u1)) != MP_OKAY)                                   { goto _ERR; }
         if ((err = mp_neg(&u2, &u2)) != MP_OKAY)                                   { goto _ERR; }
         if ((err = mp_neg(&u3, &u3)) != MP_OKAY)                                   { goto _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); }
  
     err = MP_OKAY;
  _ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
     return err;
  }
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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