crypto/external/bsd/heimdal/dist/lib/hcrypto/libtommath/bn_mp_exteuclid.c

   1 /*      $NetBSD: bn_mp_exteuclid.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $   */
   2
   3 #include <tommath.h>
   4 #ifdef BN_MP_EXTEUCLID_C
   5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   6  *
   7  * LibTomMath is a library that provides multiple-precision
   8  * integer arithmetic as well as number theoretic functionality.
   9  *
  10  * The library was designed directly after the MPI library by
  11  * Michael Fromberger but has been written from scratch with
  12  * additional optimizations in place.
  13  *
  14  * The library is free for all purposes without any express
  15  * guarantee it works.
  16  *
  17  * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
  18  */
  19
  20 /* Extended euclidean algorithm of (a, b) produces
  21    a*u1 + b*u2 = u3
  22  */
  23 int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
  24 {
  25    mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp;
  26    int err;
  27
  28    if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
  29       return err;
  30    }
  31
  32    /* initialize, (u1,u2,u3) = (1,0,a) */
  33    mp_set(&u1, 1);
  34    if ((err = mp_copy(a, &u3)) != MP_OKAY)                                        { goto _ERR; }
  35
  36    /* initialize, (v1,v2,v3) = (0,1,b) */
  37    mp_set(&v2, 1);
  38    if ((err = mp_copy(b, &v3)) != MP_OKAY)                                        { goto _ERR; }
  39
  40    /* loop while v3 != 0 */
  41    while (mp_iszero(&v3) == MP_NO) {
  42        /* q = u3/v3 */
  43        if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY)                         { goto _ERR; }
  44
  45        /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
  46        if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
  47        if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY)                             { goto _ERR; }
  48        if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
  49        if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY)                             { goto _ERR; }
  50        if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
  51        if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY)                             { goto _ERR; }
  52
  53        /* (u1,u2,u3) = (v1,v2,v3) */
  54        if ((err = mp_copy(&v1, &u1)) != MP_OKAY)                                  { goto _ERR; }
  55        if ((err = mp_copy(&v2, &u2)) != MP_OKAY)                                  { goto _ERR; }
  56        if ((err = mp_copy(&v3, &u3)) != MP_OKAY)                                  { goto _ERR; }
  57
  58        /* (v1,v2,v3) = (t1,t2,t3) */
  59        if ((err = mp_copy(&t1, &v1)) != MP_OKAY)                                  { goto _ERR; }
  60        if ((err = mp_copy(&t2, &v2)) != MP_OKAY)                                  { goto _ERR; }
  61        if ((err = mp_copy(&t3, &v3)) != MP_OKAY)                                  { goto _ERR; }
  62    }
  63
  64    /* make sure U3 >= 0 */
  65    if (u3.sign == MP_NEG) {
  66       mp_neg(&u1, &u1);
  67       mp_neg(&u2, &u2);
  68       mp_neg(&u3, &u3);
  69    }
  70
  71    /* copy result out */
  72    if (U1 != NULL) { mp_exch(U1, &u1); }
  73    if (U2 != NULL) { mp_exch(U2, &u2); }
  74    if (U3 != NULL) { mp_exch(U3, &u3); }
  75
  76    err = MP_OKAY;
  77 _ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
  78    return err;
  79 }
  80 #endif
  81
  82 /* Source: /cvs/libtom/libtommath/bn_mp_exteuclid.c,v  */
  83 /* Revision: 1.4  */
  84 /* Date: 2006/12/28 01:25:13  */