release/src/router/dropbear/libtommath/bn_mp_add.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_ADD_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   4  *
   5  * LibTomMath is a library that provides multiple-precision
   6  * integer arithmetic as well as number theoretic functionality.
   7  *
   8  * The library was designed directly after the MPI library by
   9  * Michael Fromberger but has been written from scratch with
  10  * additional optimizations in place.
  11  *
  12  * The library is free for all purposes without any express
  13  * guarantee it works.
  14  *
  15  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
  16  */
  17
  18 /* high level addition (handles signs) */
  19 int mp_add (mp_int * a, mp_int * b, mp_int * c)
  20 {
  21   int     sa, sb, res;
  22
  23   /* get sign of both inputs */
  24   sa = a->sign;
  25   sb = b->sign;
  26
  27   /* handle two cases, not four */
  28   if (sa == sb) {
  29     /* both positive or both negative */
  30     /* add their magnitudes, copy the sign */
  31     c->sign = sa;
  32     res = s_mp_add (a, b, c);
  33   } else {
  34     /* one positive, the other negative */
  35     /* subtract the one with the greater magnitude from */
  36     /* the one of the lesser magnitude.  The result gets */
  37     /* the sign of the one with the greater magnitude. */
  38     if (mp_cmp_mag (a, b) == MP_LT) {
  39       c->sign = sb;
  40       res = s_mp_sub (b, a, c);
  41     } else {
  42       c->sign = sa;
  43       res = s_mp_sub (a, b, c);
  44     }
  45   }
  46   return res;
  47 }
  48
  49 #endif
  50
  51 /* $Source: /cvs/libtom/libtommath/bn_mp_add.c,v $ */
  52 /* $Revision: 1.3 $ */
  53 /* $Date: 2006/03/31 14:18:44 $ */