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

   1 /*      $NetBSD: bn_mp_sub.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $ */
   2
   3 #include <tommath.h>
   4 #ifdef BN_MP_SUB_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 /* high level subtraction (handles signs) */
  21 int
  22 mp_sub (mp_int * a, mp_int * b, mp_int * c)
  23 {
  24   int     sa, sb, res;
  25
  26   sa = a->sign;
  27   sb = b->sign;
  28
  29   if (sa != sb) {
  30     /* subtract a negative from a positive, OR */
  31     /* subtract a positive from a negative. */
  32     /* In either case, ADD their magnitudes, */
  33     /* and use the sign of the first number. */
  34     c->sign = sa;
  35     res = s_mp_add (a, b, c);
  36   } else {
  37     /* subtract a positive from a positive, OR */
  38     /* subtract a negative from a negative. */
  39     /* First, take the difference between their */
  40     /* magnitudes, then... */
  41     if (mp_cmp_mag (a, b) != MP_LT) {
  42       /* Copy the sign from the first */
  43       c->sign = sa;
  44       /* The first has a larger or equal magnitude */
  45       res = s_mp_sub (a, b, c);
  46     } else {
  47       /* The result has the *opposite* sign from */
  48       /* the first number. */
  49       c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
  50       /* The second has a larger magnitude */
  51       res = s_mp_sub (b, a, c);
  52     }
  53   }
  54   return res;
  55 }
  56
  57 #endif
  58
  59 /* Source: /cvs/libtom/libtommath/bn_mp_sub.c,v  */
  60 /* Revision: 1.4  */
  61 /* Date: 2006/12/28 01:25:13  */