| #include <tommath.h> |

| #ifdef BN_MP_ADD_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, tomstdenis@iahu.ca, http://math.libtomcrypt.org |

| */ |

| |

| /* high level addition (handles signs) */ |

| int mp_add (mp_int * a, mp_int * b, mp_int * c) |

| { |

| int sa, sb, res; |

| |

| /* get sign of both inputs */ |

| sa = a->sign; |

| sb = b->sign; |

| |

| /* handle two cases, not four */ |

| if (sa == sb) { |

| /* both positive or both negative */ |

| /* add their magnitudes, copy the sign */ |

| c->sign = sa; |

| res = s_mp_add (a, b, c); |

| } else { |

| /* one positive, the other negative */ |

| /* subtract the one with the greater magnitude from */ |

| /* the one of the lesser magnitude. The result gets */ |

| /* the sign of the one with the greater magnitude. */ |

| if (mp_cmp_mag (a, b) == MP_LT) { |

| c->sign = sb; |

| res = s_mp_sub (b, a, c); |

| } else { |

| c->sign = sa; |

| res = s_mp_sub (a, b, c); |

| } |

| } |

| return res; |

| } |

| |

| #endif |