1 /* $NetBSD: bn_mp_add.c,v 1.1.1.1 2011/04/13 18:14:54 elric Exp $ */ 2 3 #include <tommath.h> 4 #ifdef BN_MP_ADD_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 addition (handles signs) */ 21 int mp_add (mp_int * a, mp_int * b, mp_int * c) 22 { 23 int sa, sb, res; 24 25 /* get sign of both inputs */ 26 sa = a->sign; 27 sb = b->sign; 28 29 /* handle two cases, not four */ 30 if (sa == sb) { 31 /* both positive or both negative */ 32 /* add their magnitudes, copy the sign */ 33 c->sign = sa; 34 res = s_mp_add (a, b, c); 35 } else { 36 /* one positive, the other negative */ 37 /* subtract the one with the greater magnitude from */ 38 /* the one of the lesser magnitude. The result gets */ 39 /* the sign of the one with the greater magnitude. */ 40 if (mp_cmp_mag (a, b) == MP_LT) { 41 c->sign = sb; 42 res = s_mp_sub (b, a, c); 43 } else { 44 c->sign = sa; 45 res = s_mp_sub (a, b, c); 46 } 47 } 48 return res; 49 } 50 51 #endif 52 53 /* Source: /cvs/libtom/libtommath/bn_mp_add.c,v */ 54 /* Revision: 1.4 */ 55 /* Date: 2006/12/28 01:25:13 */ 56