3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
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.
12 * The library is free for all purposes without any express
15 * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
18 /* low level addition, based on HAC pp.594, Algorithm 14.7 */
20 s_mp_add (mp_int * a, mp_int * b, mp_int * c)
23 int olduse, res, min, max;
25 /* find sizes, we let |a| <= |b| which means we have to sort
26 * them. "x" will point to the input with the most digits
28 if (a->used > b->used) {
39 if (c->alloc < max + 1) {
40 if ((res = mp_grow (c, max + 1)) != MP_OKAY) {
45 /* get old used digit count and set new one */
50 register mp_digit u, *tmpa, *tmpb, *tmpc;
53 /* alias for digit pointers */
66 for (i = 0; i < min; i++) {
67 /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
68 *tmpc = *tmpa++ + *tmpb++ + u;
70 /* U = carry bit of T[i] */
71 u = *tmpc >> ((mp_digit)DIGIT_BIT);
73 /* take away carry bit from T[i] */
77 /* now copy higher words if any, that is in A+B
78 * if A or B has more digits add those in
81 for (; i < max; i++) {
85 /* U = carry bit of T[i] */
86 u = *tmpc >> ((mp_digit)DIGIT_BIT);
88 /* take away carry bit from T[i] */
96 /* clear digits above oldused */
97 for (i = c->used; i < olduse; i++) {
107 /* $Source: /cvs/libtom/libtommath/bn_s_mp_add.c,v $ */
108 /* $Revision: 1.3 $ */
109 /* $Date: 2006/03/31 14:18:44 $ */