110 lines
2.3 KiB
C
110 lines
2.3 KiB
C
#include <tommath_private.h>
|
|
#ifdef BN_S_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, tstdenis82@gmail.com, http://libtom.org
|
|
*/
|
|
|
|
/* low level addition, based on HAC pp.594, Algorithm 14.7 */
|
|
int
|
|
s_mp_add (mp_int * a, mp_int * b, mp_int * c)
|
|
{
|
|
mp_int *x;
|
|
int olduse, res, min, max;
|
|
|
|
/* find sizes, we let |a| <= |b| which means we have to sort
|
|
* them. "x" will point to the input with the most digits
|
|
*/
|
|
if (a->used > b->used) {
|
|
min = b->used;
|
|
max = a->used;
|
|
x = a;
|
|
} else {
|
|
min = a->used;
|
|
max = b->used;
|
|
x = b;
|
|
}
|
|
|
|
/* init result */
|
|
if (c->alloc < (max + 1)) {
|
|
if ((res = mp_grow (c, max + 1)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
}
|
|
|
|
/* get old used digit count and set new one */
|
|
olduse = c->used;
|
|
c->used = max + 1;
|
|
|
|
{
|
|
mp_digit u, *tmpa, *tmpb, *tmpc;
|
|
int i;
|
|
|
|
/* alias for digit pointers */
|
|
|
|
/* first input */
|
|
tmpa = a->dp;
|
|
|
|
/* second input */
|
|
tmpb = b->dp;
|
|
|
|
/* destination */
|
|
tmpc = c->dp;
|
|
|
|
/* zero the carry */
|
|
u = 0;
|
|
for (i = 0; i < min; i++) {
|
|
/* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
|
|
*tmpc = *tmpa++ + *tmpb++ + u;
|
|
|
|
/* U = carry bit of T[i] */
|
|
u = *tmpc >> ((mp_digit)DIGIT_BIT);
|
|
|
|
/* take away carry bit from T[i] */
|
|
*tmpc++ &= MP_MASK;
|
|
}
|
|
|
|
/* now copy higher words if any, that is in A+B
|
|
* if A or B has more digits add those in
|
|
*/
|
|
if (min != max) {
|
|
for (; i < max; i++) {
|
|
/* T[i] = X[i] + U */
|
|
*tmpc = x->dp[i] + u;
|
|
|
|
/* U = carry bit of T[i] */
|
|
u = *tmpc >> ((mp_digit)DIGIT_BIT);
|
|
|
|
/* take away carry bit from T[i] */
|
|
*tmpc++ &= MP_MASK;
|
|
}
|
|
}
|
|
|
|
/* add carry */
|
|
*tmpc++ = u;
|
|
|
|
/* clear digits above oldused */
|
|
for (i = c->used; i < olduse; i++) {
|
|
*tmpc++ = 0;
|
|
}
|
|
}
|
|
|
|
mp_clamp (c);
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|
|
|
|
/* $Source$ */
|
|
/* $Revision$ */
|
|
/* $Date$ */
|