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#include "tommath_private.h"
#ifdef BN_S_MP_ADD_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* low level addition, based on HAC pp.594, Algorithm 14.7 */
mp_err s_mp_add(const mp_int *a, const mp_int *b, mp_int *c)
{
const mp_int *x;
mp_err err;
int olduse, 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 ((err = mp_grow(c, max + 1)) != MP_OKAY) {
return err;
}
}
/* 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)MP_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)MP_DIGIT_BIT;
/* take away carry bit from T[i] */
*tmpc++ &= MP_MASK;
}
}
/* add carry */
*tmpc++ = u;
/* clear digits above oldused */
MP_ZERO_DIGITS(tmpc, olduse - c->used);
}
mp_clamp(c);
return MP_OKAY;
}
#endif
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