#include "tommath_private.h"
#ifdef MP_ADD_D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* single digit addition */
mp_err mp_add_d(const mp_int *a, mp_digit b, mp_int *c)
{
mp_err err;
int ix, oldused;
mp_digit *tmpa, *tmpc;
/* fast path for a == c */
if (a == c) {
if ((c->sign == MP_ZPOS) &&
!mp_iszero(c) &&
((c->dp[0] + b) < MP_DIGIT_MAX)) {
c->dp[0] += b;
return MP_OKAY;
}
if ((c->sign == MP_NEG) &&
(c->dp[0] > b)) {
c->dp[0] -= b;
return MP_OKAY;
}
}
/* grow c as required */
if (c->alloc < (a->used + 1)) {
if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
return err;
}
}
/* if a is negative and |a| >= b, call c = |a| - b */
if ((a->sign == MP_NEG) && ((a->used > 1) || (a->dp[0] >= b))) {
mp_int a_ = *a;
/* temporarily fix sign of a */
a_.sign = MP_ZPOS;
/* c = |a| - b */
err = mp_sub_d(&a_, b, c);
/* fix sign */
c->sign = MP_NEG;
/* clamp */
mp_clamp(c);
return err;
}
/* old number of used digits in c */
oldused = c->used;
/* source alias */
tmpa = a->dp;
/* destination alias */
tmpc = c->dp;
/* if a is positive */
if (a->sign == MP_ZPOS) {
/* add digits, mu is carry */
mp_digit mu = b;
for (ix = 0; ix < a->used; ix++) {
*tmpc = *tmpa++ + mu;
mu = *tmpc >> MP_DIGIT_BIT;
*tmpc++ &= MP_MASK;
}
/* set final carry */
ix++;
*tmpc++ = mu;
/* setup size */
c->used = a->used + 1;
} else {
/* a was negative and |a| < b */
c->used = 1;
/* the result is a single digit */
if (a->used == 1) {
*tmpc++ = b - a->dp[0];
} else {
*tmpc++ = b;
}
/* setup count so the clearing of oldused
* can fall through correctly
*/
ix = 1;
}
/* sign always positive */
c->sign = MP_ZPOS;
/* now zero to oldused */
MP_ZERO_DIGITS(tmpc, oldused - ix);
mp_clamp(c);
return MP_OKAY;
}
#endif
