106 lines
2.4 KiB
C
106 lines
2.4 KiB
C
#include "tommath_private.h"
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#ifdef BN_S_MP_ADD_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* SPDX-License-Identifier: Unlicense
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*/
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/* low level addition, based on HAC pp.594, Algorithm 14.7 */
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int s_mp_add(const mp_int *a, const mp_int *b, mp_int *c)
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{
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const mp_int *x;
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int olduse, res, min, max;
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/* find sizes, we let |a| <= |b| which means we have to sort
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* them. "x" will point to the input with the most digits
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*/
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if (a->used > b->used) {
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min = b->used;
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max = a->used;
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x = a;
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} else {
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min = a->used;
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max = b->used;
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x = b;
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}
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/* init result */
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if (c->alloc < (max + 1)) {
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if ((res = mp_grow(c, max + 1)) != MP_OKAY) {
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return res;
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}
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}
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/* get old used digit count and set new one */
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olduse = c->used;
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c->used = max + 1;
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{
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mp_digit u, *tmpa, *tmpb, *tmpc;
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int i;
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/* alias for digit pointers */
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/* first input */
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tmpa = a->dp;
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/* second input */
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tmpb = b->dp;
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/* destination */
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tmpc = c->dp;
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/* zero the carry */
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u = 0;
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for (i = 0; i < min; i++) {
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/* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
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*tmpc = *tmpa++ + *tmpb++ + u;
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/* U = carry bit of T[i] */
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u = *tmpc >> (mp_digit)DIGIT_BIT;
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/* take away carry bit from T[i] */
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*tmpc++ &= MP_MASK;
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}
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/* now copy higher words if any, that is in A+B
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* if A or B has more digits add those in
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*/
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if (min != max) {
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for (; i < max; i++) {
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/* T[i] = X[i] + U */
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*tmpc = x->dp[i] + u;
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/* U = carry bit of T[i] */
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u = *tmpc >> (mp_digit)DIGIT_BIT;
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/* take away carry bit from T[i] */
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*tmpc++ &= MP_MASK;
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}
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}
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/* add carry */
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*tmpc++ = u;
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/* clear digits above oldused */
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for (i = c->used; i < olduse; i++) {
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*tmpc++ = 0;
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}
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}
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mp_clamp(c);
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return MP_OKAY;
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}
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#endif
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/* ref: $Format:%D$ */
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/* git commit: $Format:%H$ */
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/* commit time: $Format:%ai$ */
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