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-rw-r--r--libtommath/bn_s_mp_add.c105
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+#include <tommath.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, tomstdenis@iahu.ca, http://math.libtomcrypt.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;
+
+ {
+ register mp_digit u, *tmpa, *tmpb, *tmpc;
+ register 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