1 files changed, 105 insertions, 0 deletions
diff --git a/bn_s_mp_add.c b/bn_s_mp_add.c
new file mode 100644
index 0000000..2b378ae
--- /dev/null
+++ b/bn_s_mp_add.c
@@ -0,0 +1,105 @@
+#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