1 files changed, 78 insertions, 0 deletions
diff --git a/bn_mp_mul_2.c b/bn_mp_mul_2.c
new file mode 100644
index 0000000..6936681
--- /dev/null
+++ b/bn_mp_mul_2.c
@@ -0,0 +1,78 @@
+#include <tommath.h>
+#ifdef BN_MP_MUL_2_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
+ */
+
+/* b = a*2 */
+int mp_mul_2(mp_int * a, mp_int * b)
+{
+  int     x, res, oldused;
+
+  /* grow to accomodate result */
+  if (b->alloc < a->used + 1) {
+    if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) {
+      return res;
+    }
+  }
+
+  oldused = b->used;
+  b->used = a->used;
+
+  {
+    register mp_digit r, rr, *tmpa, *tmpb;
+
+    /* alias for source */
+    tmpa = a->dp;
+    
+    /* alias for dest */
+    tmpb = b->dp;
+
+    /* carry */
+    r = 0;
+    for (x = 0; x < a->used; x++) {
+    
+      /* get what will be the *next* carry bit from the 
+       * MSB of the current digit 
+       */
+      rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1));
+      
+      /* now shift up this digit, add in the carry [from the previous] */
+      *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK;
+      
+      /* copy the carry that would be from the source 
+       * digit into the next iteration 
+       */
+      r = rr;
+    }
+
+    /* new leading digit? */
+    if (r != 0) {
+      /* add a MSB which is always 1 at this point */
+      *tmpb = 1;
+      ++(b->used);
+    }
+
+    /* now zero any excess digits on the destination 
+     * that we didn't write to 
+     */
+    tmpb = b->dp + b->used;
+    for (x = b->used; x < oldused; x++) {
+      *tmpb++ = 0;
+    }
+  }
+  b->sign = a->sign;
+  return MP_OKAY;
+}
+#endif