1 files changed, 53 insertions, 0 deletions
diff --git a/libtommath/bn_mp_expt_d.c b/libtommath/bn_mp_expt_d.c
new file mode 100644
index 0000000..fdb8bd9
--- /dev/null
+++ b/libtommath/bn_mp_expt_d.c
@@ -0,0 +1,53 @@
+#include <tommath.h>
+#ifdef BN_MP_EXPT_D_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
+ */
+
+/* calculate c = a**b  using a square-multiply algorithm */
+int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
+{
+  int     res, x;
+  mp_int  g;
+
+  if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
+    return res;
+  }
+
+  /* set initial result */
+  mp_set (c, 1);
+
+  for (x = 0; x < (int) DIGIT_BIT; x++) {
+    /* square */
+    if ((res = mp_sqr (c, c)) != MP_OKAY) {
+      mp_clear (&g);
+      return res;
+    }
+
+    /* if the bit is set multiply */
+    if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
+      if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
+         mp_clear (&g);
+         return res;
+      }
+    }
+
+    /* shift to next bit */
+    b <<= 1;
+  }
+
+  mp_clear (&g);
+  return MP_OKAY;
+}
+#endif