merge trunkinitsubsystems

1 files changed, 83 insertions, 0 deletions

diff --git a/libtommath/bn_mp_expt_d_ex.c b/libtommath/bn_mp_expt_d_ex.c
new file mode 100644
index 0000000..649d224
--- /dev/null
+++ b/libtommath/bn_mp_expt_d_ex.c
@@ -0,0 +1,83 @@
+#include <tommath_private.h>
+#ifdef BN_MP_EXPT_D_EX_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, tstdenis82@gmail.com, http://libtom.org
+ */
+
+/* calculate c = a**b  using a square-multiply algorithm */
+int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast)
+{
+  int     res;
+  unsigned int x;
+
+  mp_int  g;
+
+  if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
+    return res;
+  }
+
+  /* set initial result */
+  mp_set (c, 1);
+
+  if (fast != 0) {
+    while (b > 0) {
+      /* if the bit is set multiply */
+      if ((b & 1) != 0) {
+        if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
+          mp_clear (&g);
+          return res;
+        }
+      }
+
+      /* square */
+      if (b > 1) {
+        if ((res = mp_sqr (&g, &g)) != MP_OKAY) {
+          mp_clear (&g);
+          return res;
+        }
+      }
+
+      /* shift to next bit */
+      b >>= 1;
+    }
+  }
+  else {
+    for (x = 0; x < 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;
+    }
+  } /* if ... else */
+
+  mp_clear (&g);
+  return MP_OKAY;
+}
+#endif
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */