summaryrefslogtreecommitdiffstats
path: root/libtommath/bn_mp_expt_d_ex.c
diff options
context:
space:
mode:
Diffstat (limited to 'libtommath/bn_mp_expt_d_ex.c')
-rw-r--r--libtommath/bn_mp_expt_d_ex.c83
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
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */