Libtommath 1.3

1 files changed, 53 insertions, 0 deletions

diff --git a/libtommath/bn_mp_expt_n.c b/libtommath/bn_mp_expt_n.c
new file mode 100644
index 0000000..19c0225
--- /dev/null
+++ b/libtommath/bn_mp_expt_n.c
@@ -0,0 +1,53 @@
+#include "tommath_private.h"
+#ifdef BN_MP_EXPT_N_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+#ifdef BN_MP_EXPT_U32_C
+mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c)
+{
+   if (b > MP_MIN(MP_DIGIT_MAX, INT_MAX)) {
+      return MP_VAL;
+   }
+   return mp_expt_n(a, (int)b, c);
+}
+#endif
+
+/* calculate c = a**b  using a square-multiply algorithm */
+mp_err mp_expt_n(const mp_int *a, int b, mp_int *c)
+{
+   mp_err err;
+   mp_int  g;
+
+   if ((err = mp_init_copy(&g, a)) != MP_OKAY) {
+      return err;
+   }
+
+   /* set initial result */
+   mp_set(c, 1uL);
+
+   while (b > 0) {
+      /* if the bit is set multiply */
+      if ((b & 1) != 0) {
+         if ((err = mp_mul(c, &g, c)) != MP_OKAY) {
+            goto LBL_ERR;
+         }
+      }
+
+      /* square */
+      if (b > 1) {
+         if ((err = mp_sqr(&g, &g)) != MP_OKAY) {
+            goto LBL_ERR;
+         }
+      }
+
+      /* shift to next bit */
+      b >>= 1;
+   }
+
+LBL_ERR:
+   mp_clear(&g);
+   return err;
+}
+
+#endif