diff libtommath/bn_mp_2expt.c @ 293:9d110777f345 contrib-blacklist

propagate from branch 'au.asn.ucc.matt.dropbear' (head 7ad1775ed65e75dbece27fe6b65bf1a234db386a) to branch 'au.asn.ucc.matt.dropbear.contrib.blacklist' (head 1d86a4f0a401cc68c2670d821a2f6366c37af143)
author Matt Johnston <matt@ucc.asn.au>
date Fri, 10 Mar 2006 06:31:29 +0000
parents eed26cff980b
children 5ff8218bcee9
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_2expt.c	Fri Mar 10 06:31:29 2006 +0000
@@ -0,0 +1,44 @@
+#include <tommath.h>
+#ifdef BN_MP_2EXPT_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, [email protected], http://math.libtomcrypt.org
+ */
+
+/* computes a = 2**b 
+ *
+ * Simple algorithm which zeroes the int, grows it then just sets one bit
+ * as required.
+ */
+int
+mp_2expt (mp_int * a, int b)
+{
+  int     res;
+
+  /* zero a as per default */
+  mp_zero (a);
+
+  /* grow a to accomodate the single bit */
+  if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
+    return res;
+  }
+
+  /* set the used count of where the bit will go */
+  a->used = b / DIGIT_BIT + 1;
+
+  /* put the single bit in its place */
+  a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
+
+  return MP_OKAY;
+}
+#endif