diff bn_mp_reduce_2k_setup.c @ 1:22d5cf7d4b1a libtommath

Renaming branch
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
parents
children d29b64170cf0
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_reduce_2k_setup.c	Mon May 31 18:23:46 2004 +0000
@@ -0,0 +1,42 @@
+/* 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
+ */
+#include <tommath.h>
+
+/* determines the setup value */
+int 
+mp_reduce_2k_setup(mp_int *a, mp_digit *d)
+{
+   int res, p;
+   mp_int tmp;
+   
+   if ((res = mp_init(&tmp)) != MP_OKAY) {
+      return res;
+   }
+   
+   p = mp_count_bits(a);
+   if ((res = mp_2expt(&tmp, p)) != MP_OKAY) {
+      mp_clear(&tmp);
+      return res;
+   }
+   
+   if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
+      mp_clear(&tmp);
+      return res;
+   }
+   
+   *d = tmp.dp[0];
+   mp_clear(&tmp);
+   return MP_OKAY;
+}