diff bn_mp_reduce_2k_setup.c @ 282:91fbc376f010 libtommath-orig libtommath-0.35

Import of libtommath 0.35 From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:16:18 +0000
parents
children 97db060d0ef5
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_reduce_2k_setup.c	Wed Mar 08 13:16:18 2006 +0000
@@ -0,0 +1,43 @@
+#include <tommath.h>
+#ifdef BN_MP_REDUCE_2K_SETUP_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
+ */
+
+/* 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;
+}
+#endif