--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_montgomery_calc_normalization.c	Mon May 31 18:23:46 2004 +0000
@@ -0,0 +1,53 @@
+/* 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>
+
+/* calculates a = B^n mod b for Montgomery reduction
+ * Where B is the base [e.g. 2^DIGIT_BIT].
+ * B^n mod b is computed by first computing
+ * A = B^(n-1) which doesn't require a reduction but a simple OR.
+ * then C = A * B = B^n is computed by performing upto DIGIT_BIT
+ * shifts with subtractions when the result is greater than b.
+ *
+ * The method is slightly modified to shift B unconditionally upto just under
+ * the leading bit of b.  This saves alot of multiple precision shifting.
+ */
+int
+mp_montgomery_calc_normalization (mp_int * a, mp_int * b)
+{
+  int     x, bits, res;
+
+  /* how many bits of last digit does b use */
+  bits = mp_count_bits (b) % DIGIT_BIT;
+
+  /* compute A = B^(n-1) * 2^(bits-1) */
+  if ((res = mp_2expt (a, (b->used - 1) * DIGIT_BIT + bits - 1)) != MP_OKAY) {
+    return res;
+  }
+
+  /* now compute C = A * B mod b */
+  for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
+    if ((res = mp_mul_2 (a, a)) != MP_OKAY) {
+      return res;
+    }
+    if (mp_cmp_mag (a, b) != MP_LT) {
+      if ((res = s_mp_sub (a, b, a)) != MP_OKAY) {
+        return res;
+      }
+    }
+  }
+
+  return MP_OKAY;
+}