--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_reduce_2k.c	Mon May 31 18:25:22 2004 +0000
@@ -0,0 +1,56 @@
+/* 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>
+
+/* reduces a modulo n where n is of the form 2**p - d */
+int
+mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d)
+{
+   mp_int q;
+   int    p, res;
+   
+   if ((res = mp_init(&q)) != MP_OKAY) {
+      return res;
+   }
+   
+   p = mp_count_bits(n);    
+top:
+   /* q = a/2**p, a = a mod 2**p */
+   if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
+      goto ERR;
+   }
+   
+   if (d != 1) {
+      /* q = q * d */
+      if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) { 
+         goto ERR;
+      }
+   }
+   
+   /* a = a + q */
+   if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
+      goto ERR;
+   }
+   
+   if (mp_cmp_mag(a, n) != MP_LT) {
+      s_mp_sub(a, n, a);
+      goto top;
+   }
+   
+ERR:
+   mp_clear(&q);
+   return res;
+}
+