### diff libtommath/bn_mp_reduce_is_2k.c @ 284:eed26cff980b

author Matt Johnston Wed, 08 Mar 2006 13:23:49 +0000 5ff8218bcee9
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```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_reduce_is_2k.c	Wed Mar 08 13:23:49 2006 +0000
@@ -0,0 +1,48 @@
+#include <tommath.h>
+#ifdef BN_MP_REDUCE_IS_2K_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 if mp_reduce_2k can be used */
+int mp_reduce_is_2k(mp_int *a)
+{
+   int ix, iy, iw;
+   mp_digit iz;
+
+   if (a->used == 0) {
+      return MP_NO;
+   } else if (a->used == 1) {
+      return MP_YES;
+   } else if (a->used > 1) {
+      iy = mp_count_bits(a);
+      iz = 1;
+      iw = 1;
+
+      /* Test every bit from the second digit up, must be 1 */
+      for (ix = DIGIT_BIT; ix < iy; ix++) {
+          if ((a->dp[iw] & iz) == 0) {
+             return MP_NO;
+          }
+          iz <<= 1;
+          if (iz > (mp_digit)MP_MASK) {
+             ++iw;
+             iz = 1;
+          }
+      }
+   }
+   return MP_YES;
+}
+
+#endif```