catcrypt: Implement symmetric key-encapsulation and signature schemes.

[u/mdw/catacomb] / mpmont-exp.c

diff --git a/mpmont-exp.c b/mpmont-exp.c
index c43d02f..0caf118 100644 (file)
--- a/mpmont-exp.c
+++ b/mpmont-exp.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpmont-exp.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
  *
  * Modular exponentiation with Montgomery reduction
  *
@@ -52,17 +52,19 @@ mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
 
   MP_COPY(a);
   MP_SHRINK(e);
-  if (e->f & MP_NEG) {
-    a = mpmont_reduce(mm, a, a);
-    a = mp_modinv(a, a, mm->m);
-    a = mpmont_mul(mm, a, a, mm->r2);
-  }
-  if (MP_LEN(e) == 0)
+  if (MP_ZEROP(e))
     ;
-  else if (MP_LEN(e) < EXP_THRESH)
-    EXP_SIMPLE(x, a, e);
-  else
-    EXP_WINDOW(x, a, e);
+  else {
+    if (MP_NEGP(e)) {
+      a = mpmont_reduce(mm, a, a);
+      a = mp_modinv(a, a, mm->m);
+      a = mpmont_mul(mm, a, a, mm->r2);
+    }
+    if (MP_LEN(e) < EXP_THRESH)
+      EXP_SIMPLE(x, a, e);
+    else
+      EXP_WINDOW(x, a, e);
+  }
   mp_drop(d);
   mp_drop(spare);
   mp_drop(a);