X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/79a340293970d5f9b9c000f82769179f9ba551bd..aa1082f28ddd05f3b946ca1a9c6bfaa17d18aca5:/mpmont.c

diff --git a/mpmont.c b/mpmont.c
index 66b7657..7522dba 100644
--- a/mpmont.c
+++ b/mpmont.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpmont.c,v 1.3 1999/11/21 11:35:10 mdw Exp $
+ * $Id: mpmont.c,v 1.5 1999/11/22 13:58:40 mdw Exp $
  *
  * Montgomery reduction
  *
@@ -30,6 +30,15 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpmont.c,v $
+ * Revision 1.5  1999/11/22 13:58:40  mdw
+ * Add an option to disable Montgomery reduction, so that performance
+ * comparisons can be done.
+ *
+ * Revision 1.4  1999/11/21 12:27:06  mdw
+ * Remove a division from the Montgomery setup by calculating
+ * %$R^2 \bmod m$% first and then %$R \bmod m$% by Montgomery reduction of
+ * %$R^2$%.
+ *
  * Revision 1.3  1999/11/21 11:35:10  mdw
  * Performance improvement: use @mp_sqr@ and @mpmont_reduce@ instead of
  * @mpmont_mul@ for squaring in exponentiation.
@@ -48,6 +57,16 @@
 #include "mp.h"
 #include "mpmont.h"
 
+/*----- Tweakables --------------------------------------------------------*/
+
+/* --- @MPMONT_DISABLE@ --- *
+ *
+ * Replace all the clever Montgomery reduction with good old-fashioned long
+ * division.
+ */
+
+/* #define MPMONT_DISABLE */
+
 /*----- Main code ---------------------------------------------------------*/
 
 /* --- @mpmont_create@ --- *
@@ -60,6 +79,18 @@
  * Use:		Initializes a Montgomery reduction context ready for use.
  */
 
+#ifdef MPMONT_DISABLE
+
+void mpmont_create(mpmont *mm, mp *m)
+{
+  mp_shrink(m);
+  mm->m = MP_COPY(m);
+  mm->r = MP_ONE;
+  mm->r2 = MP_ONE;
+}
+
+#else
+
 void mpmont_create(mpmont *mm, mp *m)
 {
   /* --- Take a copy of the modulus --- */
@@ -92,19 +123,20 @@ void mpmont_create(mpmont *mm, mp *m)
 
   {
     size_t l = MP_LEN(m);
-    mp *r = mp_create(l + 1);
+    mp *r = mp_create(2 * l + 1);
 
     mm->shift = l * MPW_BITS;
     MPX_ZERO(r->v, r->vl - 1);
     r->vl[-1] = 1;
-    mm->r = mm->r2 = MP_NEW;
-    mp_div(0, &mm->r, r, m);
-    r = mp_sqr(r, mm->r);
+    mm->r2 = MP_NEW;
     mp_div(0, &mm->r2, r, m);
+    mm->r = mpmont_reduce(mm, MP_NEW, mm->r2);
     MP_DROP(r);
   }
 }
 
+#endif
+
 /* --- @mpmont_destroy@ --- *
  *
  * Arguments:	@mpmont *mm@ = pointer to a Montgomery reduction context
@@ -131,6 +163,16 @@ void mpmont_destroy(mpmont *mm)
  * Returns:	Result, %$a R^{-1} \bmod m$%.
  */
 
+#ifdef MPMONT_DISABLE
+
+mp *mpmont_reduce(mpmont *mm, mp *d, const mp *a)
+{
+  mp_div(0, &d, a, mm->m);
+  return (d);
+}
+
+#else
+
 mp *mpmont_reduce(mpmont *mm, mp *d, const mp *a)
 {
   mpw *dv, *dvl;
@@ -171,6 +213,8 @@ mp *mpmont_reduce(mpmont *mm, mp *d, const mp *a)
   return (d);
 }
 
+#endif
+
 /* --- @mpmont_mul@ --- *
  *
  * Arguments:	@mpmont *mm@ = pointer to Montgomery reduction context
@@ -180,6 +224,17 @@ mp *mpmont_reduce(mpmont *mm, mp *d, const mp *a)
  * Returns:	Result, %$a b R^{-1} \bmod m$%.
  */
 
+#ifdef MPMONT_DISABLE
+
+mp *mpmont_mul(mpmont *mm, mp *d, const mp *a, const mp *b)
+{
+  d = mp_mul(d, a, b);
+  mp_div(0, &d, d, mm->m);
+  return (d);
+}
+
+#else
+
 mp *mpmont_mul(mpmont *mm, mp *d, const mp *a, const mp *b)
 {
   mpw *dv, *dvl;
@@ -236,6 +291,8 @@ mp *mpmont_mul(mpmont *mm, mp *d, const mp *a, const mp *b)
   return (d);
 }
 
+#endif
+
 /* --- @mpmont_expr@ --- *
  *
  * Arguments:	@mpmont *mm@ = pointer to Montgomery reduction context