X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/932f6ca7358aee875a5f6fc0c6a33ead4100fa30..4640a0dd947f422cfda780c62da342792af27b7b:/mpmont.c

diff --git a/mpmont.c b/mpmont.c
index d051778..2371de8 100644
--- a/mpmont.c
+++ b/mpmont.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpmont.c,v 1.14 2001/02/22 09:04:26 mdw Exp $
+ * $Id: mpmont.c,v 1.15 2001/06/16 13:00:20 mdw Exp $
  *
  * Montgomery reduction
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpmont.c,v $
+ * Revision 1.15  2001/06/16 13:00:20  mdw
+ * Use the generic exponentiation functions.
+ *
  * Revision 1.14  2001/02/22 09:04:26  mdw
  * Cosmetic fix.
  *
@@ -88,6 +91,7 @@
 
 #include "mp.h"
 #include "mpmont.h"
+#include "mpmont-exp.h"
 
 /*----- Tweakables --------------------------------------------------------*/
 
@@ -99,7 +103,7 @@
 
 /* #define MPMONT_DISABLE */
 
-/*----- Main code ---------------------------------------------------------*/
+/*----- Reduction and multiplication --------------------------------------*/
 
 /* --- @mpmont_create@ --- *
  *
@@ -363,6 +367,8 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
 
 #endif
 
+/*----- Exponentiation ----------------------------------------------------*/
+
 /* --- @mpmont_expr@ --- *
  *
  * Arguments:	@mpmont *mm@ = pointer to Montgomery reduction context
@@ -370,190 +376,21 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
  *		@mp *a@ = base
  *		@mp *e@ = exponent
  *
- * Returns:	Result, %$a^e R \bmod m$%.
+ * Returns:	Result, %$(a R^{-1})^e R \bmod m$%.
  */
 
-#define WINSZ 5
-#define TABSZ (1 << (WINSZ - 1))
-
-#define THRESH (((MPW_BITS / WINSZ) << 2) + 1)
-
-static mp *exp_simple(mpmont *mm, mp *d, mp *a, mp *e)
-{
-  mpscan sc;
-  mp *ar;
-  mp *x = MP_COPY(mm->r);
-  mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
-  unsigned sq = 0;
-
-  mp_rscan(&sc, e);
-  if (!MP_RSTEP(&sc))
-    goto exit;
-  while (!MP_RBIT(&sc))
-    MP_RSTEP(&sc);
-
-  /* --- Do the main body of the work --- */
-  
-  ar = mpmont_mul(mm, MP_NEW, a, mm->r2);
-  for (;;) {
-    sq++;
-    while (sq) {
-      mp *y;
-      y = mp_sqr(spare, x);
-      y = mpmont_reduce(mm, y, y);
-      spare = x; x = y;
-      sq--;
-    }
-    { mp *y = mpmont_mul(mm, spare, x, ar); spare = x; x = y; }
-    sq = 0;
-    for (;;) {
-      if (!MP_RSTEP(&sc))
-	goto done;
-      if (MP_RBIT(&sc))
-	break;
-      sq++;
-    }
-  }
-
-  /* --- Do a final round of squaring --- */
-
-done:
-  while (sq) {
-    mp *y;
-    y = mp_sqr(spare, x);
-    y = mpmont_reduce(mm, y, y);
-    spare = x; x = y;
-    sq--;
-  }
-
-  /* --- Done --- */
-
-  MP_DROP(ar);
-exit:
-  if (spare != MP_NEW)
-    MP_DROP(spare);
-  if (d != MP_NEW)
-    MP_DROP(d);
-  return (x);
-}
-
 mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
 {
-  mp **tab;
-  mp *ar, *a2;
-  mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
   mp *x = MP_COPY(mm->r);
-  unsigned i, sq = 0;
-  mpscan sc;
-
-  /* --- Do we bother? --- */
+  mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
 
   MP_SHRINK(e);
   if (MP_LEN(e) == 0)
-    goto exit;
-  if (MP_LEN(e) < THRESH) {
-    x->ref--;
-    return (exp_simple(mm, d, a, e));
-  }
-
-  /* --- Do the precomputation --- */
-
-  ar = mpmont_mul(mm, MP_NEW, a, mm->r2);
-  a2 = mp_sqr(MP_NEW, ar);
-  a2 = mpmont_reduce(mm, a2, a2);
-  tab = xmalloc(TABSZ * sizeof(mp *));
-  tab[0] = ar;
-  for (i = 1; i < TABSZ; i++)
-    tab[i] = mpmont_mul(mm, MP_NEW, tab[i - 1], a2);
-  mp_drop(a2);
-  mp_rscan(&sc, e);
-
-  /* --- Skip top-end zero bits --- *
-   *
-   * If the initial step worked, there must be a set bit somewhere, so keep
-   * stepping until I find it.
-   */
-
-  MP_RSTEP(&sc);
-  while (!MP_RBIT(&sc))
-    MP_RSTEP(&sc);
-
-  /* --- Now for the main work --- */
-
-  for (;;) {
-    unsigned l = 0;
-    unsigned z = 0;
-
-    /* --- The next bit is set, so read a window index --- *
-     *
-     * Reset @i@ to zero and increment @sq@.  Then, until either I read
-     * @WINSZ@ bits or I run out of bits, scan in a bit: if it's clear, bump
-     * the @z@ counter; if it's set, push a set bit into @i@, shift it over
-     * by @z@ bits, bump @sq@ by @z + 1@ and clear @z@.  By the end of this
-     * palaver, @i@ is an index to the precomputed value in @tab@.
-     */
-
-    i = 0;
-    sq++;
-    for (;;) {
-      l++;
-      if (l >= WINSZ || !MP_RSTEP(&sc))
-	break;
-      if (!MP_RBIT(&sc))
-	z++;
-      else {
-	i = ((i << 1) | 1) << z;
-	sq += z + 1;
-	z = 0;
-      }
-    }
-
-    /* --- Do the squaring --- *
-     *
-     * Remember that @sq@ carries over from the zero-skipping stuff below.
-     */
-
-    while (sq) {
-      mp *y;
-      y = mp_sqr(spare, x);
-      y = mpmont_reduce(mm, y, y);
-      spare = x; x = y;
-      sq--;
-    }
-
-    /* --- Do the multiply --- */
-
-    { mp *y = mpmont_mul(mm, spare, x, tab[i]); spare = x; x = y; }
-
-    /* --- Now grind along through the rest of the bits --- */
-
-    sq = z;
-    for (;;) {
-      if (!MP_RSTEP(&sc))
-	goto done;
-      if (MP_RBIT(&sc))
-	break;
-      sq++;
-    }
-  }
-
-  /* --- Do a final round of squaring --- */
-
-done:
-  while (sq) {
-    mp *y;
-    y = mp_sqr(spare, x);
-    y = mpmont_reduce(mm, y, y);
-    spare = x; x = y;
-    sq--;
-  }
-
-  /* --- Done --- */
-
-  for (i = 0; i < TABSZ; i++)
-    mp_drop(tab[i]);
-  xfree(tab);
-exit:
+    ;
+  else if (MP_LEN(e) < EXP_THRESH)
+    EXP_SIMPLE(x, a, e);
+  else
+    EXP_WINDOW(x, a, e);
   mp_drop(d);
   mp_drop(spare);
   return (x);
@@ -571,7 +408,8 @@ exit:
 
 mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e)
 {
-  d = mpmont_expr(mm, d, a, e);
+  d = mpmont_mul(mm, d, a, mm->r2);
+  d = mpmont_expr(mm, d, d, e);
   d = mpmont_reduce(mm, d, d);
   return (d);
 }