X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/419d33ed2f44bd5f00b0c78a81aaa1abc37f2056..962dd3329d51f1d18313a17eb0cb4695ee4421a0:/mpbarrett.c

diff --git a/mpbarrett.c b/mpbarrett.c
index affbc65..b38aa91 100644
--- a/mpbarrett.c
+++ b/mpbarrett.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpbarrett.c,v 1.5 2000/07/29 17:04:33 mdw Exp $
+ * $Id: mpbarrett.c,v 1.8 2001/06/16 13:00:20 mdw Exp $
  *
  * Barrett modular reduction
  *
@@ -30,6 +30,15 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpbarrett.c,v $
+ * Revision 1.8  2001/06/16 13:00:20  mdw
+ * Use the generic exponentiation functions.
+ *
+ * Revision 1.7  2001/04/19 18:25:26  mdw
+ * Use sliding-window exponentiation.
+ *
+ * Revision 1.6  2000/10/08 12:03:44  mdw
+ * (mpbarrett_reduce): Cope with negative numbers.
+ *
  * Revision 1.5  2000/07/29 17:04:33  mdw
  * Change to use left-to-right bitwise exponentiation.  This will improve
  * performance when the base is small.
@@ -55,6 +64,7 @@
 
 #include "mp.h"
 #include "mpbarrett.h"
+#include "mpbarrett-exp.h"
 
 /*----- Main code ---------------------------------------------------------*/
 
@@ -114,8 +124,7 @@ void mpbarrett_destroy(mpbarrett *mb)
  * Returns:	The residue of @m@ modulo the number in the reduction
  *		context.
  *
- * Use:		Performs an efficient modular reduction.  The argument is
- *		assumed to be positive.
+ * Use:		Performs an efficient modular reduction.
  */
 
 mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
@@ -161,7 +170,7 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
     mpx_umul(r->v, r->vl, q->v + k + 1, q->vl, mb->m->v, mb->m->vl);
     MP_DEST(d, k + 1, r->f);
     mpx_usub(d->v, d->vl, m->v, mvl, r->v, r->vl);
-    d->f = (m->f | r->f) & MP_BURN;
+    d->f = (m->f | r->f) & (MP_BURN | MP_NEG);
     MP_DROP(r);
     MP_DROP(q);
     MP_DROP(m);
@@ -173,6 +182,13 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
   while (MPX_UCMP(d->v, d->vl, >=, mb->m->v, mb->m->vl))
     mpx_usub(d->v, d->vl, d->v, d->vl, mb->m->v, mb->m->vl);
 
+  /* --- Fix up the sign --- */
+
+  if (d->f & MP_NEG) {
+    mpx_usub(d->v, d->vl, mb->m->v, mb->m->vl, d->v, d->vl);
+    d->f &= ~MP_NEG;
+  }
+
   MP_SHRINK(d);
   return (d);
 }
@@ -189,60 +205,18 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
 
 mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
 {
-  mpscan sc;
   mp *x = MP_ONE;
   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
-  unsigned sq = 0;
-
-  a = MP_COPY(a);
-  mp_rscan(&sc, e);
-  if (!MP_RSTEP(&sc))
-    goto exit;
-  while (!MP_RBIT(&sc))
-    MP_RSTEP(&sc);
-
-  /* --- Do the main body of the work --- */
-
-  for (;;) {
-    sq++;
-    while (sq) {
-      mp *y;
-      y = mp_sqr(spare, x);
-      y = mpbarrett_reduce(mb, y, y);
-      spare = x; x = y;
-      sq--;
-    }
-    {
-      mp *y = mp_mul(spare, x, a);
-      y = mpbarrett_reduce(mb, y, y);
-      spare = x; x = y;
-    }
-    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 = mpbarrett_reduce(mb, y, y);
-    spare = x; x = y;
-    sq--;
-  }  
-
-exit:
-  MP_DROP(a);
-  if (spare != MP_NEW)
-    MP_DROP(spare);
-  if (d != MP_NEW)
-    MP_DROP(d);
+  MP_SHRINK(e);
+  if (!MP_LEN(e))
+    ;
+  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);
 }
 
@@ -262,7 +236,7 @@ static int vmod(dstr *v)
   mpbarrett_create(&mb, n);
   s = mpbarrett_reduce(&mb, MP_NEW, x);
 
-  if (MP_CMP(s, !=, r)) {
+  if (!MP_EQ(s, r)) {
     fputs("\n*** barrett reduction failure\n", stderr);
     fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr);
     fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr);
@@ -294,7 +268,7 @@ static int vexp(dstr *v)
 
   mr = mpbarrett_exp(&mb, MP_NEW, a, b);
 
-  if (MP_CMP(mr, !=, r)) {
+  if (!MP_EQ(mr, r)) {
     fputs("\n*** barrett modexp failed", stderr);
     fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);