Release 2.1.4.

[u/mdw/catacomb] / gfreduce.c

diff --git a/gfreduce.c b/gfreduce.c
index 929c46c..f9b92c8 100644 (file)
--- a/gfreduce.c
+++ b/gfreduce.c
@@ -1,13 +1,13 @@
 /* -*-c-*-
  *
- * $Id: gfreduce.c,v 1.3 2004/03/23 15:19:32 mdw Exp $
+ * $Id$
  *
  * Efficient reduction modulo sparse binary polynomials
  *
  * (c) 2004 Straylight/Edgeware
  */
 
-/*----- Licensing notice --------------------------------------------------* 
+/*----- Licensing notice --------------------------------------------------*
  *
  * This file is part of Catacomb.
  *
@@ -15,32 +15,18 @@
  * it under the terms of the GNU Library General Public License as
  * published by the Free Software Foundation; either version 2 of the
  * License, or (at your option) any later version.
- * 
+ *
  * Catacomb is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Library General Public License for more details.
- * 
+ *
  * You should have received a copy of the GNU Library General Public
  * License along with Catacomb; if not, write to the Free
  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  * MA 02111-1307, USA.
  */
 
-/*----- Revision history --------------------------------------------------* 
- *
- * $Log: gfreduce.c,v $
- * Revision 1.3  2004/03/23 15:19:32  mdw
- * Test elliptic curves more thoroughly.
- *
- * Revision 1.2  2004/03/21 22:52:06  mdw
- * Merge and close elliptic curve branch.
- *
- * Revision 1.1.2.1  2004/03/21 22:39:46  mdw
- * Elliptic curves on binary fields work.
- *
- */
-
 /*----- Header files ------------------------------------------------------*/
 
 #include <mLib/alloc.h>
@@ -75,10 +61,10 @@ DA_DECL(instr_v, gfreduce_instr);
  * words to demonstrate what I'm talking about.
  *
  *  xxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx
- *                  001ppppp pppppppp pppppppp pppppppp
- *                    |<rp>|
- *                    |<------------ bp ------------->|
- *                  |<------------ nw --------------->|
+ *                 001ppppp pppppppp pppppppp pppppppp
+ *                   |<rp>|
+ *                   |<------------ bp ------------->|
+ *                 |<------------ nw --------------->|
  *
  * The trick of taking whole words off of @X@ stops working when there are
  * only @nw@ words left.  Then we have to mask off the bottom bits of @w@
@@ -98,12 +84,13 @@ DA_DECL(instr_v, gfreduce_instr);
 void gfreduce_create(gfreduce *r, mp *p)
 {
   instr_v iv = DA_INIT;
-  unsigned long d, dw;
+  unsigned long d;
+  unsigned dw;
   mpscan sc;
   unsigned long i;
   gfreduce_instr *ip;
   unsigned f = 0;
-  size_t w, ww, wi, wl, ll;
+  size_t w, ww, wi, wl, ll, bb;
 
   /* --- Sort out the easy stuff --- */
 
@@ -134,6 +121,7 @@ void gfreduce_create(gfreduce *r, mp *p)
   wi = DA_LEN(&iv);
   f = 0;
   ll = 0;
+  bb = MPW_BITS - dw;
   for (i = 0, mp_scan(&sc, p); mp_step(&sc) && i < d; i++) {
     if (!mp_bit(&sc))
       continue;
@@ -162,8 +150,8 @@ void gfreduce_create(gfreduce *r, mp *p)
       w = ww;
       wi = DA_LEN(&iv);
     }
-    INSTR(GFRI_LSL, (i - d)%MPW_BITS);
-    if ((i - d)%MPW_BITS)
+    INSTR(GFRI_LSL, (bb + i)%MPW_BITS);
+    if ((bb + i)%MPW_BITS)
       f |= f_lsr;
   }
   wl = DA_LEN(&iv);
@@ -351,7 +339,7 @@ int gfreduce_trace(gfreduce *r, mp *x)
     y = gfreduce_do(r, t, t);
     y = gf_add(y, y, x);
   }
-  rc = !MP_ISZERO(y);
+  rc = !MP_ZEROP(y);
   mp_drop(spare);
   mp_drop(y);
   return (rc);
@@ -423,7 +411,7 @@ mp *gfreduce_quadsolve(gfreduce *r, mp *d, mp *x)
        z = gf_add(z, z, t);
        w = gf_add(w, w, rho);
       }
-      if (!MP_ISZERO(w))
+      if (!MP_ZEROP(w))
        break;
       MP_DROP(z);
       MP_DROP(w);
@@ -450,11 +438,11 @@ mp *gfreduce_quadsolve(gfreduce *r, mp *d, mp *x)
 /* --- @gfreduce_exp@ --- *
  *
  * Arguments:  @gfreduce *gr@ = pointer to reduction context
- *              @mp *d@ = fake destination
- *              @mp *a@ = base
- *              @mp *e@ = exponent
+ *             @mp *d@ = fake destination
+ *             @mp *a@ = base
+ *             @mp *e@ = exponent
  *
- * Returns:     Result, %$a^e \bmod m$%.
+ * Returns:    Result, %$a^e \bmod m$%.
  */
 
 mp *gfreduce_exp(gfreduce *gr, mp *d, mp *a, mp *e)
@@ -463,13 +451,19 @@ mp *gfreduce_exp(gfreduce *gr, mp *d, mp *a, mp *e)
   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
 
   MP_SHRINK(e);
-  if (!MP_LEN(e))
+  MP_COPY(a);
+  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 = gf_modinv(a, a, gr->p);
+    if (MP_LEN(e) < EXP_THRESH)
+      EXP_SIMPLE(x, a, e);
+    else
+      EXP_WINDOW(x, a, e);
+  }
   mp_drop(d);
+  mp_drop(a);
   mp_drop(spare);
   return (x);
 }
@@ -580,7 +574,7 @@ static int vtr(dstr *v)
     ok = 0;
   }
   gfreduce_destroy(&rr);
-  mp_drop(p); mp_drop(x); 
+  mp_drop(p); mp_drop(x);
   assert(mparena_count(MPARENA_GLOBAL) == 0);
   return (ok);
 }