git.distorted.org.uk Git - u/mdw/catacomb/blob - gfx-sqr.c

   1 /* -*-c-*-
   2  *
   3  * $Id: gfx-sqr.c,v 1.1.4.1 2004/03/21 22:39:46 mdw Exp $
   4  *
   5  * Sqaring binary polynomials
   6  *
   7  * (c) 2000 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: gfx-sqr.c,v $
  33  * Revision 1.1.4.1  2004/03/21 22:39:46  mdw
  34  * Elliptic curves on binary fields work.
  35  *
  36  * Revision 1.1  2000/10/08 15:49:37  mdw
  37  * First glimmerings of binary polynomial arithmetic.
  38  *
  39  */
  40
  41 /*----- Header files ------------------------------------------------------*/
  42
  43 #include "mpx.h"
  44 #include "gfx.h"
  45 #include "gfx-sqr-tab.h"
  46
  47 /*----- Static variables --------------------------------------------------*/
  48
  49 static uint16 tab[256] = GFX_SQRTAB;
  50
  51 /*----- Main code ---------------------------------------------------------*/
  52
  53 /* --- @gfx_sqr@ --- *
  54  *
  55  * Arguments:   @mpw *dv, *dvl@ = destination vector base and limit
  56  *              @const mpw *av, *avl@ = argument vector base and limit
  57  *
  58  * Returns:     ---
  59  *
  60  * Use:         Performs squaring of binary polynomials.
  61  */
  62
  63 void gfx_sqr(mpw *dv, mpw *dvl, const mpw *av, const mpw *avl)
  64 {
  65   mpd a = 0, aa = 0;
  66   unsigned b = 0, bb = 0;
  67
  68   /* --- Simple stuff --- */
  69
  70   if (dv >= dvl)
  71     return;
  72   MPX_SHRINK(av, avl);
  73
  74   /* --- The main algorithm --- *
  75    *
  76    * Our method depends on the fact that, in a field of characteristic 2, we
  77    * have that %$(a + b)^2 = a^2 + b^2$%.  Thus, to square a polynomial, it's
  78    * sufficient just to put a zero bit between each of the bits of the
  79    * original argument.  We use a precomputed table for this, and work on
  80    * entire octets at a time.  Life is more complicated because we've got to
  81    * be careful of bizarre architectures which don't have words with a
  82    * multiple of 8 bits in them.
  83    */
  84
  85   for (;;) {
  86
  87     /* --- Input buffering --- */
  88
  89     if (b < 8) {
  90       if (av >= avl)
  91         break;
  92       a |= *av++ << b;
  93       b += MPW_BITS;
  94     }
  95
  96     /* --- Do the work in the middle --- */
  97
  98     aa |= (mpd)(tab[U8(a)]) << bb;
  99     bb += 16;
 100     a >>= 8;
 101     b -= 8;
 102
 103     /* --- Output buffering --- */
 104
 105     if (bb >= MPW_BITS) {
 106       *dv++ = MPW(aa);
 107       if (dv >= dvl)
 108         return;
 109       aa >>= MPW_BITS;
 110       bb -= MPW_BITS;
 111     }
 112   }
 113
 114   /* --- Flush the input buffer --- */
 115
 116   if (b) for (;;) {
 117     aa |= (mpd)(tab[U8(a)]) << bb;
 118     bb += 16;
 119     if (bb > MPW_BITS) {
 120       *dv++ = MPW(aa);
 121       if (dv >= dvl)
 122         return;
 123       aa >>= MPW_BITS;
 124       bb -= MPW_BITS;
 125     }
 126     a >>= 8;
 127     if (b <= 8)
 128       break;
 129     else
 130       b -= 8;
 131   }
 132
 133   /* --- Flush the output buffer --- */
 134
 135   if (bb) for (;;) {
 136     *dv++ = MPW(aa);
 137     if (dv >= dvl)
 138       return;
 139     aa >>= MPW_BITS;
 140     if (bb <= MPW_BITS)
 141       break;
 142     else
 143       bb -= MPW_BITS;
 144   }
 145
 146   /* --- Zero the rest of everything --- */
 147
 148   MPX_ZERO(dv, dvl);
 149 }
 150
 151 /*----- Test rig ----------------------------------------------------------*/
 152
 153 #ifdef TEST_RIG
 154
 155 #include <mLib/alloc.h>
 156 #include <mLib/dstr.h>
 157 #include <mLib/quis.h>
 158 #include <mLib/testrig.h>
 159
 160 #define ALLOC(v, vl, sz) do {                                           \
 161   size_t _sz = (sz);                                                    \
 162   mpw *_vv = xmalloc(MPWS(_sz));                                        \
 163   mpw *_vvl = _vv + _sz;                                                \
 164   (v) = _vv;                                                            \
 165   (vl) = _vvl;                                                          \
 166 } while (0)
 167
 168 #define LOAD(v, vl, d) do {                                             \
 169   const dstr *_d = (d);                                                 \
 170   mpw *_v, *_vl;                                                        \
 171   ALLOC(_v, _vl, MPW_RQ(_d->len));                                      \
 172   mpx_loadb(_v, _vl, _d->buf, _d->len);                                 \
 173   (v) = _v;                                                             \
 174   (vl) = _vl;                                                           \
 175 } while (0)
 176
 177 #define MAX(x, y) ((x) > (y) ? (x) : (y))
 178
 179 static void dumpmp(const char *msg, const mpw *v, const mpw *vl)
 180 {
 181   fputs(msg, stderr);
 182   MPX_SHRINK(v, vl);
 183   while (v < vl)
 184     fprintf(stderr, " %08lx", (unsigned long)*--vl);
 185   fputc('\n', stderr);
 186 }
 187
 188 static int vsqr(dstr *v)
 189 {
 190   mpw *a, *al;
 191   mpw *b, *bl;
 192   mpw *d, *dl;
 193   int ok = 1;
 194
 195   LOAD(a, al, &v[0]);
 196   LOAD(b, bl, &v[1]);
 197   ALLOC(d, dl, 2 * (al - a));
 198
 199   gfx_sqr(d, dl, a, al);
 200   if (!mpx_ueq(d, dl, b, bl)) {
 201     fprintf(stderr, "\n*** vsqr failed\n");
 202     dumpmp("       a", a, al);
 203     dumpmp("expected", b, bl);
 204     dumpmp("  result", d, dl);
 205     ok = 0;
 206   }
 207
 208   free(a); free(b); free(d);
 209   return (ok);
 210 }
 211
 212 static test_chunk defs[] = {
 213   { "sqr", vsqr, { &type_hex, &type_hex, 0 } },
 214   { 0, 0, { 0 } }
 215 };
 216
 217 int main(int argc, char *argv[])
 218 {
 219   test_run(argc, argv, defs, SRCDIR"/tests/gfx");
 220   return (0);
 221 }
 222
 223 #endif
 224
 225 /*----- That's all, folks -------------------------------------------------*/