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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include "mpx.h"
  33 #include "gfx.h"
  34 #include "gfx-sqr-tab.h"
  35
  36 /*----- Static variables --------------------------------------------------*/
  37
  38 static const uint16 tab[256] = GFX_SQRTAB;
  39
  40 /*----- Main code ---------------------------------------------------------*/
  41
  42 /* --- @gfx_sqr@ --- *
  43  *
  44  * Arguments:   @mpw *dv, *dvl@ = destination vector base and limit
  45  *              @const mpw *av, *avl@ = argument vector base and limit
  46  *
  47  * Returns:     ---
  48  *
  49  * Use:         Performs squaring of binary polynomials.
  50  */
  51
  52 void gfx_sqr(mpw *dv, mpw *dvl, const mpw *av, const mpw *avl)
  53 {
  54   mpd a = 0, aa = 0;
  55   unsigned b = 0, bb = 0;
  56
  57   /* --- Simple stuff --- */
  58
  59   if (dv >= dvl)
  60     return;
  61   MPX_SHRINK(av, avl);
  62
  63   /* --- The main algorithm --- *
  64    *
  65    * Our method depends on the fact that, in a field of characteristic 2, we
  66    * have that %$(a + b)^2 = a^2 + b^2$%.  Thus, to square a polynomial, it's
  67    * sufficient just to put a zero bit between each of the bits of the
  68    * original argument.  We use a precomputed table for this, and work on
  69    * entire octets at a time.  Life is more complicated because we've got to
  70    * be careful of bizarre architectures which don't have words with a
  71    * multiple of 8 bits in them.
  72    */
  73
  74   for (;;) {
  75
  76     /* --- Input buffering --- */
  77
  78     if (b < 8) {
  79       if (av >= avl)
  80         break;
  81       a |= *av++ << b;
  82       b += MPW_BITS;
  83     }
  84
  85     /* --- Do the work in the middle --- */
  86
  87     aa |= (mpd)(tab[U8(a)]) << bb;
  88     bb += 16;
  89     a >>= 8;
  90     b -= 8;
  91
  92     /* --- Output buffering --- */
  93
  94     if (bb >= MPW_BITS) {
  95       *dv++ = MPW(aa);
  96       if (dv >= dvl)
  97         return;
  98       aa >>= MPW_BITS;
  99       bb -= MPW_BITS;
 100     }
 101   }
 102
 103   /* --- Flush the input buffer --- */
 104
 105   if (b) for (;;) {
 106     aa |= (mpd)(tab[U8(a)]) << bb;
 107     bb += 16;
 108     if (bb > MPW_BITS) {
 109       *dv++ = MPW(aa);
 110       if (dv >= dvl)
 111         return;
 112       aa >>= MPW_BITS;
 113       bb -= MPW_BITS;
 114     }
 115     a >>= 8;
 116     if (b <= 8)
 117       break;
 118     else
 119       b -= 8;
 120   }
 121
 122   /* --- Flush the output buffer --- */
 123
 124   if (bb) for (;;) {
 125     *dv++ = MPW(aa);
 126     if (dv >= dvl)
 127       return;
 128     aa >>= MPW_BITS;
 129     if (bb <= MPW_BITS)
 130       break;
 131     else
 132       bb -= MPW_BITS;
 133   }
 134
 135   /* --- Zero the rest of everything --- */
 136
 137   MPX_ZERO(dv, dvl);
 138 }
 139
 140 /*----- Test rig ----------------------------------------------------------*/
 141
 142 #ifdef TEST_RIG
 143
 144 #include <mLib/alloc.h>
 145 #include <mLib/dstr.h>
 146 #include <mLib/quis.h>
 147 #include <mLib/testrig.h>
 148
 149 #define ALLOC(v, vl, sz) do {                                           \
 150   size_t _sz = (sz);                                                    \
 151   mpw *_vv = xmalloc(MPWS(_sz));                                        \
 152   mpw *_vvl = _vv + _sz;                                                \
 153   (v) = _vv;                                                            \
 154   (vl) = _vvl;                                                          \
 155 } while (0)
 156
 157 #define LOAD(v, vl, d) do {                                             \
 158   const dstr *_d = (d);                                                 \
 159   mpw *_v, *_vl;                                                        \
 160   ALLOC(_v, _vl, MPW_RQ(_d->len));                                      \
 161   mpx_loadb(_v, _vl, _d->buf, _d->len);                                 \
 162   (v) = _v;                                                             \
 163   (vl) = _vl;                                                           \
 164 } while (0)
 165
 166 #define MAX(x, y) ((x) > (y) ? (x) : (y))
 167
 168 static void dumpmp(const char *msg, const mpw *v, const mpw *vl)
 169 {
 170   fputs(msg, stderr);
 171   MPX_SHRINK(v, vl);
 172   while (v < vl)
 173     fprintf(stderr, " %08lx", (unsigned long)*--vl);
 174   fputc('\n', stderr);
 175 }
 176
 177 static int vsqr(dstr *v)
 178 {
 179   mpw *a, *al;
 180   mpw *b, *bl;
 181   mpw *d, *dl;
 182   int ok = 1;
 183
 184   LOAD(a, al, &v[0]);
 185   LOAD(b, bl, &v[1]);
 186   ALLOC(d, dl, 2 * (al - a));
 187
 188   gfx_sqr(d, dl, a, al);
 189   if (!mpx_ueq(d, dl, b, bl)) {
 190     fprintf(stderr, "\n*** vsqr failed\n");
 191     dumpmp("       a", a, al);
 192     dumpmp("expected", b, bl);
 193     dumpmp("  result", d, dl);
 194     ok = 0;
 195   }
 196
 197   xfree(a); xfree(b); xfree(d);
 198   return (ok);
 199 }
 200
 201 static test_chunk defs[] = {
 202   { "sqr", vsqr, { &type_hex, &type_hex, 0 } },
 203   { 0, 0, { 0 } }
 204 };
 205
 206 int main(int argc, char *argv[])
 207 {
 208   test_run(argc, argv, defs, SRCDIR"/tests/gfx");
 209   return (0);
 210 }
 211
 212 #endif
 213
 214 /*----- That's all, folks -------------------------------------------------*/