git.distorted.org.uk Git - u/mdw/catacomb/blob - gf-arith.c

   1 /* -*-c-*-
   2  *
   3  * $Id: gf-arith.c,v 1.1.2.1 2004/03/21 22:39:46 mdw Exp $
   4  *
   5  * Basic arithmetic on binary polynomials
   6  *
   7  * (c) 2004 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: gf-arith.c,v $
  33  * Revision 1.1.2.1  2004/03/21 22:39:46  mdw
  34  * Elliptic curves on binary fields work.
  35  *
  36  */
  37
  38 /*----- Header files ------------------------------------------------------*/
  39
  40 #include "gf.h"
  41
  42 /*----- Macros ------------------------------------------------------------*/
  43
  44 #define MAX(x, y) ((x) >= (y) ? (x) : (y))
  45
  46 /*----- Main code ---------------------------------------------------------*/
  47
  48 /* --- @gf_add@ --- *
  49  *
  50  * Arguments:   @mp *d@ = destination
  51  *              @mp *a, *b@ = sources
  52  *
  53  * Returns:     Result, @a@ added to @b@.
  54  */
  55
  56 mp *gf_add(mp *d, mp *a, mp *b)
  57 {
  58   MP_DEST(d, MAX(MP_LEN(a), MP_LEN(b)), (a->f | b->f) & MP_BURN);
  59   gfx_add(d->v, d->vl, a->v, a->vl, b->v, b->vl);
  60   d->f = (a->f | b->f) & MP_BURN;
  61   MP_SHRINK(d);
  62   return (d);
  63 }
  64
  65 /* --- @gf_mul@ --- *
  66  *
  67  * Arguments:   @mp *d@ = destination
  68  *              @mp *a, *b@ = sources
  69  *
  70  * Returns:     Result, @a@ multiplied by @b@.
  71  */
  72
  73 mp *gf_mul(mp *d, mp *a, mp *b)
  74 {
  75   a = MP_COPY(a);
  76   b = MP_COPY(b);
  77
  78   if (MP_LEN(a) <= MPK_THRESH || MP_LEN(b) <= GFK_THRESH) {
  79     MP_DEST(d, MP_LEN(a) + MP_LEN(b), a->f | b->f | MP_UNDEF);
  80     gfx_mul(d->v, d->vl, a->v, a->vl, b->v, b->vl);
  81   } else {
  82     size_t m = MAX(MP_LEN(a), MP_LEN(b));
  83     mpw *s;
  84     MP_DEST(d, 2 * m, a->f | b->f | MP_UNDEF);
  85     s = mpalloc(d->a, 2 * m);
  86     gfx_kmul(d->v, d->vl, a->v, a->vl, b->v, b->vl, s, s + 2 * m);
  87     mpfree(d->a, s);
  88   }
  89
  90   d->f = (a->f | b->f) & MP_BURN;
  91   MP_SHRINK(d);
  92   MP_DROP(a);
  93   MP_DROP(b);
  94   return (d);
  95 }
  96
  97 /* --- @gf_sqr@ --- *
  98  *
  99  * Arguments:   @mp *d@ = destination
 100  *              @mp *a@ = source
 101  *
 102  * Returns:     Result, @a@ squared.
 103  */
 104
 105 mp *gf_sqr(mp *d, mp *a)
 106 {
 107   MP_COPY(a);
 108   MP_DEST(d, 2 * MP_LEN(a), a->f & MP_BURN);
 109   gfx_sqr(d->v, d->vl, a->v, a->vl);
 110   d->f = a->f & MP_BURN;
 111   MP_SHRINK(d);
 112   MP_DROP(a);
 113   return (d);
 114 }
 115
 116 /* --- @gf_div@ --- *
 117  *
 118  * Arguments:   @mp **qq, **rr@ = destination, quotient and remainder
 119  *              @mp *a, *b@ = sources
 120  *
 121  * Use:         Calculates the quotient and remainder when @a@ is divided by
 122  *              @b@.  The destinations @*qq@ and @*rr@ must be distinct.
 123  *              Either of @qq@ or @rr@ may be null to indicate that the
 124  *              result is irrelevant.  (Discarding both results is silly.)
 125  *              There is a performance advantage if @a == *rr@.
 126  */
 127
 128 void gf_div(mp **qq, mp **rr, mp *a, mp *b)
 129  {
 130   mp *r = rr ? *rr : MP_NEW;
 131   mp *q = qq ? *qq : MP_NEW;
 132
 133   /* --- Set the remainder up right --- */
 134
 135   b = MP_COPY(b);
 136   a = MP_COPY(a);
 137   if (r)
 138     MP_DROP(r);
 139   r = a;
 140   MP_DEST(r, MP_LEN(b) + 2, a->f | b->f);
 141
 142   /* --- Fix up the quotient too --- */
 143
 144   r = MP_COPY(r);
 145   MP_DEST(q, MP_LEN(r), r->f | MP_UNDEF);
 146   MP_DROP(r);
 147
 148   /* --- Perform the calculation --- */
 149
 150   gfx_div(q->v, q->vl, r->v, r->vl, b->v, b->vl);
 151
 152   /* --- Sort out the sign of the results --- *
 153    *
 154    * If the signs of the arguments differ, and the remainder is nonzero, I
 155    * must add one to the absolute value of the quotient and subtract the
 156    * remainder from @b@.
 157    */
 158
 159   q->f = (r->f | b->f) & MP_BURN;
 160   r->f = (r->f | b->f) & MP_BURN;
 161
 162   /* --- Store the return values --- */
 163
 164   MP_DROP(b);
 165
 166   if (!qq)
 167     MP_DROP(q);
 168   else {
 169     MP_SHRINK(q);
 170     *qq = q;
 171   }
 172
 173   if (!rr)
 174     MP_DROP(r);
 175   else {
 176     MP_SHRINK(r);
 177     *rr = r;
 178   }
 179 }
 180
 181 /*----- Test rig ----------------------------------------------------------*/
 182
 183 #ifdef TEST_RIG
 184
 185 static int verify(const char *op, mp *expect, mp *result, mp *a, mp *b)
 186 {
 187   if (!MP_EQ(expect, result)) {
 188     fprintf(stderr, "\n*** %s failed", op);
 189     fputs("\n*** a      = ", stderr); mp_writefile(a, stderr, 16);
 190     fputs("\n*** b      = ", stderr); mp_writefile(b, stderr, 16);
 191     fputs("\n*** result = ", stderr); mp_writefile(result, stderr, 16);
 192     fputs("\n*** expect = ", stderr); mp_writefile(expect, stderr, 16);
 193     fputc('\n', stderr);
 194     return (0);
 195   }
 196   return (1);
 197 }
 198
 199 #define RIG(name, op)                                                   \
 200   static int t##name(dstr *v)                                           \
 201   {                                                                     \
 202     mp *a = *(mp **)v[0].buf;                                           \
 203     mp *b = *(mp **)v[1].buf;                                           \
 204     mp *r = *(mp **)v[2].buf;                                           \
 205     mp *c = op(MP_NEW, a, b);                                           \
 206     int ok = verify(#name, r, c, a, b);                                 \
 207     mp_drop(a); mp_drop(b); mp_drop(c); mp_drop(r);                     \
 208     assert(mparena_count(MPARENA_GLOBAL) == 0);                         \
 209     return (ok);                                                        \
 210   }
 211
 212 RIG(add, gf_add)
 213 RIG(mul, gf_mul)
 214
 215 #undef RIG
 216
 217 static int tsqr(dstr *v)
 218 {
 219   mp *a = *(mp **)v[0].buf;
 220   mp *r = *(mp **)v[1].buf;
 221   mp *c = MP_NEW;
 222   int ok = 1;
 223   c = gf_sqr(MP_NEW, a);
 224   ok &= verify("sqr", r, c, a, MP_ZERO);
 225   mp_drop(a); mp_drop(r); mp_drop(c);
 226   assert(mparena_count(MPARENA_GLOBAL) == 0);
 227   return (ok);
 228 }
 229
 230 static int tdiv(dstr *v)
 231 {
 232   mp *a = *(mp **)v[0].buf;
 233   mp *b = *(mp **)v[1].buf;
 234   mp *q = *(mp **)v[2].buf;
 235   mp *r = *(mp **)v[3].buf;
 236   mp *c = MP_NEW, *d = MP_NEW;
 237   int ok = 1;
 238   gf_div(&c, &d, a, b);
 239   ok &= verify("div(quotient)", q, c, a, b);
 240   ok &= verify("div(remainder)", r, d, a, b);
 241   mp_drop(a); mp_drop(b); mp_drop(c); mp_drop(d); mp_drop(r); mp_drop(q);
 242   assert(mparena_count(MPARENA_GLOBAL) == 0);
 243   return (ok);
 244 }
 245
 246 static test_chunk tests[] = {
 247   { "add", tadd, { &type_mp, &type_mp, &type_mp, 0 } },
 248   { "mul", tmul, { &type_mp, &type_mp, &type_mp, 0 } },
 249   { "sqr", tsqr, { &type_mp, &type_mp, 0 } },
 250   { "div", tdiv, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
 251   { 0, 0, { 0 } },
 252 };
 253
 254 int main(int argc, char *argv[])
 255 {
 256   sub_init();
 257   test_run(argc, argv, tests, SRCDIR "/tests/gf");
 258   return (0);
 259 }
 260
 261 #endif
 262
 263 /*----- That's all, folks -------------------------------------------------*/