math/gfreduce.[ch]: Fix out-of-bounds memory access.

[u/mdw/catacomb] / math / gfx-sqr.c

/* -*-c-*-
 *
 * Sqaring binary polynomials
 *
 * (c) 2000 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * 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.
 */

/*----- Header files ------------------------------------------------------*/

#include "mpx.h"
#include "gfx.h"

/*----- Static variables --------------------------------------------------*/

extern const uint16 gfx_sqrtab[256];

/*----- Main code ---------------------------------------------------------*/

/* --- @gfx_sqr@ --- *
 *
 * Arguments:	@mpw *dv, *dvl@ = destination vector base and limit
 *		@const mpw *av, *avl@ = argument vector base and limit
 *
 * Returns:	---
 *
 * Use:		Performs squaring of binary polynomials.
 */

void gfx_sqr(mpw *dv, mpw *dvl, const mpw *av, const mpw *avl)
{
  mpd a = 0, aa = 0;
  unsigned b = 0, bb = 0;

  /* --- Simple stuff --- */

  if (dv >= dvl)
    return;
  MPX_SHRINK(av, avl);

  /* --- The main algorithm --- *
   *
   * Our method depends on the fact that, in a field of characteristic 2, we
   * have that %$(a + b)^2 = a^2 + b^2$%.  Thus, to square a polynomial, it's
   * sufficient just to put a zero bit between each of the bits of the
   * original argument.  We use a precomputed table for this, and work on
   * entire octets at a time.  Life is more complicated because we've got to
   * be careful of bizarre architectures which don't have words with a
   * multiple of 8 bits in them.
   */

  for (;;) {

    /* --- Input buffering --- */

    if (b < 8) {
      if (av >= avl)
	break;
      a |= *av++ << b;
      b += MPW_BITS;
    }

    /* --- Do the work in the middle --- */

    aa |= (mpd)(gfx_sqrtab[U8(a)]) << bb;
    bb += 16;
    a >>= 8;
    b -= 8;

    /* --- Output buffering --- */

    if (bb >= MPW_BITS) {
      *dv++ = MPW(aa);
      if (dv >= dvl)
	return;
      aa >>= MPW_BITS;
      bb -= MPW_BITS;
    }
  }

  /* --- Flush the input buffer --- */

  if (b) for (;;) {
    aa |= (mpd)(gfx_sqrtab[U8(a)]) << bb;
    bb += 16;
    if (bb > MPW_BITS) {
      *dv++ = MPW(aa);
      if (dv >= dvl)
	return;
      aa >>= MPW_BITS;
      bb -= MPW_BITS;
    }
    a >>= 8;
    if (b <= 8)
      break;
    else
      b -= 8;
  }

  /* --- Flush the output buffer --- */

  if (bb) for (;;) {
    *dv++ = MPW(aa);
    if (dv >= dvl)
      return;
    aa >>= MPW_BITS;
    if (bb <= MPW_BITS)
      break;
    else
      bb -= MPW_BITS;
  }

  /* --- Zero the rest of everything --- */

  MPX_ZERO(dv, dvl);
}

/*----- Test rig ----------------------------------------------------------*/

#ifdef TEST_RIG

#include <mLib/alloc.h>
#include <mLib/dstr.h>
#include <mLib/quis.h>
#include <mLib/testrig.h>

#define ALLOC(v, vl, sz) do {						\
  size_t _sz = (sz);							\
  mpw *_vv = xmalloc(MPWS(_sz));					\
  mpw *_vvl = _vv + _sz;						\
  (v) = _vv;								\
  (vl) = _vvl;								\
} while (0)

#define LOAD(v, vl, d) do {						\
  const dstr *_d = (d);							\
  mpw *_v, *_vl;							\
  ALLOC(_v, _vl, MPW_RQ(_d->len));					\
  mpx_loadb(_v, _vl, _d->buf, _d->len);					\
  (v) = _v;								\
  (vl) = _vl;								\
} while (0)

#define MAX(x, y) ((x) > (y) ? (x) : (y))

static void dumpmp(const char *msg, const mpw *v, const mpw *vl)
{
  fputs(msg, stderr);
  MPX_SHRINK(v, vl);
  while (v < vl)
    fprintf(stderr, " %08lx", (unsigned long)*--vl);
  fputc('\n', stderr);
}

static int vsqr(dstr *v)
{
  mpw *a, *al;
  mpw *b, *bl;
  mpw *d, *dl;
  int ok = 1;

  LOAD(a, al, &v[0]);
  LOAD(b, bl, &v[1]);
  ALLOC(d, dl, 2 * (al - a));

  gfx_sqr(d, dl, a, al);
  if (!mpx_ueq(d, dl, b, bl)) {
    fprintf(stderr, "\n*** vsqr failed\n");
    dumpmp("	   a", a, al);
    dumpmp("expected", b, bl);
    dumpmp("  result", d, dl);
    ok = 0;
  }

  xfree(a); xfree(b); xfree(d);
  return (ok);
}

static test_chunk defs[] = {
  { "sqr", vsqr, { &type_hex, &type_hex, 0 } },
  { 0, 0, { 0 } }
};

int main(int argc, char *argv[])
{
  test_run(argc, argv, defs, SRCDIR"/t/gfx");
  return (0);
}

#endif

/*----- That's all, folks -------------------------------------------------*/