Rearrange the file tree.

[u/mdw/catacomb] / mp-sqrt.c

diff --git a/mp-sqrt.c b/mp-sqrt.c
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-/* -*-c-*-
- *
- * $Id$
- *
- * Compute integer square roots
- *
- * (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 "mp.h"
-
-/*----- Main code ---------------------------------------------------------*/
-
-/* --- @mp_sqrt@ --- *
- *
- * Arguments:  @mp *d@ = pointer to destination integer
- *             @mp *a@ = (nonnegative) integer to take square root of
- *
- * Returns:    The largest integer %$x$% such that %$x^2 \le a$%.
- *
- * Use:                Computes integer square roots.
- *
- *             The current implementation isn't very good: it uses the
- *             Newton-Raphson method to find an approximation to %$a$%.  If
- *             there's any demand for a better version, I'll write one.
- */
-
-mp *mp_sqrt(mp *d, mp *a)
-{
-  unsigned long z;
-  mp *q = MP_NEW, *r = MP_NEW;
-
-  /* --- Sanity preservation --- */
-
-  assert(!MP_NEGP(a));
-
-  /* --- Deal with trivial cases --- */
-
-  MP_SHRINK(a);
-  if (MP_ZEROP(a)) {
-    mp_drop(d);
-    return (MP_ZERO);
-  }
-
-  /* --- Find an initial guess of about the right size --- */
-
-  z = mp_bits(a);
-  z >>= 1;
-  mp_copy(a);
-  d = mp_lsr(d, a, z);
-
-  /* --- Main approximation --- *
-   *
-   * We use the Newton-Raphson recurrence relation
-   *
-   *   %$x_{i+1} = x_i - \frac{x_i^2 - a}{2 x_i}$%
-   *
-   * We inspect the term %$q = x^2 - a$% to see when to stop.  Increasing
-   * %$x$% is pointless when %$-q < 2 x + 1$%.
-   */
-
-  for (;;) {
-    q = mp_sqr(q, d);
-    q = mp_sub(q, q, a);
-    if (MP_ZEROP(q))
-      break;
-    if (MP_NEGP(q)) {
-      r = mp_lsl(r, d, 1);
-      r->f |= MP_NEG;
-      if (MP_CMP(q, >=, r))
-       break;
-    }
-    mp_div(&r, &q, q, d);
-    r = mp_lsr(r, r, 1);
-    if (r->v == r->vl)
-      d = mp_sub(d, d, MP_ONE);
-    else
-      d = mp_sub(d, d, r);
-  }
-
-  /* --- Finished, at last --- */
-
-  mp_drop(a);
-  mp_drop(q);
-  mp_drop(r);
-  return (d);
-}
-
-/*----- Test rig ----------------------------------------------------------*/
-
-#ifdef TEST_RIG
-
-#include <mLib/testrig.h>
-
-static int verify(dstr *v)
-{
-  mp *a = *(mp **)v[0].buf;
-  mp *qq = *(mp **)v[1].buf;
-  mp *q = mp_sqrt(MP_NEW, a);
-  int ok = 1;
-
-  if (!MP_EQ(q, qq)) {
-    ok = 0;
-    fputs("\n*** sqrt failed", stderr);
-    fputs("\n*** a     = ", stderr); mp_writefile(a, stderr, 10);
-    fputs("\n*** result = ", stderr); mp_writefile(q, stderr, 10);
-    fputs("\n*** expect = ", stderr); mp_writefile(qq, stderr, 10);
-    fputc('\n', stderr);
-  }
-
-  mp_drop(a);
-  mp_drop(q);
-  mp_drop(qq);
-  assert(mparena_count(MPARENA_GLOBAL) == 0);
-
-  return (ok);
-}
-
-static test_chunk tests[] = {
-  { "sqrt", verify, { &type_mp, &type_mp, 0 } },
-  { 0, 0, { 0 } },
-};
-
-int main(int argc, char *argv[])
-{
-  sub_init();
-  test_run(argc, argv, tests, SRCDIR "/tests/mp");
-  return (0);
-}
-
-#endif
-
-/*----- That's all, folks -------------------------------------------------*/