/*
 * zfunc - extended precision integral arithmetic non-primitive routines
 *
 * Copyright (C) 1999-2007,2021-2023  David I. Bell, Landon Curt Noll and Ernest Bowen
 *
 * Primary author:  David I. Bell
 *
 * Calc is open software; you can redistribute it and/or modify it under
 * the terms of the version 2.1 of the GNU Lesser General Public License
 * as published by the Free Software Foundation.
 *
 * Calc 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 Lesser General
 * Public License for more details.
 *
 * A copy of version 2.1 of the GNU Lesser General Public License is
 * distributed with calc under the filename COPYING-LGPL.  You should have
 * received a copy with calc; if not, write to Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * Under source code control:   1990/02/15 01:48:27
 * File existed as early as:    before 1990
 *
 * Share and enjoy!  :-)        http://www.isthe.com/chongo/tech/comp/calc/
 */


#include "zmath.h"
#include "alloc.h"


#include "errtbl.h"
#include "banned.h"     /* include after system header <> includes */


ZVALUE _tenpowers_[TEN_MAX+1];          /* table of 10^2^n */

STATIC long *power10 = NULL;
STATIC int max_power10_exp = 0;

/*
 * given:
 *
 *      unsigned long x
 * or:  unsigned long long x
 * or:  long x                  and  x >= 0
 * or:  long long x             and  x >= 0
 *
 * If issq_mod4k[x & 0xfff] == 0, then x cannot be a perfect square
 * else x might be a perfect square.
 */
STATIC USB8 issq_mod4k[1<<12] = {
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        1,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
        0,1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
};


/*
 * Compute the factorial of a number.
 */
void
zfact(ZVALUE z, ZVALUE *dest)
{
        long ptwo;              /* count of powers of two */
        long n;                 /* current multiplication value */
        long m;                 /* reduced multiplication value */
        long mul;               /* collected value to multiply by */
        ZVALUE res, temp;

        /* firewall */
        if (dest == NULL) {
                math_error("%s: dest NULL", __func__);
                not_reached();
        }

        if (zisneg(z)) {
                math_error("Negative argument for factorial");
                not_reached();
        }
        if (zge31b(z)) {
                math_error("Very large factorial");
                not_reached();
        }
        n = ztolong(z);
        ptwo = 0;
        mul = 1;
        res = _one_;
        /*
         * Multiply numbers together, but squeeze out all powers of two.
         * We will put them back in at the end.  Also collect multiple
         * numbers together until there is a risk of overflow.
         */
        for (; n > 1; n--) {
                for (m = n; ((m & 0x1) == 0); m >>= 1)
                        ptwo++;
                if (mul <= MAXLONG/m) {
                        mul *= m;
                        continue;
                }
                zmuli(res, mul, &temp);
                zfree(res);
                res = temp;
                mul = m;
        }
        /*
         * Multiply by the remaining value, then scale result by
         * the proper power of two.
         */
        if (mul > 1) {
                zmuli(res, mul, &temp);
                zfree(res);
                res = temp;
        }
        zshift(res, ptwo, &temp);
        zfree(res);
        *dest = temp;
}


/*
 * Compute the permutation function  M! / (M - N)!.
 */
void
zperm(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        SFULL count;
        ZVALUE cur, tmp, ans;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (zisneg(z1) || zisneg(z2)) {
                math_error("Negative argument for permutation");
                not_reached();
        }
        if (zrel(z1, z2) < 0) {
                math_error("Second arg larger than first in permutation");
                not_reached();
        }
        if (zge31b(z2)) {
                math_error("Very large permutation");
                not_reached();
        }
        count = ztolong(z2);
        zcopy(z1, &ans);
        zsub(z1, _one_, &cur);
        while (--count > 0) {
                zmul(ans, cur, &tmp);
                zfree(ans);
                ans = tmp;
                zsub(cur, _one_, &tmp);
                zfree(cur);
                cur = tmp;
        }
        zfree(cur);
        *res = ans;
}

/*
 * docomb evaluates binomial coefficient when z1 >= 0, z2 >= 0
 */
S_FUNC int
docomb(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        ZVALUE ans;
        ZVALUE mul, div, temp;
        FULL count, i;
#if BASEB == 16
        HALF dh[2];
#else
        HALF dh[1];
#endif

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (zrel(z2, z1) > 0)
                return 0;
        zsub(z1, z2, &temp);

        if (zge31b(z2) && zge31b(temp)) {
                zfree(temp);
                return -2;
        }
        if (zrel(temp, z2) < 0)
                count = ztofull(temp);
        else
                count = ztofull(z2);
        zfree(temp);
        if (count == 0)
                return 1;
        if (count == 1)
                return 2;
        div.sign = 0;
        div.v = dh;
        div.len = 1;
        zcopy(z1, &mul);
        zcopy(z1, &ans);
        for (i = 2; i <= count; i++) {
#if BASEB == 16
                dh[0] = (HALF)(i & BASE1);
                dh[1] = (HALF)(i >> BASEB);
                div.len = 1 + (dh[1] != 0);
#else
                dh[0] = (HALF) i;
#endif
                zsub(mul, _one_, &temp);
                zfree(mul);
                mul = temp;
                zmul(ans, mul, &temp);
                zfree(ans);
                zquo(temp, div, &ans, 0);
                zfree(temp);
        }
        zfree(mul);
        *res = ans;
        return 3;
}

/*
 * Compute the combinatorial function  M! / ( N! * (M - N)! ).
 * Returns 0 if result is 0
*          1      1
*          2      z1
*         -1      -1
*         -2    if too complicated
*          3    result stored at res
 */
int
zcomb(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        ZVALUE z3, z4;
        int r;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (z2.sign || (!z1.sign && zrel(z2, z1) > 0))
                return 0;
        if (zisone(z2))
                return 2;
        if (z1.sign) {
                z1.sign = 0;
                zsub(z1, _one_, &z3);
                zadd(z3, z2, &z4);
                zfree(z3);
                r = docomb(z4, z2, res);
                if (r == 2) {
                        *res = z4;
                        r = 3;
                }
                else
                        zfree(z4);
                if (z2.v[0] & 1) {
                        if (r == 1)
                                r = -1;
                        if (r == 3)
                                res->sign = 1;
                }
                return r;
        }
        return docomb(z1, z2, res);
}


/*
 * Compute the Jacobi function (m / n) for odd n.
 *
 * The property of the Jacobi function is: If n>2 is prime then
 *
 *      the result is 1 if m == x^2 (mod n) for some x.
 *      otherwise the result is -1.
 *
 * If n is not prime, then the result does not prove that n is not prime
 * when the value of the Jacobi is 1.
 *
 * Jacobi evaluation of (m / n), where n > 0 is odd AND m > 0 is odd:
 *
 *      rule 0: (0 / n) == 0
 *      rule 1: (1 / n) == 1
 *      rule 2: (m / n) == (a / n)      if m == a % n
 *      rule 3: (m / n) == (2*m / n)    if n == 1 % 8 OR n == 7 % 8
 *      rule 4: (m / n) == -(2*m / n)   if n != 1 & 8 AND n != 7 % 8
 *      rule 5: (m / n) == (n / m)      if m == 3 % 4 AND n == 3 % 4
 *      rule 6: (m / n) == -(n / m)     if m != 3 % 4 OR n != 3 % 4
 *
 * NOTE: This function returns 0 in invalid Jacobi parameters:
 *       m < 0 OR n is even OR n < 1.
 */
FLAG
zjacobi(ZVALUE z1, ZVALUE z2)
{
        ZVALUE p, q, tmp;
        long lowbit;
        int val;

        /* firewall */
        if (ziszero(z1) || zisneg(z1))
                return 0;
        if (ziseven(z2) || zisneg(z2))
                return 0;

        /* assume a value of 1 unless we find otherwise */
        if (zisone(z1))
                return 1;
        val = 1;
        zcopy(z1, &p);
        zcopy(z2, &q);
        for (;;) {
                zmod(p, q, &tmp, 0);
                zfree(p);
                p = tmp;
                if (ziszero(p)) {
                        zfree(p);
                        zfree(q);
                        return 0;
                }
                if (ziseven(p)) {
                        lowbit = zlowbit(p);
                        zshift(p, -lowbit, &tmp);
                        zfree(p);
                        p = tmp;
                        if ((lowbit & 1) && (((*q.v & 0x7) == 3) ||
                            ((*q.v & 0x7) == 5)))
                                val = -val;
                }
                if (zisunit(p)) {
                        zfree(p);
                        zfree(q);
                        return val;
                }
                if ((*p.v & *q.v & 0x3) == 3)
                        val = -val;
                tmp = q;
                q = p;
                p = tmp;
        }
}


/*
 * Return the Fibonacci number F(n).
 * This is evaluated by recursively using the formulas:
 *      F(2N+1) = F(N+1)^2 + F(N)^2
 * and
 *      F(2N) = F(N+1)^2 - F(N-1)^2
 */
void
zfib(ZVALUE z, ZVALUE *res)
{
        long n;
        int sign;
        ZVALUE fnm1, fn, fnp1;          /* consecutive Fibonacci values */
        ZVALUE t1, t2, t3;
        FULL i;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (zge31b(z)) {
                math_error("Very large Fibonacci number");
                not_reached();
        }
        n = ztolong(z);
        if (n == 0) {
                *res = _zero_;
                return;
        }
        sign = z.sign && ((n & 0x1) == 0);
        if (n <= 2) {
                *res = _one_;
                res->sign = (bool)sign;
                return;
        }
        i = TOPFULL;
        while ((i & n) == 0)
                i >>= (FULL)1;
        i >>= (FULL)1;
        fnm1 = _zero_;
        fn = _one_;
        fnp1 = _one_;
        while (i) {
                zsquare(fnm1, &t1);
                zsquare(fn, &t2);
                zsquare(fnp1, &t3);
                zfree(fnm1);
                zfree(fn);
                zfree(fnp1);
                zadd(t2, t3, &fnp1);
                zsub(t3, t1, &fn);
                zfree(t1);
                zfree(t2);
                zfree(t3);
                if (i & n) {
                        fnm1 = fn;
                        fn = fnp1;
                        zadd(fnm1, fn, &fnp1);
                } else {
                        zsub(fnp1, fn, &fnm1);
                }
                i >>= (FULL)1;
        }
        zfree(fnm1);
        zfree(fnp1);
        *res = fn;
        res->sign = (bool)sign;
}


/*
 * Compute the result of raising one number to the power of another
 * The second number is assumed to be non-negative.
 * It cannot be too large except for trivial cases.
 */
void
zpowi(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        int sign;               /* final sign of number */
        unsigned long power;    /* power to raise to */
        FULL bit;               /* current bit value */
        long twos;              /* count of times 2 is in result */
        ZVALUE ans, temp;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        sign = (z1.sign && zisodd(z2));
        z1.sign = 0;
        z2.sign = 0;
        if (ziszero(z2) && !ziszero(z1)) {      /* number raised to power 0 */
                *res = _one_;
                return;
        }
        if (zisabsleone(z1)) {  /* 0, 1, or -1 raised to a power */
                ans = _one_;
                ans.sign = (bool)sign;
                if (*z1.v == 0)
                        ans = _zero_;
                *res = ans;
                return;
        }
        if (zge31b(z2)) {
                math_error("Raising to very large power");
                not_reached();
        }
        power = ztoulong(z2);
        if (zistwo(z1)) {       /* two raised to a power */
                zbitvalue((long) power, res);
                return;
        }
        /*
         * See if this is a power of ten
         */
        if (zistiny(z1) && (*z1.v == 10)) {
                ztenpow((long) power, res);
                res->sign = (bool)sign;
                return;
        }
        /*
         * Handle low powers specially
         */
        if (power <= 4) {
                switch ((int) power) {
                case 1:
                        ans.len = z1.len;
                        ans.v = alloc(ans.len);
                        zcopyval(z1, ans);
                        ans.sign = (bool)sign;
                        *res = ans;
                        return;
                case 2:
                        zsquare(z1, res);
                        return;
                case 3:
                        zsquare(z1, &temp);
                        zmul(z1, temp, res);
                        zfree(temp);
                        res->sign = (bool)sign;
                        return;
                case 4:
                        zsquare(z1, &temp);
                        zsquare(temp, res);
                        zfree(temp);
                        return;
                }
        }
        /*
         * Shift out all powers of twos so the multiplies are smaller.
         * We will shift back the right amount when done.
         */
        twos = 0;
        if (ziseven(z1)) {
                twos = zlowbit(z1);
                ans.v = alloc(z1.len);
                ans.len = z1.len;
                ans.sign = z1.sign;
                zcopyval(z1, ans);
                zshiftr(ans, twos);
                ztrim(&ans);
                z1 = ans;
                twos *= power;
        }
        /*
         * Compute the power by squaring and multiplying.
         * This uses the left to right method of power raising.
         */
        bit = TOPFULL;
        while ((bit & power) == 0)
                bit >>= 1;
        bit >>= 1;
        zsquare(z1, &ans);
        if (bit & power) {
                zmul(ans, z1, &temp);
                zfree(ans);
                ans = temp;
        }
        bit >>= 1;
        while (bit) {
                zsquare(ans, &temp);
                zfree(ans);
                ans = temp;
                if (bit & power) {
                        zmul(ans, z1, &temp);
                        zfree(ans);
                        ans = temp;
                }
                bit >>= 1;
        }
        /*
         * Scale back up by proper power of two
         */
        if (twos) {
                zshift(ans, twos, &temp);
                zfree(ans);
                ans = temp;
                zfree(z1);
        }
        ans.sign = (bool)sign;
        *res = ans;
}


/*
 * Compute ten to the specified power
 * This saves some work since the squares of ten are saved.
 */
void
ztenpow(long power, ZVALUE *res)
{
        long i;
        ZVALUE ans;
        ZVALUE temp;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (power <= 0) {
                *res = _one_;
                return;
        }
        ans = _one_;
        _tenpowers_[0] = _ten_;
        for (i = 0; power; i++) {
                if (_tenpowers_[i].len == 0) {
                        if (i <= TEN_MAX) {
                                zsquare(_tenpowers_[i-1], &_tenpowers_[i]);
                        } else {
                                math_error("cannot compute 10^2^(TEN_MAX+1)");
                                not_reached();
                        }
                }
                if (power & 0x1) {
                        zmul(ans, _tenpowers_[i], &temp);
                        zfree(ans);
                        ans = temp;
                }
                power /= 2;
        }
        *res = ans;
}


/*
 * Calculate modular inverse suppressing unnecessary divisions.
 * This is based on the Euclidean algorithm for large numbers.
 * (Algorithm X from Knuth Vol 2, section 4.5.2. and exercise 17)
 * Returns true if there is no solution because the numbers
 * are not relatively prime.
 */
bool
zmodinv(ZVALUE u, ZVALUE v, ZVALUE *res)
{
        FULL    q1, q2, ui3, vi3, uh, vh, A, B, C, D, T;
        ZVALUE  u2, u3, v2, v3, qz, tmp1, tmp2, tmp3;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        v.sign = 0;
        if (zisneg(u) || (zrel(u, v) >= 0))
                zmod(u, v, &v3, 0);
        else
                zcopy(u, &v3);
        zcopy(v, &u3);
        u2 = _zero_;
        v2 = _one_;

        /*
         * Loop here while the size of the numbers remain above
         * the size of a HALF.  Throughout this loop u3 >= v3.
         */
        while ((u3.len > 1) && !ziszero(v3)) {
                vh = 0;
#if LONG_BITS == BASEB
                uh =  u3.v[u3.len - 1];
                if (v3.len == u3.len)
                        vh = v3.v[v3.len - 1];
#else
                uh = (((FULL) u3.v[u3.len - 1]) << BASEB) + u3.v[u3.len - 2];
                if ((v3.len + 1) >= u3.len)
                        vh = v3.v[v3.len - 1];
                if (v3.len == u3.len)
                        vh = (vh << BASEB) + v3.v[v3.len - 2];
#endif
                A = 1;
                B = 0;
                C = 0;
                D = 1;

                /*
                 * Calculate successive quotients of the continued fraction
                 * expansion using only single precision arithmetic until
                 * greater precision is required.
                 */
                while ((vh + C) && (vh + D)) {
                        q1 = (uh + A) / (vh + C);
                        q2 = (uh + B) / (vh + D);
                        if (q1 != q2)
                                break;
                        T = A - q1 * C;
                        A = C;
                        C = T;
                        T = B - q1 * D;
                        B = D;
                        D = T;
                        T = uh - q1 * vh;
                        uh = vh;
                        vh = T;
                }

                /*
                 * If B is zero, then we made no progress because
                 * the calculation requires a very large quotient.
                 * So we must do this step of the calculation in
                 * full precision
                 */
                if (B == 0) {
                        zquo(u3, v3, &qz, 0);
                        zmul(qz, v2, &tmp1);
                        zsub(u2, tmp1, &tmp2);
                        zfree(tmp1);
                        zfree(u2);
                        u2 = v2;
                        v2 = tmp2;
                        zmul(qz, v3, &tmp1);
                        zsub(u3, tmp1, &tmp2);
                        zfree(tmp1);
                        zfree(u3);
                        u3 = v3;
                        v3 = tmp2;
                        zfree(qz);
                        continue;
                }
                /*
                 * Apply the calculated A,B,C,D numbers to the current
                 * values to update them as if the full precision
                 * calculations had been carried out.
                 */
                zmuli(u2, (long) A, &tmp1);
                zmuli(v2, (long) B, &tmp2);
                zadd(tmp1, tmp2, &tmp3);
                zfree(tmp1);
                zfree(tmp2);
                zmuli(u2, (long) C, &tmp1);
                zmuli(v2, (long) D, &tmp2);
                zfree(u2);
                zfree(v2);
                u2 = tmp3;
                zadd(tmp1, tmp2, &v2);
                zfree(tmp1);
                zfree(tmp2);
                zmuli(u3, (long) A, &tmp1);
                zmuli(v3, (long) B, &tmp2);
                zadd(tmp1, tmp2, &tmp3);
                zfree(tmp1);
                zfree(tmp2);
                zmuli(u3, (long) C, &tmp1);
                zmuli(v3, (long) D, &tmp2);
                zfree(u3);
                zfree(v3);
                u3 = tmp3;
                zadd(tmp1, tmp2, &v3);
                zfree(tmp1);
                zfree(tmp2);
        }

        /*
         * Here when the remaining numbers become single precision in size.
         * Finish the procedure using single precision calculations.
         */
        if (ziszero(v3) && !zisone(u3)) {
                zfree(u3);
                zfree(v3);
                zfree(u2);
                zfree(v2);
                return true;
        }
        ui3 = ztofull(u3);
        vi3 = ztofull(v3);
        zfree(u3);
        zfree(v3);
        while (vi3) {
                q1 = ui3 / vi3;
                zmuli(v2, (long) q1, &tmp1);
                zsub(u2, tmp1, &tmp2);
                zfree(tmp1);
                zfree(u2);
                u2 = v2;
                v2 = tmp2;
                q2 = ui3 - q1 * vi3;
                ui3 = vi3;
                vi3 = q2;
        }
        zfree(v2);
        if (ui3 != 1) {
                zfree(u2);
                return true;
        }
        if (zisneg(u2)) {
                zadd(v, u2, res);
                zfree(u2);
                return false;
        }
        *res = u2;
        return false;
}


/*
 * Compute the greatest common divisor of a pair of integers.
 */
void
zgcd(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        int h, i, j, k;
        LEN len, l, m, n, o, p, q;
        HALF u, v, w, x;
        HALF *a, *a0, *A, *b, *b0, *B, *c, *d;
        FULL f, g;
        ZVALUE gcd;
        bool needw;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (zisunit(z1) || zisunit(z2)) {
                *res = _one_;
                return;
        }
        z1.sign = 0;
        z2.sign = 0;
        if (ziszero(z1) || !zcmp(z1, z2)) {
                zcopy(z2, res);
                return;
        }
        if (ziszero(z2)) {
                zcopy(z1, res);
                return;
        }

        o = 0;
        while (!(z1.v[o] | z2.v[o])) o++;       /* Count common zero digits */

        c = z1.v + o;
        d = z2.v + o;

        m = z1.len - o;
        n = z2.len - o;
        u = *c | *d;                    /* Count common zero bits */
        v = 1;
        p = 0;
        while (!(u & v)) {
                v <<= 1;
                p++;
        }

        while (!*c) {                           /* Removing zero digits */
                c++;
                m--;
        }

        while (!*d) {
                d++;
                n--;
        }


        u = *d;                 /* Count zero bits for *d */
        v = 1;
        q = 0;
        while (!(u & v)) {
                v <<= 1;
                q++;
        }

        a0 = A = alloc(m);
        b0 = B = alloc(n);

        memcpy(A, c, m * sizeof(HALF));                 /* Copy c[] to A[] */

                                /* Copy d[] to B[], shifting if necessary */
        if (q) {
                i = n;
                b = B + n;
                d += n;
                f = 0;
                while (i--) {
                        f = f << BASEB | *--d;
                        *--b = (HALF) (f >> q);
                }
                if (B[n-1] == 0) n--;
        }
        else memcpy(B, d, n * sizeof(HALF));

        if (n == 1) {           /* One digit case; use Euclid's algorithm */
                n = m;
                b0 = A;
                m = 1;
                a0 = B;
                if (m == 1) {                           /* a has one digit */
                        v = *a0;
                        if (v > 1) {                    /* Euclid's algorithm */
                                b = b0 + n;
                                i = n;
                                u = 0;
                                while (i--) {
                                        f = (FULL) u << BASEB | *--b;
                                        u = (HALF) (f % v);
                                }
                                while (u) { w = v % u; v = u; u = w; }
                        }
                        *b0 = v;
                        n = 1;
                }
                len = n + o;
                gcd.v = alloc(len + 1);
                /* Common zero digits */
                if (o) memset(gcd.v, 0, o * sizeof(HALF));
                /* Left shift for common zero bits */
                if (p) {
                        i = n;
                        f = 0;
                        b = b0;
                        a = gcd.v + o;
                        while (i--) {
                                f = f >> BASEB | (FULL) *b++ << p;
                                *a++ = (HALF) f;
                        }
                        if (f >>= BASEB) {len++; *a = (HALF) f;}
                } else {
                        memcpy(gcd.v + o, b0, n * sizeof(HALF));
                }
                gcd.len = len;
                gcd.sign = 0;
                freeh(A);
                freeh(B);
                *res = gcd;
                return;
        }

        u = B[n-1];                             /* Bit count for b */
        k = (n  - 1) * BASEB;
        while (u >>= 1) k++;

        needw = true;

        w = 0;
        j = 0;
        while (m) {                             /* START OF MAIN LOOP */
           if (m - n < 2 || needw) {
                q = 0;
                u = *a0;
                v = 1;
                while (!(u & v)) {              /* count zero bits for *a0 */
                        q++;
                        v <<= 1;
                }

                if (q) {                        /* right-justify a */
                        a = a0 + m;
                        i = m;
                        f = 0;
                        while (i--) {
                                f = f << BASEB | *--a;
                                *a = (HALF) (f >> q);
                        }
                        if (!a0[m-1]) m--;      /* top digit vanishes */
                }

                if (m == 1) break;

                u = a0[m-1];
                j = (m - 1) * BASEB;
                while (u >>= 1) j++;            /* counting bits for a */
                h = j - k;
                if (h < 0) {                    /* swapping to get h > 0 */
                        l = m;
                        m = n;
                        n = l;
                        a = a0;
                        a0 = b0;
                        b0 = a;
                        k = j;
                        h = -h;
                        needw = true;
                }
                if (h > 1) {
                        if (needw) {            /* find w = minv(*b0, h0) */
                                u = 1;
                                v = *b0;
                                w = 0;
                                x = 1;
                                i = h;
                                while (i-- && x) {
                                        if (u & x) { u -= v * x; w |= x;}
                                        x <<= 1;
                                }
                                needw = false;
                        }
                        g = (FULL) (*a0 * w);
                        if (h < BASEB) {
                            g &= (FULL)lowhalf[h];
                        } else {
                            g &= BASE1;
                        }
                } else {
                        g = 1;
                }
            } else {
                g = (FULL) (*a0 * w);
            }
            a = a0;
            b = b0;
            i = n;
            if (g > 1) {                        /* a - g * b case */
                    f = 0;
                    while (i--) {
                            f = (FULL) *a - g * *b++ - f;
                            *a++ = (HALF) f;
                            f >>= BASEB;
                            f = -f & BASE1;
                    }
                    if (f) {
                            i = m - n;
                            while (i-- && f) {
                                    f = *a - f;
                                    *a++ = (HALF) f;
                                    f >>= BASEB;
                                    f = -f & BASE1;
                            }
                    }
                    while (m && !*a0) { /* Removing trailing zeros */
                            m--;
                            a0++;
                    }
                    if (f) {            /* a - g * b < 0 */
                            while (m > 1 && a0[m-1] == BASE1) m--;
                            *a0 = - *a0;
                            a = a0;
                            i = m;
                            while (--i) {
                                    a++;
                                    *a = ~*a;
                            }
                    }
            } else {                            /* abs(a - b) case */
                    while (i && *a++ == *b++) i--;
                    q = n - i;
                    if (m == n) {               /* a and b same length */
                            if (i) {     /* a not equal to b */
                                    while (m && a0[m-1] == b0[m-1]) m--;
                                    if (a0[m-1] < b0[m-1]) {
                                            /* Swapping since a < b */
                                            a = a0;
                                            a0 = b0;
                                            b0 = a;
                                            k = j;
                                    }
                                    a = a0 + q;
                                    b = b0 + q;
                                    i = m - q;
                                    f = 0;
                                    while (i--) {
                                            f = (FULL) *a - *b++ - f;
                                            *a++ = (HALF) f;
                                            f >>= BASEB;
                                            f = -f & BASE1;
                                    }
                            }
                    } else {            /* a has more digits than b */
                            a = a0 + q;
                            b = b0 + q;
                            i = n - q;
                            f = 0;
                            while (i--) {
                                    f = (FULL) *a - *b++ - f;
                                    *a++ = (HALF) f;
                                    f >>= BASEB;
                                    f = -f & BASE1;
                            }
                            if (f) { while (!*a) *a++ = BASE1;
                                    (*a)--;
                            }
                    }
                    a0 += q;
                    m -= q;
                    while (m && !*a0) { /* Removing trailing zeros */
                            m--;
                            a0++;
                    }
            }
            while (m && !a0[m-1]) m--;  /* Removing leading zeros */
        }
        if (m == 1) {                           /* a has one digit */
                v = *a0;
                if (v > 1) {                    /* Euclid's algorithm */
                        b = b0 + n;
                        i = n;
                        u = 0;
                        while (i--) {
                                f = (FULL) u << BASEB | *--b;
                                u = (HALF) (f % v);
                        }
                        while (u) { w = v % u; v = u; u = w; }
                }
                *b0 = v;
                n = 1;
        }
        len = n + o;
        gcd.v = alloc(len + 1);
        if (o) memset(gcd.v, 0, o * sizeof(HALF));      /* Common zero digits */
        if (p) {                        /* Left shift for common zero bits */
                i = n;
                f = 0;
                b = b0;
                a = gcd.v + o;
                while (i--) {
                        f = (FULL) *b++ << p | f;
                        *a++ = (HALF) f;
                        f >>= BASEB;
                }
                if (f) {
                        len++; *a = (HALF) f;
                }
        } else {
                memcpy(gcd.v + o, b0, n * sizeof(HALF));
        }
        gcd.len = len;
        gcd.sign = 0;
        freeh(A);
        freeh(B);
        *res = gcd;
        return;
}

/*
 * Compute the lcm of two integers (least common multiple).
 * This is done using the formula:  gcd(a,b) * lcm(a,b) = a * b.
 */
void
zlcm(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        ZVALUE temp1, temp2;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        zgcd(z1, z2, &temp1);
        zequo(z1, temp1, &temp2);
        zfree(temp1);
        zmul(temp2, z2, res);
        zfree(temp2);
}


/*
 * Return whether or not two numbers are relatively prime to each other.
 */
bool
zrelprime(ZVALUE z1, ZVALUE z2)
{
        FULL rem1, rem2;                /* remainders */
        ZVALUE rem;
        bool result;

        z1.sign = 0;
        z2.sign = 0;
        if (ziseven(z1) && ziseven(z2)) /* false if both even */
                return false;
        if (zisunit(z1) || zisunit(z2)) /* true if either is a unit */
                return true;
        if (ziszero(z1) || ziszero(z2)) /* false if either is zero */
                return false;
        if (zistwo(z1) || zistwo(z2))   /* true if either is two */
                return true;
        /*
         * Try reducing each number by the product of the first few odd primes
         * to see if any of them are a common factor.
         */
        rem1 = zmodi(z1, (FULL)3 * 5 * 7 * 11 * 13);
        rem2 = zmodi(z2, (FULL)3 * 5 * 7 * 11 * 13);
        if (((rem1 % 3) == 0) && ((rem2 % 3) == 0))
                return false;
        if (((rem1 % 5) == 0) && ((rem2 % 5) == 0))
                return false;
        if (((rem1 % 7) == 0) && ((rem2 % 7) == 0))
                return false;
        if (((rem1 % 11) == 0) && ((rem2 % 11) == 0))
                return false;
        if (((rem1 % 13) == 0) && ((rem2 % 13) == 0))
                return false;
        /*
         * Try a new batch of primes now
         */
        rem1 = zmodi(z1, (FULL)17 * 19 * 23);
        rem2 = zmodi(z2, (FULL)17 * 19 * 23);
        if (((rem1 % 17) == 0) && ((rem2 % 17) == 0))
                return false;
        if (((rem1 % 19) == 0) && ((rem2 % 19) == 0))
                return false;
        if (((rem1 % 23) == 0) && ((rem2 % 23) == 0))
                return false;
        /*
         * Yuk, we must actually compute the gcd to know the answer
         */
        zgcd(z1, z2, &rem);
        result = zisunit(rem);
        zfree(rem);
        return result;
}


/*
 * Compute the integer floor of the log of an integer to a specified base.
 * The signs of the integers and base are ignored.
 * Example:  zlog(123456, 10) = 5.
 */
long
zlog(ZVALUE z, ZVALUE base)
{
        ZVALUE *zp;                     /* current square */
        long power;                     /* current power */
        ZVALUE temp;                    /* temporary */
        ZVALUE squares[32];             /* table of squares of base */

        /* ignore signs */

        z.sign = 0;
        base.sign = 0;

        /*
         * Make sure that the numbers are nonzero and the base is > 1
         */
        if (ziszero(z) || ziszero(base) || zisone(base)) {
                math_error("Zero or too small argument argument for zlog!!!");
                not_reached();
        }

        /*
         * Some trivial cases.
         */
        power = zrel(z, base);
        if (power <= 0)
                return (power + 1);

        /* base - power of two */
        if (zisonebit(base))
                return (zhighbit(z) / zlowbit(base));

        /* base = 10 */
        if (base.len == 1 && base.v[0] == 10)
                return zlog10(z, NULL);
        /*
         * Now loop by squaring the base each time, and see whether or
         * not each successive square is still smaller than the number.
         */
        zp = &squares[0];
        *zp = base;
        while (zp->len * 2 - 1 <= z.len  && zrel(z, *zp) > 0) {
                /* while square not too large */
                zsquare(*zp, zp + 1);
                zp++;
        }

        /*
         * Now back down the squares,
         */
        power = 0;
        for (; zp > squares; zp--) {
                if (zrel(z, *zp) >= 0) {
                        zquo(z, *zp, &temp, 0);
                        if (power)
                                zfree(z);
                        z = temp;
                        power++;
                }
                zfree(*zp);
                power <<= 1;
        }
        if (zrel(z, *zp) >= 0)
                power++;
        if (power > 1)
                zfree(z);
        return power;
}


/*
 * Return the integral log base 10 of a number.
 *
 * If was_10_power != NULL, then this flag is set to true if the
 * value was a power of 10, false otherwise.
 */
long
zlog10(ZVALUE z, bool *was_10_power)
{
        ZVALUE *zp;                     /* current square */
        long power;                     /* current power */
        ZVALUE temp;                    /* temporary */
        ZVALUE pow10;                   /* power of 10 */
        FLAG rel;                       /* relationship */
        int i;

        /* NOTE: It is OK if was_10_power == NULL */

        if (ziszero(z)) {
                math_error("Zero argument argument for zlog10");
                not_reached();
        }

        /* Ignore sign of z */
        z.sign = 0;

        /* preload power10 table if missing */
        if (power10 == NULL) {
                long v;

                /* determine power10 table size */
                for (v=1, max_power10_exp=0;
                     v <= (long)(MAXLONG/10L);
                     v *= 10L, ++max_power10_exp) {
                }

                /* create power10 table */
                power10 = calloc(max_power10_exp+1, sizeof(long));
                if (power10 == NULL) {
                        math_error("cannot malloc power10 table");
                        not_reached();
                }

                /* load power10 table */
                for (i=0, v = 1L; i < max_power10_exp; ++i, v *= 10L) {
                        power10[i] = v;
                }
        }

        /* assume not a power of ten unless we find out otherwise */
        if (was_10_power != NULL) {
                *was_10_power = false;
        }

        /* quick exit for small values */
        if (! zgtmaxlong(z)) {
                long value = ztolong(z);

                for (i=0; i <= max_power10_exp; ++i) {
                        if (value == power10[i]) {
                                if (was_10_power != NULL) {
                                        *was_10_power = true;
                                }
                                return i;
                        } else if (value < power10[i]) {
                                return i-1;
                        }
                }
        }

        /*
         * Loop by squaring the base each time, and see whether or
         * not each successive square is still smaller than the number.
         */
        zp = &_tenpowers_[0];
        *zp = _ten_;
        while (((zp->len * 2) - 1) <= z.len) {  /* while square not too large */
                if (zp >= &_tenpowers_[TEN_MAX]) {
                        math_error("Maximum storable power of 10 reached!");
                        not_reached();
                }
                if (zp[1].len == 0)
                        zsquare(*zp, zp + 1);
                zp++;
        }

        /*
         * Now back down the squares, and multiply them together to see
         * exactly how many times the base can be raised by.
         */
        /* find the tenpower table entry < z */
        do {
                rel = zrel(*zp, z);
                if (rel == 0) {
                        /* quick return - we match a tenpower entry */
                        if (was_10_power != NULL) {
                                *was_10_power = true;
                        }
                        return (1L << (zp - _tenpowers_));
                }
        } while (rel > 0 && --zp >= _tenpowers_);
        if (zp < _tenpowers_) {
                math_error("fell off bottom of tenpower table!");
                not_reached();
        }

        /* the tenpower value is now our starting comparison value */
        zcopy(*zp, &pow10);
        power = (1L << (zp - _tenpowers_));

        /* try to build up a power of 10 from tenpower table entries */
        while (--zp >= _tenpowers_) {

                /* try the next lower tenpower value */
                zmul(pow10, *zp, &temp);
                rel = zrel(temp, z);
                if (rel == 0) {
                        /* exact power of 10 match */
                        power += (1L << (zp - _tenpowers_));
                        if (was_10_power != NULL) {
                                *was_10_power = true;
                        }
                        zfree(pow10);
                        zfree(temp);
                        return power;

                /* ignore this entry if we went too large */
                } else if (rel > 0) {
                        zfree(temp);

                /* otherwise increase power and keep going */
                } else {
                        power += (1L << (zp - _tenpowers_));
                        zfree(pow10);
                        pow10 = temp;
                }
        }
        zfree(pow10);
        return power;
}


/*
 * Return the number of times that one number will divide another.
 * This works similarly to zlog, except that divisions must be exact.
 * For example, zdivcount(540, 3) = 3, since 3^3 divides 540 but 3^4 won't.
 */
long
zdivcount(ZVALUE z1, ZVALUE z2)
{
        long count;             /* number of factors removed */
        ZVALUE tmp;             /* ignored return value */

        if (ziszero(z1) || ziszero(z2) || zisunit(z2))
                return 0;
        count = zfacrem(z1, z2, &tmp);
        zfree(tmp);
        return count;
}


/*
 * Remove all occurrences of the specified factor from a number.
 * Also returns the number of factors removed as a function return value.
 * Example:  zfacrem(540, 3, &x) returns 3 and sets x to 20.
 */
long
zfacrem(ZVALUE z1, ZVALUE z2, ZVALUE *rem)
{
        register ZVALUE *zp;            /* current square */
        long count;                     /* total count of divisions */
        long worth;                     /* worth of current square */
        long lowbit;                    /* for zlowbit(z2) */
        ZVALUE temp1, temp2, temp3;     /* temporaries */
        ZVALUE squares[32];             /* table of squares of factor */

        /* firewall */
        if (rem == NULL) {
                math_error("%s: rem NULL", __func__);
                not_reached();
        }

        z1.sign = 0;
        z2.sign = 0;
        /*
         * Reject trivial cases.
         */
        if ((z1.len < z2.len) || (zisodd(z1) && ziseven(z2)) ||
                ziszero(z2) || zisone(z2) ||
                ((z1.len == z2.len) && (z1.v[z1.len-1] < z2.v[z2.len-1]))) {
                rem->v = alloc(z1.len);
                rem->len = z1.len;
                rem->sign = 0;
                zcopyval(z1, *rem);
                return 0;
        }
        /*
         * Handle any power of two special.
         */
        if (zisonebit(z2)) {
                lowbit = zlowbit(z2);
                count = zlowbit(z1) / lowbit;
                rem->v = alloc(z1.len);
                rem->len = z1.len;
                rem->sign = 0;
                zcopyval(z1, *rem);
                zshiftr(*rem, count * lowbit);
                ztrim(rem);
                return count;
        }
        /*
         * See if the factor goes in even once.
         */
        zdiv(z1, z2, &temp1, &temp2, 0);
        if (!ziszero(temp2)) {
                zfree(temp1);
                zfree(temp2);
                rem->v = alloc(z1.len);
                rem->len = z1.len;
                rem->sign = 0;
                zcopyval(z1, *rem);
                return 0;
        }
        zfree(temp2);
        z1 = temp1;
        /*
         * Now loop by squaring the factor each time, and see whether
         * or not each successive square will still divide the number.
         */
        count = 1;
        worth = 1;
        zp = &squares[0];
        *zp = z2;
        while (((zp->len * 2) - 1) <= z1.len) { /* while square not too large */
                zsquare(*zp, &temp1);
                zdiv(z1, temp1, &temp2, &temp3, 0);
                if (!ziszero(temp3)) {
                        zfree(temp1);
                        zfree(temp2);
                        zfree(temp3);
                        break;
                }
                zfree(temp3);
                zfree(z1);
                z1 = temp2;
                *++zp = temp1;
                worth *= 2;
                count += worth;
        }

        /*
         * Now back down the list of squares, and see if the lower powers
         * will divide any more times.
         */
        /*
         * We prevent the zp pointer from walking behind squares
         * by stopping one short of the end and running the loop one
         * more time.
         *
         * We could stop the loop with just zp >= squares, but stopping
         * short and running the loop one last time manually helps make
         * code checkers such as insure happy.
         */
        for (; zp > squares; zp--, worth /= 2) {
                if (zp->len <= z1.len) {
                        zdiv(z1, *zp, &temp1, &temp2, 0);
                        if (ziszero(temp2)) {
                                temp3 = z1;
                                z1 = temp1;
                                temp1 = temp3;
                                count += worth;
                        }
                        zfree(temp1);
                        zfree(temp2);
                }
                if (zp != squares)
                        zfree(*zp);
        }
        /* run the loop manually one last time */
        if (zp == squares) {
                if (zp->len <= z1.len) {
                        zdiv(z1, *zp, &temp1, &temp2, 0);
                        if (ziszero(temp2)) {
                                temp3 = z1;
                                z1 = temp1;
                                temp1 = temp3;
                                count += worth;
                        }
                        zfree(temp1);
                        zfree(temp2);
                }
                if (zp != squares)
                        zfree(*zp);
        }

        *rem = z1;
        return count;
}


/*
 * Keep dividing a number by the gcd of it with another number until the
 * result is relatively prime to the second number.  Returns the number
 * of divisions made, and if this is positive, stores result at res.
 */
long
zgcdrem(ZVALUE z1, ZVALUE z2, ZVALUE *res)
{
        ZVALUE tmp1, tmp2, tmp3, tmp4;
        long count, onecount;
        long sh;

        /* firewall */
        if (res == NULL) {
                math_error("%s: res NULL", __func__);
                not_reached();
        }

        if (ziszero(z1) || ziszero(z2)) {
                math_error("Zero argument in call to zgcdrem!!!");
                not_reached();
        }
        /*
         * Begin by taking the gcd for the first time.
         * If the number is already relatively prime, then we are done.
         */
        z1.sign = 0;
        z2.sign = 0;
        if (zisone(z2))
                return 0;
        if (zisonebit(z2)) {
                sh = zlowbit(z1);
                if (sh == 0)
                        return 0;
                zshift(z1, -sh, res);
                return 1 + (sh - 1)/zlowbit(z2);
        }
        if (zisonebit(z1)) {
                if (zisodd(z2))
                        return 0;
                *res = _one_;
                return zlowbit(z1);
        }

        zgcd(z1, z2, &tmp1);
        if (zisunit(tmp1) || ziszero(tmp1)) {
                zfree(tmp1);
                return 0;
        }
        zequo(z1, tmp1, &tmp2);
        count = 1;
        z1 = tmp2;
        z2 = tmp1;
        /*
         * Now keep alternately taking the gcd and removing factors until
         * the gcd becomes one.
         */
        while (!zisunit(z2)) {
                onecount = zfacrem(z1, z2, &tmp3);
                if (onecount) {
                        count += onecount;
                        zfree(z1);
                        z1 = tmp3;
                } else {
                        zfree(tmp3);
                }
                zgcd(z1, z2, &tmp4);
                zfree(z2);
                z2 = tmp4;
        }
        zfree(z2);
        *res = z1;
        return count;
}


/*
 * Return the number of digits (base 10) in a number, ignoring the sign.
 */
long
zdigits(ZVALUE z1)
{
        long count, val;

        z1.sign = 0;
        if (!zge16b(z1)) {      /* do small numbers ourself */
                count = 1;
                val = 10;
                while (*z1.v >= (HALF)val) {
                        count++;
                        val *= 10;
                }
                return count;
        }
        return (zlog10(z1, NULL) + 1);
}


/*
 * Return the single digit at the specified decimal place of a number,
 * where 0 means the rightmost digit.  Example:  zdigit(1234, 1) = 3.
 */
long
zdigit(ZVALUE z1, long n)
{
        ZVALUE tmp1, tmp2;
        long res;

        z1.sign = 0;
        if (ziszero(z1) || (n < 0) || (n / BASEDIG >= z1.len))
                return 0;
        if (n == 0)
                return zmodi(z1, 10L);
        if (n == 1)
                return zmodi(z1, 100L) / 10;
        if (n == 2)
                return zmodi(z1, 1000L) / 100;
        if (n == 3)
                return zmodi(z1, 10000L) / 1000;
        ztenpow(n, &tmp1);
        zquo(z1, tmp1, &tmp2, 0);
        res = zmodi(tmp2, 10L);
        zfree(tmp1);
        zfree(tmp2);
        return res;
}


/*
 * z is to be a nonnegative integer
 * If z is the square of a integer stores at dest the square root of z;
 *      otherwise stores at z an integer differing from the square root
 *      by less than 1.  Returns the sign of the true square root minus
 *      the calculated integer.  Type of rounding is determined by
 *      rnd as follows: rnd = 0 gives round down, rnd = 1
 *      rounds up, rnd = 8 rounds to even integer, rnd = 9 rounds to odd
 *      integer, rnd = 16 rounds to nearest integer.
 */
FLAG
zsqrt(ZVALUE z, ZVALUE *dest, long rnd)
{
        HALF *a, *A, *b, *a0, u;
        int i, j, j1, j2, k, k1, m, m0, m1, n, n0, o;
        FULL d, e, f, g, h, s, t, x, topbit;
        int remsign;
        bool up, onebit;
        ZVALUE sqrt;

        /* firewall */
        if (dest == NULL) {
                math_error("%s: dest NULL", __func__);
                not_reached();
        }

        if (z.sign) {
                math_error("Square root of negative number");
                not_reached();
        }
        if (ziszero(z)) {
                *dest = _zero_;
                return 0;
        }
        m0 = z.len;
        o = m0 & 1;
        m = m0 + o;             /* m is smallest even number >= z.len */
        n0 = n = m / 2;
        f = z.v[z.len - 1];
        k = 1;
        while (f >>= 2)
                k++;
        if (!o)
                k += BASEB/2;
        j = BASEB - k;
        m1 = m;
        if (k == BASEB) {
                m1 += 2;
                n0++;
        }
        A = alloc(m1);
        A[m1] = 0;
        a0 = A + n0;
        memcpy(A, z.v, m0 * sizeof(HALF));
        if (o)
                A[m - 1] = 0;
        if (n == 1) {
                if (j)
                        f = (FULL) A[1] << j | A[0] >> k;
                else
                        f = A[1];
                g = (FULL) A[0] << (j + BASEB);
                d = e = topbit = (FULL)1 << (k - 1);
        } else {
                if (j)
                        f = (FULL) A[m-1] << (j + BASEB) | (FULL) A[m-2] << j |
                                A[m-3] >> k;
                else
                        f = (FULL) A[m-1] << BASEB | A[m-2];
                g = (FULL) A[m-3] << (j + BASEB) | (FULL) A[m-4] << j;
                d = e = topbit = (FULL)1 << (BASEB + k - 1);
        }

        s = (f & topbit);
        f <<= 1;
        if (g & TOPFULL)
                f++;
        g <<= 1;
        if (s) {
                f -= 4 * d;
                e = 2 * d - 1;
        }
        else
                f -= d;
        while (d >>= 1) {
                if (!(s | f | g))
                        break;
                while (d && (f & topbit) == s) {
                        d >>= 1;
                        f <<= 1;
                        if (g & TOPFULL)
                                f++;
                        g <<= 1;
                }
                if (d == 0)
                        break;
                if (s)
                        f += e + 1;
                else
                        f -= e;
                t = f & topbit;
                f <<= 1;
                if (g & TOPFULL)
                        f++;
                g <<= 1;
                if (t == 0 && f < d)
                        t = topbit;
                f -= d;
                if (s)
                        e -= d - !t;
                else
                        e += d - (t > 0);
                s = t;
        }
        if (n0 == 1) {
                A[1] = (HALF)e;
                A[0] = (HALF)f;
                m = 1;
                goto done;
        }
        if (n0 == 2) {
                A[3] = (HALF)(e >> BASEB);
                A[2] = (HALF)e;
                A[1] = (HALF)(f >> BASEB);
                A[0] = (HALF)f;
                m = 2;
                goto done;
        }
        u = (HALF)(s ? BASE1 : 0);
        if (k < BASEB) {
                A[m1 - 1] = (HALF)(e >> (BASEB - 1));
                A[m1 - 2] = ((HALF)(e << 1) | (HALF)(s > 0));
                A[m1 - 3] = (HALF)(f >> BASEB);
                A[m1 - 4] = (HALF)f;
                m = m1 - 2;
                k1 = k + 1;
        } else {
                A[m1 - 1] = 1;
                A[m1 - 2] = (HALF)(e >> (BASEB - 1));
                A[m1 - 3] = ((HALF)(e << 1) | (HALF)(s > 0));
                A[m1 - 4] = u;
                A[m1 - 5] = (HALF)(f >> BASEB);
                A[m1 - 6] = (HALF)f;
                m = m1 - 3;
                k1 = 1;
        }
        h = e >> k;
        onebit = ((e & ((FULL)1 << (k - 1))) ? true : false);
        j2 = BASEB - k1;
        j1 = BASEB + j2;
        while (m > n0) {
                a = A + m - 1;
                if (j2)
                        f = (FULL) *a << j1 | (FULL) a[-1] << j2 | a[-2] >> k1;
                else
                        f = (FULL) *a << BASEB | a[-1];
                if (u)
                        f = ~f;
                x = f / h;
                if (x) {
                        if (onebit && x > 2 * (f % h) + 2)
                                x--;
                        b = a + 1;
                        i = m1 - m;
                        a -= i + 1;
                        if (u) {
                                f = *a + x * (BASE - x);
                                *a++ = (HALF)f;
                                u = (HALF)(f >> BASEB);
                                while (i--) {
                                        f = *a + x * *b++ + u;
                                        *a++ = (HALF)f;
                                        u = (HALF)(f >> BASEB);
                                }
                                u += *a;
                                x = ~x + !u;
                                if (!(x & TOPHALF))
                                        a[1] -= 1;
                        } else {
                                f = *a - x * x;
                                *a++ = (HALF)f;
                                u = -(HALF)(f >> BASEB);
                                while (i--) {
                                        f = *a - x * *b++ - u;
                                        *a++ = (HALF)f;
                                        u = -(HALF)(f >> BASEB);
                                }
                                u = *a - u;
                                x = x + u;
                                if (x & TOPHALF)
                                        a[1] |= 1;
                        }
                        *a = ((HALF)(x << 1) | (HALF)(u > 0));
                } else {
                        *a = u;
                }
                m--;
                if (*--a == u) {
                        while (m > 1 && *--a == u)
                                m--;
                }
        }
        i = n;
        a = a0;
        while (i--) {
                *a >>= 1;
                if (a[1] & 1) *a |= TOPHALF;
                a++;
        }
        s = u;
done:   if (s == 0) {
                while (m > 0 && A[m - 1] == 0)
                        m--;
                if (m == 0) {
                        remsign = 0;
                        sqrt.v = alloc(n);
                        sqrt.len = n;
                        sqrt.sign = 0;
                        memcpy(sqrt.v, a0, n * sizeof(HALF));
                        freeh(A);
                        *dest = sqrt;
                        return remsign;
                }
        }
        if (rnd & 16) {
                if (s == 0) {
                        if (m != n) {
                                up = (m > n);
                        } else {
                                i = n;
                                b = a0 + n;
                                a = A + n;
                                while (i > 0 && *--a == *--b)
                                        i--;
                                up = (i > 0 && *a > *b);
                        }
                } else {
                        while (m > 1 && A[m - 1] == BASE1)
                                m--;
                        if (m != n) {
                                up = (m < n);
                        } else {
                                i = n;
                                b = a0 + n;
                                a = A + n;
                                while (i > 0 && *--a + *--b == BASE1)
                                        i--;
                                up = ((FULL) *a + *b >= BASE);
                        }
                }
        }
        else
        if (rnd & 8)
                up = (((rnd ^ *a0) & 1) ? true : false);
        else
                up = ((rnd & 1) ? true : false);
        if (up) {
                remsign = -1;
                i = n;
                a = a0;
                while (i-- && *a == BASE1)
                        *a++ = 0;
                if (i >= 0) {
                        (*a)++;
                } else {
                        n++;
                        *a = 1;
                }
        } else {
                remsign = 1;
        }
        sqrt.v = alloc(n);
        sqrt.len = n;
        sqrt.sign = 0;
        memcpy(sqrt.v, a0, n * sizeof(HALF));
        freeh(A);
        *dest = sqrt;
        return remsign;

}

/*
 * Take an arbitrary root of a number (to the greatest integer).
 * This uses the following iteration to get the K-th root of N:
 *      x = ((K-1) * x + N / x^(K-1)) / K
 */
void
zroot(ZVALUE z1, ZVALUE z2, ZVALUE *dest)
{
        ZVALUE ztry, quo, old, temp, temp2;
        ZVALUE k1;                      /* holds k - 1 */
        int sign;
        long i;
        LEN highbit, k;
        SIUNION sival;

        /* firewall */
        if (dest == NULL) {
                math_error("%s: dest NULL", __func__);
                not_reached();
        }

        sign = z1.sign;
        if (sign && ziseven(z2)) {
                math_error("Even root of negative number");
                not_reached();
        }
        if (ziszero(z2) || zisneg(z2)) {
                math_error("Non-positive root");
                not_reached();
        }
        if (ziszero(z1)) {      /* root of zero */
                *dest = _zero_;
                return;
        }
        if (zisunit(z2)) {      /* first root */
                zcopy(z1, dest);
                return;
        }
        if (zge31b(z2)) {       /* humongous root */
                *dest = _one_;
                dest->sign = (bool)((HALF)sign);
                return;
        }
        k = (LEN)ztolong(z2);
        highbit = zhighbit(z1);
        if (highbit < k) {      /* too high a root */
                *dest = _one_;
                dest->sign = (bool)((HALF)sign);
                return;
        }
        sival.ivalue = k - 1;
        k1.v = &sival.silow;
        /* ignore Saber-C warning #112 - get ushort from uint */
        /*        OK to ignore on name zroot`sival */
        k1.len = 1 + (sival.sihigh != 0);
        k1.sign = 0;
        z1.sign = 0;
        /*
         * Allocate the numbers to use for the main loop.
         * The size and high bits of the final result are correctly set here.
         * Notice that the remainder of the test value is rubbish, but this
         * is unimportant.
         */
        highbit = (highbit + k - 1) / k;
        ztry.len = (highbit / BASEB) + 1;
        ztry.v = alloc(ztry.len);
        zclearval(ztry);
        ztry.v[ztry.len-1] = ((HALF)1 << (highbit % BASEB));
        ztry.sign = 0;
        old.v = alloc(ztry.len);
        old.len = 1;
        zclearval(old);
        old.sign = 0;
        /*
         * Main divide and average loop
         */
        for (;;) {
                zpowi(ztry, k1, &temp);
                zquo(z1, temp, &quo, 0);
                zfree(temp);
                i = zrel(ztry, quo);
                if (i <= 0) {
                        /*
                         * Current try is less than or equal to the root since
                         * it is less than the quotient. If the quotient is
                         * equal to the try, we are all done.  Also, if the
                         * try is equal to the old value, we are done since
                         * no improvement occurred.  If not, save the improved
                         * value and loop some more.
                         */
                        if ((i == 0) || (zcmp(old, ztry) == 0)) {
                                zfree(quo);
                                zfree(old);
                                ztry.sign = (bool)((HALF)sign);
                                zquicktrim(ztry);
                                *dest = ztry;
                                return;
                        }
                        old.len = ztry.len;
                        zcopyval(ztry, old);
                }
                /* average current try and quotient for the new try */
                zmul(ztry, k1, &temp);
                zfree(ztry);
                zadd(quo, temp, &temp2);
                zfree(temp);
                zfree(quo);
                zquo(temp2, z2, &ztry, 0);
                zfree(temp2);
        }
}


/*
 * Test to see if a number is an exact square or not.
 */
bool
zissquare(ZVALUE z)
{
        long n;
        ZVALUE tmp;

        /* negative values are never perfect squares */
        if (zisneg(z)) {
                return false;
        }

        /* ignore trailing zero words */
        while ((z.len > 1) && (*z.v == 0)) {
                z.len--;
                z.v++;
        }

        /* zero or one is a perfect square */
        if (zisabsleone(z)) {
                return true;
        }

        /* check mod 4096 values */
        if (issq_mod4k[(int)(*z.v & 0xfff)] == 0) {
                return false;
        }

        /* must do full square root test now */
        n = !zsqrt(z, &tmp, 0);
        zfree(tmp);
        return (n ? true : false);
}


/*
 * test if a number is an integer power of 2
 *
 * given:
 *      z       value to check if it is a power of 2
 *      log2    when z is an integer power of 2 (true return), *log2 is set to log base 2 of z
 *              when z is NOT an integer power of 2 (false return), *log2 is not touched
 *
 * returns:
 *      true    z is a power of 2
 *      false   z is not a power of 2
 */
bool
zispowerof2(ZVALUE z, FULL *log2)
{
        FULL ilogz;             /* potential log base 2 return value or -1 */
        HALF tophalf;           /* most significant HALF in z */
        LEN len;                /* length of z in HALFs */
        int i;

        /* firewall */
        if (log2 == NULL) {
                math_error("%s: log2 NULL", __func__);
                not_reached();
        }

        /* zero and negative values are never integer powers of 2 */
        if (ziszero(z) || zisneg(z)) {
                return false;
        }

        /*
         * trim z just in case
         *
         * An untrimmed z will give incorrect results.
         */
        ztrim(&z);

        /*
         * all HALFs below the top HALF must be zero
         */
        len = z.len;
        for (i=0, ilogz=0; i < len-1; ++i, ilogz+=BASEB) {
                if (z.v[i] != 0) {
                        return false;
                }
        }

        /*
         * top HALF must be a power of 2
         *
         * For non-zero values of tophalf,
         * (tophalf & (tophalf-1)) == 0 ==> tophalf is a power of 2,
         * (tophalf & (tophalf-1)) != 0 ==> tophalf is NOT a power of 2.
         */
        tophalf = z.v[len-1];
        if ((tophalf == 0) || ((tophalf & (tophalf-1)) != 0)) {
                return false;
        }

        /*
         * count the bits in the top HALF which is a power of 2
         */
        for (i=0; i < BASEB && tophalf != ((HALF)1 << i); ++i) {
                ++ilogz;
        }

        /*
         * return power of 2
         */
        *log2 = ilogz;
        return true;
}
