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Common Lisp implementation running on the JVM

There is a newer version: 1.9.2

/*
 * logcount.java
 *
 * Copyright (C) 2003-2005 Peter Graves
 * $Id$
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obligated to do so.  If you do not wish to do so, delete this
 * exception statement from your version.
 */

package org.armedbear.lisp;

import static org.armedbear.lisp.Lisp.*;

import java.math.BigInteger;

// ### logcount integer => number-of-on-bits
public final class logcount extends Primitive
{
    private logcount()
    {
        super("logcount","integer");
    }

    @Override
    public LispObject execute(LispObject arg)
    {
        int n;
        if (arg instanceof Fixnum) {
            int value = ((Fixnum)arg).value;
            n = Integer.bitCount(value < 0 ? ~value : value);
        } else if (arg instanceof Bignum)
            n = ((Bignum)arg).value.bitCount();
        else
            return type_error(arg, Symbol.INTEGER);
        return Fixnum.getInstance(n);
    }

    private static final Primitive LOGCOUNT = new logcount();
}