001/*
002 * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation.
008 *
009 * This code is distributed in the hope that it will be useful, but WITHOUT
010 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
011 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
012 * version 2 for more details (a copy is included in the LICENSE file that
013 * accompanied this code).
014 *
015 * You should have received a copy of the GNU General Public License version
016 * 2 along with this work; if not, write to the Free Software Foundation,
017 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
018 *
019 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
020 * or visit www.oracle.com if you need additional information or have any
021 * questions.
022 */
023package jdk.internal.jvmci.meta;
024
025/**
026 * Represents a logic value that can be either {@link #TRUE}, {@link #FALSE}, or {@link #UNKNOWN}.
027 */
028public enum TriState {
029    TRUE,
030    FALSE,
031    UNKNOWN;
032
033    public static TriState get(boolean value) {
034        return value ? TRUE : FALSE;
035    }
036
037    /**
038     * This is optimistic about {@link #UNKNOWN} (it prefers known values over {@link #UNKNOWN}) and
039     * pesimistic about known (it perfers {@link #TRUE} over {@link #FALSE}).
040     */
041    public static TriState merge(TriState a, TriState b) {
042        if (a == TRUE || b == TRUE) {
043            return TRUE;
044        }
045        if (a == FALSE || b == FALSE) {
046            return FALSE;
047        }
048        assert a == UNKNOWN && b == UNKNOWN;
049        return UNKNOWN;
050    }
051
052    public boolean isTrue() {
053        return this == TRUE;
054    }
055
056    public boolean isFalse() {
057        return this == FALSE;
058    }
059
060    public boolean isUnknown() {
061        return this == UNKNOWN;
062    }
063
064    public boolean isKnown() {
065        return this != UNKNOWN;
066    }
067
068    public boolean toBoolean() {
069        if (isTrue()) {
070            return true;
071        } else if (isFalse()) {
072            return false;
073        } else {
074            throw new IllegalStateException("Cannot convert to boolean, TriState is in an unknown state");
075        }
076    }
077}