1 /* 2 * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package jdk.vm.ci.meta; 24 25 /** 26 * Represents a logic value that can be either {@link #TRUE}, {@link #FALSE}, or {@link #UNKNOWN}. 27 */ 28 public enum TriState { 29 TRUE, 30 FALSE, 31 UNKNOWN; 32 33 public static TriState get(boolean value) { 34 return value ? TRUE : FALSE; 35 } 36 37 /** 38 * This is optimistic about {@link #UNKNOWN} (it prefers known values over {@link #UNKNOWN}) and 39 * pesimistic about known (it perfers {@link #TRUE} over {@link #FALSE}). 40 */ 41 public static TriState merge(TriState a, TriState b) { 42 if (a == TRUE || b == TRUE) { 43 return TRUE; 44 } 45 if (a == FALSE || b == FALSE) { 46 return FALSE; 47 } 48 assert a == UNKNOWN && b == UNKNOWN; 49 return UNKNOWN; 50 } 51 52 public boolean isTrue() { 53 return this == TRUE; 54 } 55 56 public boolean isFalse() { 57 return this == FALSE; 58 } 59 60 public boolean isUnknown() { 61 return this == UNKNOWN; 62 } 63 64 public boolean isKnown() { 65 return this != UNKNOWN; 66 } 67 68 public boolean toBoolean() { 69 if (isTrue()) { 70 return true; 71 } else if (isFalse()) { 72 return false; 73 } else { 74 throw new IllegalStateException("Cannot convert to boolean, TriState is in an unknown state"); 75 } 76 } 77 }