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 }