1 /*
   2  *  Copyright (c) 2019, 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.  Oracle designates this
   8  *  particular file as subject to the "Classpath" exception as provided
   9  *  by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  *  This code is distributed in the hope that it will be useful, but WITHOUT
  12  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  *  version 2 for more details (a copy is included in the LICENSE file that
  15  *  accompanied this code).
  16  *
  17  *  You should have received a copy of the GNU General Public License version
  18  *  2 along with this work; if not, write to the Free Software Foundation,
  19  *  Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  *   Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  *  or visit www.oracle.com if you need additional information or have any
  23  *  questions.
  24  *
  25  */
  26 package jdk.incubator.foreign;
  27 
  28 import java.lang.constant.ConstantDescs;
  29 import java.lang.constant.DynamicConstantDesc;
  30 import java.util.Objects;
  31 import java.util.Optional;
  32 import java.util.OptionalLong;
  33 
  34 /**
  35  * A padding layout. A padding layout specifies the size of extra space which is typically not accessed by applications,
  36  * and is typically used for aligning member layouts around word boundaries.
  37  * <p>
  38  * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
  39  * class; use of identity-sensitive operations (including reference equality
  40  * ({@code ==}), identity hash code, or synchronization) on instances of
  41  * {@code PaddingLayout} may have unpredictable results and should be avoided.
  42  * The {@code equals} method should be used for comparisons.
  43  *
  44  * @implSpec
  45  * This class is immutable and thread-safe.
  46  */
  47 /* package-private */ final class PaddingLayout extends AbstractLayout implements MemoryLayout {
  48 
  49     PaddingLayout(long size) {
  50         this(size, size, Optional.empty());
  51     }
  52 
  53     PaddingLayout(long size, long alignment, Optional<String> name) {
  54         super(OptionalLong.of(size), alignment, name);
  55     }
  56 
  57     @Override
  58     public String toString() {
  59         return decorateLayoutString("x" + bitSize());
  60     }
  61 
  62     @Override
  63     public boolean equals(Object other) {
  64         if (this == other) {
  65             return true;
  66         }
  67         if (!super.equals(other)) {
  68             return false;
  69         }
  70         if (!(other instanceof PaddingLayout)) {
  71             return false;
  72         }
  73         PaddingLayout p = (PaddingLayout)other;
  74         return bitSize() == p.bitSize();
  75     }
  76 
  77     @Override
  78     public int hashCode() {
  79         return Objects.hash(super.hashCode(), bitSize());
  80     }
  81 
  82     @Override
  83     PaddingLayout dup(long alignment, Optional<String> name) {
  84         return new PaddingLayout(bitSize(), alignment, name);
  85     }
  86 
  87     @Override
  88     public Optional<DynamicConstantDesc<MemoryLayout>> describeConstable() {
  89         return Optional.of(DynamicConstantDesc.ofNamed(ConstantDescs.BSM_INVOKE, "padding",
  90                 CD_LAYOUT, MH_PADDING, bitSize()));
  91     }
  92 
  93     //hack: the declarations below are to make javadoc happy; we could have used generics in AbstractLayout
  94     //but that causes issues with javadoc, see JDK-8224052
  95 
  96     /**
  97      * {@inheritDoc}
  98      */
  99     @Override
 100     public PaddingLayout withName(String name) {
 101         return (PaddingLayout)super.withName(name);
 102     }
 103 
 104     /**
 105      * {@inheritDoc}
 106      */
 107     @Override
 108     public PaddingLayout withBitAlignment(long alignmentBits) {
 109         return (PaddingLayout)super.withBitAlignment(alignmentBits);
 110     }
 111 }