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/*******************************************************************************
* Copyright (c) 2004 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Common Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/cpl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.debug.core.model;
/**
* A byte of memory in a meomry block. Each byte of memory has a value and
* attributes indicating if the byte is read-only, valid, or if its value has
* changed.
* <p>
* Clients may subclass this class.
* TODO: when would a client subclass this class?
* </p>
* @since 3.1
*/
public abstract class MemoryByte {
/**
* Bit mask used to indicate a byte is read-only.
*/
public static final byte READONLY = 0x01;
/**
* Bit mask used to indicate a byte is valid.
*
* TODO: specify what makes a byte valid - when is a byte invalid?
*/
public static final byte VALID = 0x02;
/**
* Bit mask used to indicate a byte has changed.
*
* TODO: specify CHANGE flag more clearly - changed since when?
*/
public static final byte CHANGED = 0x04;
/**
* Bit mask used to indicate a byte has no history to
* determine if the byte is changed or not. The change bit has
* no meaning if this bit is on.
*/
public static final byte UNKNOWN = 0x08;
/**
* Value of this byte.
*/
protected byte value;
/**
* Attribute flags.
* <p>
* To specify VALID: flags |= MemoryByte.VALID;
* To specify READONLY: flags |= MemoryByte.READONLY;
* </p>
*/
protected byte flags;
/**
* Constructs a read-write, invalid, unchanged memory byte with a
* value of 0.
*
* TODO: should the valid flag be set for convenience?
*/
public MemoryByte() {
}
/**
* Constructs a read-write, invalid, unchanged memory byte with
* the given value.
*
* @param byteValue value of this memory byte
*
* TODO: should the valid flag be set for convenience?
*/
public MemoryByte(byte byteValue) {
value = byteValue;
}
/**
* Constructs a memory byte with the given value and attributes.
*
* @param byteValue value of this memory byte
* @param byteFlags attributes of the byte specified as a bit mask
*/
public MemoryByte(byte byteValue, byte byteFlags) {
value = byteValue;
flags = byteFlags;
}
/**
* Returns this memory byte's attribute as a bit mask.
*
* @return this memory byte's attribute as a bit mask
*/
public byte getFlags() {
return flags;
}
/**
* Sets this memory byte's attributes based on the given bit mask.
*
* @param flags bit mask of attributes
*/
public void setFlags(byte flags) {
this.flags = flags;
}
/**
* Returns the value of this memory byte.
*
* @return the value of this memory byte
*/
public byte getValue() {
return value;
}
/**
* Sets the value of this memory byte.
*
* @param value the new value of this memory byte
*/
public void setValue(byte value) {
this.value = value;
}
/**
* Sets whether this memory byte is valid.
*
* @param valid whether this memory byte is valid
*/
public void setValid(boolean valid) {
flags |= MemoryByte.VALID;
if (!valid)
flags ^= MemoryByte.VALID;
}
/**
* Returns whether this memory byte is valid.
*
* @return whether this memory byte is valid
*/
public boolean isValid() {
return ((flags & MemoryByte.VALID) == MemoryByte.VALID);
}
/**
* Sets whether this memory byte is read-only.
*
* @param readonly whether this memory byte is read-only.
*/
public void setReadonly(boolean readonly) {
flags |= MemoryByte.READONLY;
if (!readonly)
flags ^= MemoryByte.READONLY;
}
/**
* Returns whether this memory byte is read-only.
*
* @return whether this memory byte is read-only
*/
public boolean isReadonly() {
return ((flags & MemoryByte.READONLY) == MemoryByte.READONLY);
}
/**
* Sets whether this memory byte has changed.
*
* @param changed whether this memory byte has changed
*/
public void setChanged(boolean changed) {
flags |= MemoryByte.CHANGED;
if (!changed)
flags ^= MemoryByte.CHANGED;
}
/**
* Returns whether this memory byte has changed.
*
* @return whether this memory byte has changed
*/
public boolean isChanged() {
return ((flags & MemoryByte.CHANGED) == MemoryByte.CHANGED);
}
/**
* Sets whether the value of this byte is unknown. When a value
* is unknown, the change state of a memory byte has no meaning.
*
* TODO: this flag should be changed to the 'positive' KNOWN rather than
* the 'negative' UNKNOWN. All other flags read in the positive state:
* is valid, is read-only, is changed. Similarly, this flag should read
* as is known.
*
* @param unknown whether the value of this byte is unknown
*/
public void setUnknown(boolean unknown) {
flags |= MemoryByte.UNKNOWN;
if (!unknown)
flags ^= MemoryByte.UNKNOWN;
}
/**
* Returns whether the value of this byte is unknown. When a value
* is unknown, the change state of a memory byte has no meaning.
*
* @return whether the value of this byte is unknown
*/
public boolean isUnknown() {
return ((flags & MemoryByte.UNKNOWN) == MemoryByte.UNKNOWN);
}
}
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