package org.exist.util;
import java.io.Writer;
/**
* This class provides a compressed representation of a sequence of whitespace characters. The representation
* is a sequence of bytes: in each byte the top two bits indicate which whitespace character is used
* (x9, xA, xD, or x20) and the bottom six bits indicate the number of such characters. A zero byte is a filler.
* We don't compress the sequence if it would occupy more than 8 bytes, because that's the space we've got available
* in the TinyTree arrays.
*/
public class CompressedWhitespace implements CharSequence {
private static char[] WHITE_CHARS = {0x09, 0x0A, 0x0D, 0x20};
private long value;
public CompressedWhitespace(long compressedValue) {
this.value = compressedValue;
}
/**
* Attempt to compress a CharSequence
* @param in the CharSequence to be compressed
* @return the compressed sequence if it can be compressed; or the original CharSequence otherwise
*/
public static CharSequence compress(CharSequence in) {
final int inlen = in.length();
if (inlen == 0) {
return in;
}
int runlength = 1;
int outlength = 0;
for (int i=0; i<inlen; i++) {
final char c = in.charAt(i);
if (("\t\n\r ").indexOf(c) >= 0) {
if (i == inlen-1 || c != in.charAt(i+1) || runlength == 63) {
runlength = 1;
outlength++;
if (outlength > 8) {
return in;
}
} else {
runlength++;
}
} else {
return in;
}
}
int ix = 0;
runlength = 1;
int[] out = new int[outlength];
for (int i=0; i<inlen; i++) {
final char c = in.charAt(i);
if (i == inlen-1 || c != in.charAt(i+1) || runlength == 63) {
int code = ("\t\n\r ").indexOf(c);
out[ix++] = (code<<6) | runlength;
runlength = 1;
} else {
runlength++;
}
}
long value = 0;
for (int i=0; i<outlength; i++) {
value = (value<<8) | out[i];
}
for (int i=0; i<(8-outlength); i++) {
value = (value<<8);
}
return new CompressedWhitespace(value);
}
/**
* Uncompress the whitespace to a FastStringBuffer
* @param buffer the buffer to which the whitespace is to be appended. The parameter may be
* null, in which case a new buffer is created.
* @return the FastStringBuffer to which the whitespace has been appended. If a buffer was
* supplied in the argument, this will be the same buffer.
*/
public FastStringBuffer uncompress(FastStringBuffer buffer) {
if (buffer == null) {
buffer = new FastStringBuffer(length());
}
final long val = value;
for (int s=56; s>=0; s-=8) {
byte b = (byte)((val>>>s) & 0xff);
if (b == 0) {
break;
}
char c = WHITE_CHARS[b>>>6 & 0x3];
int len = (b & 0x3f);
for (int j=0; j<len; j++) {
buffer.append(c);
}
}
return buffer;
}
public long getCompressedValue() {
return value;
}
public int length() {
int count = 0;
long val = value;
for (int s=56; s>=0; s-=8) {
int c = (int)((val>>>s) & 0x3f);
if (c == 0) {
break;
}
count += c;
}
return count;
}
/**
* Returns the <code>char</code> value at the specified index. An index ranges from zero
* to <tt>length() - 1</tt>. The first <code>char</code> value of the sequence is at
* index zero, the next at index one, and so on, as for array
* indexing. </p>
* <p/>
* <p>If the <code>char</code> value specified by the index is a
* <a href="Character.html#unicode">surrogate</a>, the surrogate
* value is returned.
*
* @param index the index of the <code>char</code> value to be returned
* @return the specified <code>char</code> value
* @throws IndexOutOfBoundsException if the <tt>index</tt> argument is negative or not less than
* <tt>length()</tt>
*/
public char charAt(int index) {
int count = 0;
final long val = value;
for (int s=56; s>=0; s-=8) {
byte b = (byte)((val>>>s) & 0xff);
if (b == 0) {
break;
}
count += (b & 0x3f);
if (count > index) {
return WHITE_CHARS[b>>>6 & 0x3];
}
}
throw new IndexOutOfBoundsException(index+"");
}
/**
* Returns a new <code>CharSequence</code> that is a subsequence of this sequence.
* The subsequence starts with the <code>char</code> value at the specified index and
* ends with the <code>char</code> value at index <tt>end - 1</tt>. The length
* (in <code>char</code>s) of the
* returned sequence is <tt>end - start</tt>, so if <tt>start == end</tt>
* then an empty sequence is returned. </p>
*
* @param start the start index, inclusive
* @param end the end index, exclusive
* @return the specified subsequence
* @throws IndexOutOfBoundsException if <tt>start</tt> or <tt>end</tt> are negative,
* if <tt>end</tt> is greater than <tt>length()</tt>,
* or if <tt>start</tt> is greater than <tt>end</tt>
*/
public CharSequence subSequence(int start, int end) {
return uncompress(null).subSequence(start, end);
}
/**
* Indicates whether some other object is "equal to" this one.
*/
public boolean equals(Object obj) {
if (obj instanceof CompressedWhitespace) {
return value == ((CompressedWhitespace)obj).value;
}
return uncompress(null).equals(obj);
}
/**
* Returns a hash code value for the object.
*/
public int hashCode() {
return uncompress(null).hashCode();
}
/**
* Returns a string representation of the object.
*/
public String toString() {
return uncompress(null).toString();
}
/**
* Write the value to a Writer
*/
public void write(Writer writer) throws java.io.IOException {
final long val = value;
for (int s=56; s>=0; s-=8) {
final byte b = (byte)((val>>>s) & 0xff);
if (b == 0) {
break;
}
final char c = WHITE_CHARS[b>>>6 & 0x3];
final int len = (b & 0x3f);
for (int j=0; j<len; j++) {
writer.write(c);
}
}
}
/**
* Write the value to a Writer with escaping of special characters
*/
public void writeEscape(boolean[] specialChars, Writer writer) throws java.io.IOException {
final long val = value;
for (int s=56; s>=0; s-=8) {
final byte b = (byte)((val>>>s) & 0xff);
if (b == 0) {
break;
}
final char c = WHITE_CHARS[b>>>6 & 0x3];
final int len = (b & 0x3f);
if (specialChars[c]) {
String e = "";
if (c=='\n') {
e = "
";
} else if (c=='\r') {
e = "
";
} else if (c=='\t') {
e = " ";
}
for (int j=0; j<len; j++) {
writer.write(e);
}
} else {
for (int j=0; j<len; j++) {
writer.write(c);
}
}
}
}
public static void main( String[] args ) {
CharSequence c = compress("\t\n\n\t\t\n ");
System.err.println(c);
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none
//