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TMI-TIFF: Faster LZW encoder.
This commit is contained in:
Harald Kuhr
parent
051a1dcb5b
commit
1a8948ece9
@ -33,21 +33,22 @@ import com.twelvemonkeys.io.enc.Encoder;
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import java.io.IOException;
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import java.io.OutputStream;
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import java.nio.ByteBuffer;
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import java.util.Map;
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import java.util.TreeMap;
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import static com.twelvemonkeys.imageio.plugins.tiff.LZWDecoder.LZWString;
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import java.util.Arrays;
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/**
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* LZWEncoder
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* <p/>
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* Inspired by LZWTreeEncoder by <a href="mailto:yuwen_66@yahoo.com">Wen Yu</a> and the
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* <a href="http://gingko.homeip.net/docs/file_formats/lzwgif.html#bob">algorithm described by Bob Montgomery</a>
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* which
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* "[...] uses a tree method to search if a new string is already in the table,
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* which is much simpler, faster, and easier to understand than hashing."
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*
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* @author <a href="mailto:harald.kuhr@gmail.com">Harald Kuhr</a>
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* @author last modified by $Author: haraldk$
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* @version $Id: LZWEncoder.java,v 1.0 02.12.13 14:13 haraldk Exp$
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*/
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final class LZWEncoder implements Encoder {
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// TODO: Consider extracting LZWStringTable from LZWDecoder
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/** Clear: Re-initialize tables. */
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static final int CLEAR_CODE = 256;
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/** End of Information. */
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@ -58,16 +59,18 @@ final class LZWEncoder implements Encoder {
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private static final int TABLE_SIZE = 1 << MAX_BITS;
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private final LZWString[] table = new LZWString[TABLE_SIZE];
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private final Map<LZWString, Integer> reverseTable = new TreeMap<>(); // This is foobar
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// private final Map<LZWString, Integer> reverseTable = new HashMap<>(TABLE_SIZE); // This is foobar
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private int tableLength;
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LZWString omega = LZWString.EMPTY;
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// A child is made up of a parent (or prefix) code plus a suffix byte
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// and siblings are strings with a common parent(or prefix) and different
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// suffix bytes
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private final short[] CHILDREN = new short[TABLE_SIZE];
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private final short[] SIBLINGS = new short[TABLE_SIZE];
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private final short[] SUFFIXES = new short[TABLE_SIZE];
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int bitsPerCode;
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private int oldCode = CLEAR_CODE;
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private int maxCode;
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int bitMask;
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// Initial setup
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private int parent = -1;
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private int bitsPerCode = MIN_BITS;
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private int nextValidCode = EOI_CODE + 1;
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private int maxCode = maxValue(bitsPerCode);
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// Buffer for partial codes
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private int bits = 0;
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@ -76,120 +79,116 @@ final class LZWEncoder implements Encoder {
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// Keep track of how many bytes we will write, to make sure we write EOI at correct position
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private long remaining;
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protected LZWEncoder(final int length) {
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this.remaining = length;
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// First 258 entries of table is always fixed
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for (int i = 0; i < 256; i++) {
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table[i] = new LZWString((byte) i);
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}
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init();
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}
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private void init() {
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tableLength = 258;
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bitsPerCode = MIN_BITS;
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bitMask = bitmaskFor(bitsPerCode);
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maxCode = maxCode();
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reverseTable.clear();
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LZWEncoder(final long length) {
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remaining = length;
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}
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@Override
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public void encode(final OutputStream stream, final ByteBuffer buffer) throws IOException {
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// InitializeStringTable();
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// WriteCode(ClearCode);
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// Ω = the empty string;
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// for each character in the strip {
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// K = GetNextCharacter();
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// if Ω+K is in the string table {
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// Ω = Ω+K;/* string concatenation */
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// }
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// else{
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// WriteCode (CodeFromString( Ω));
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// AddTableEntry(Ω+K);
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// Ω=K;
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// } }/*end of for loop*/
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// WriteCode (CodeFromString(Ω));
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// WriteCode (EndOfInformation);
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encodeBytes(stream, buffer);
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if (remaining < 0) {
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throw new IOException("Write past end of stream");
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}
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// TODO: Write 9 bit clear code ONLY first time!
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if (oldCode == CLEAR_CODE) {
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writeCode(stream, CLEAR_CODE);
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}
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int len = buffer.remaining();
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while (buffer.hasRemaining()) {
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byte k = buffer.get();
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LZWString string = omega.concatenate(k);
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int tableIndex = isInTable(string);
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if (tableIndex >= 0) {
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omega = string;
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oldCode = tableIndex;
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}
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else {
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writeCode(stream, oldCode);
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addStringToTable(string);
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oldCode = k & 0xff;
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omega = table[k & 0xff];
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// Handle table (almost) full
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if (tableLength >= TABLE_SIZE - 2) {
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writeCode(stream, CLEAR_CODE);
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init();
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}
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}
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}
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remaining -= len;
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// Write EOI when er are done (the API isn't very supportive of this)
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if (remaining <= 0) {
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writeCode(stream, oldCode);
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// Write EOI when er are done (the API isn't very supportive of this at the moment)
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writeCode(stream, parent);
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writeCode(stream, EOI_CODE);
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// Flush partial codes by writing 0 pad
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if (bitPos > 0) {
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writeCode(stream, 0);
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}
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}
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}
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private int isInTable(final LZWString string) {
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if (string.length == 1) {
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return string.value & 0xff;
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void encodeBytes(final OutputStream stream, final ByteBuffer buffer) throws IOException {
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int length = buffer.remaining();
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if (length == 0) {
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return;
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}
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Integer index = reverseTable.get(string);
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return index != null ? index : -1;
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if (parent == -1) {
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// Init stream
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writeCode(stream, CLEAR_CODE);
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parent = buffer.get() & 0xff;
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}
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private int addStringToTable(final LZWString string) {
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final int index = tableLength++;
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table[index] = string;
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reverseTable.put(string, index);
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while (buffer.hasRemaining()) {
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int value = buffer.get() & 0xff;
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int child = CHILDREN[parent];
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if (tableLength > maxCode) {
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if (child > 0) {
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if (SUFFIXES[child] == value) {
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parent = child;
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}
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else {
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int sibling = child;
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while (true) {
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if (SIBLINGS[sibling] > 0) {
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sibling = SIBLINGS[sibling];
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if (SUFFIXES[sibling] == value) {
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parent = sibling;
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break;
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}
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}
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else {
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SIBLINGS[sibling] = (short) nextValidCode;
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SUFFIXES[nextValidCode] = (short) value;
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writeCode(stream, parent);
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parent = value;
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nextValidCode++;
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increaseCodeSizeOrResetIfNeeded(stream);
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break;
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}
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}
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}
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}
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else {
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CHILDREN[parent] = (short) nextValidCode;
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SUFFIXES[nextValidCode] = (short) value;
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writeCode(stream, parent);
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parent = value;
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nextValidCode++;
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increaseCodeSizeOrResetIfNeeded(stream);
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}
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}
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remaining -= length;
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}
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private void increaseCodeSizeOrResetIfNeeded(final OutputStream stream) throws IOException {
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if (nextValidCode > maxCode) {
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if (bitsPerCode == MAX_BITS) {
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// Reset stream by writing Clear code
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writeCode(stream, CLEAR_CODE);
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// Reset tables
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resetTables();
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}
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else {
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// Increase code size
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bitsPerCode++;
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if (bitsPerCode > MAX_BITS) {
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throw new IllegalStateException(String.format("TIFF LZW with more than %d bits per code encountered (table overflow)", MAX_BITS));
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maxCode = maxValue(bitsPerCode);
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}
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}
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}
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bitMask = bitmaskFor(bitsPerCode);
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maxCode = maxCode();
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}
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private void resetTables() {
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Arrays.fill(CHILDREN, (short) 0);
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Arrays.fill(SIBLINGS, (short) 0);
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return index;
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bitsPerCode = MIN_BITS;
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maxCode = maxValue(bitsPerCode);
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nextValidCode = EOI_CODE + 1;
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}
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private void writeCode(final OutputStream stream, final int code) throws IOException {
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// System.err.printf("LZWEncoder.writeCode: 0x%04x\n", code);
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bits = (bits << bitsPerCode) | (code & bitMask);
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bits = (bits << bitsPerCode) | (code & maxCode);
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bitPos += bitsPerCode;
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while (bitPos >= 8) {
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@ -202,11 +201,11 @@ final class LZWEncoder implements Encoder {
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bits &= bitmaskFor(bitPos);
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}
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private static int bitmaskFor(final int bits) {
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return (1 << bits) - 1;
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private static int maxValue(final int codeLen) {
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return (1 << codeLen) - 1;
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}
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protected int maxCode() {
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return bitMask;
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private static int bitmaskFor(final int bits) {
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return maxValue(bits);
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}
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}
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