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ImageIO plugin for Google WebP File Format (WebP).
/*
* Copyright (c) 2020, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
package com.twelvemonkeys.imageio.plugins.webp;
import javax.imageio.stream.ImageInputStream;
import java.io.EOFException;
import java.io.IOException;
import static com.twelvemonkeys.lang.Validate.notNull;
/**
* LSBBitReader
*
* @author Harald Kuhr
* @author Simon Kammermeier
*/
public final class LSBBitReader {
// TODO: Consider creating an ImageInputStream wrapper with the WebP implementation of readBit(s)?
private final ImageInputStream imageInput;
int bitOffset = 64;
long streamPosition = -1;
/**
* Pre-buffers up to the next 8 Bytes in input.
* Contains valid bits in bits 63 to {@code bitOffset} (inclusive).
*/
private long buffer;
public LSBBitReader(ImageInputStream imageInput) {
this.imageInput = notNull(imageInput);
}
/**
* Reads the specified number of bits from the stream in an LSB-first way and advances the bitOffset.
* The underlying ImageInputStream will be advanced to the first not (completely) read byte.
* Requesting more than 64 bits will advance the reader by the correct amount and return the lowest 64 bits of
* the read number
*
* @param bits the number of bits to read
* @return a signed long built from the requested bits (truncated to the low 64 bits)
* @throws IOException if an I/O error occurs
* @see LSBBitReader#peekBits
*/
public long readBits(int bits) throws IOException {
return readBits(bits, false);
}
/**
* Reads the specified number of bits from the buffer in an LSB-first way.
* Does not advance the bitOffset or the underlying input stream.
* As only 56 bits are buffered (in the worst case) peeking more is not possible without advancing the reader and
* as such disallowed.
*
* @param bits the number of bits to peek (max 56)
* @return a signed long built from the requested bits
* @throws IOException if an I/O error occurs
* @see LSBBitReader#readBits
*/
public long peekBits(int bits) throws IOException {
if (bits > 56) {
throw new IllegalArgumentException("Tried peeking over 56");
}
return readBits(bits, true);
}
private long readBits(int bits, boolean peek) throws IOException {
if (bits <= 56) {
// Could eliminate if we never read from the underlying InputStream
// outside this class after the object is created
if (streamPosition != imageInput.getStreamPosition()) {
// Need to reset buffer as stream was read in the meantime
resetBuffer();
}
long ret = (buffer >>> bitOffset) & ((1L << bits) - 1);
if (!peek) {
bitOffset += bits;
if (bitOffset >= 8) {
refillBuffer();
}
}
return ret;
}
else {
// Peek always false in this case
long lower = readBits(56);
return (readBits(bits - 56) << (56)) | lower;
}
}
private void refillBuffer() throws IOException {
// Set to stream position consistent with buffered bytes
imageInput.seek(streamPosition + 8);
for (; bitOffset >= 8; bitOffset -= 8) {
try {
byte b = imageInput.readByte();
buffer >>>= 8;
streamPosition++;
buffer |= ((long) b << 56);
}
catch (EOFException e) {
imageInput.seek(streamPosition);
return;
}
}
// Reset to guarantee stream position consistent with returned bytes
// Would not need to do this seeking around when the underlying ImageInputStream is never read from outside
// this class after the object is created.
imageInput.seek(streamPosition);
}
private void resetBuffer() throws IOException {
long inputStreamPosition = imageInput.getStreamPosition();
try {
buffer = imageInput.readLong();
bitOffset = 0;
streamPosition = inputStreamPosition;
imageInput.seek(inputStreamPosition);
}
catch (EOFException e) {
// Retry byte by byte
streamPosition = inputStreamPosition - 8;
bitOffset = 64;
refillBuffer();
}
}
// Left for backwards compatibility / Compatibility with ImageInputStream interface
public int readBit() throws IOException {
return (int) readBits(1);
}
}