/*
* #%L
* BSD implementations of Bio-Formats readers and writers
* %%
* Copyright (C) 2005 - 2015 Open Microscopy Environment:
* - Board of Regents of the University of Wisconsin-Madison
* - Glencoe Software, Inc.
* - University of Dundee
* %%
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. 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.
*
* 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 HOLDERS 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.
* #L%
*/
package loci.formats.codec;
import java.util.Random;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A class for reading arbitrary numbers of bits from a byte array.
*
* @author Eric Kjellman egkjellman at wisc.edu
* @deprecated Use loci.common.RandomAccessInputStream instead
*/
public class BitBuffer {
// -- Constants --
private static final Logger LOGGER = LoggerFactory.getLogger(BitBuffer.class);
/** Various bitmasks for the 0000xxxx side of a byte. */
private static final int[] BACK_MASK = {
0x00, // 00000000
0x01, // 00000001
0x03, // 00000011
0x07, // 00000111
0x0F, // 00001111
0x1F, // 00011111
0x3F, // 00111111
0x7F // 01111111
};
/** Various bitmasks for the xxxx0000 side of a byte. */
private static final int[] FRONT_MASK = {
0x0000, // 00000000
0x0080, // 10000000
0x00C0, // 11000000
0x00E0, // 11100000
0x00F0, // 11110000
0x00F8, // 11111000
0x00FC, // 11111100
0x00FE // 11111110
};
private byte[] byteBuffer;
private int currentByte;
private int currentBit;
private int eofByte;
private boolean eofFlag;
/** Default constructor. */
public BitBuffer(byte[] byteBuffer) {
this.byteBuffer = byteBuffer;
currentByte = 0;
currentBit = 0;
eofByte = byteBuffer.length;
}
/** Return the backing byte array. */
public byte[] getByteBuffer() {
return byteBuffer;
}
/**
* Skips a number of bits in the BitBuffer.
*
* @param bits Number of bits to skip
*/
public void skipBits(long bits) {
if (bits < 0) {
throw new IllegalArgumentException("Bits to skip may not be negative");
}
// handles skipping past eof
if ((long) eofByte * 8 < (long) currentByte * 8 + currentBit + bits) {
eofFlag = true;
currentByte = eofByte;
currentBit = 0;
return;
}
int skipBytes = (int) (bits / 8);
int skipBits = (int) (bits % 8);
currentByte += skipBytes;
currentBit += skipBits;
while (currentBit >= 8) {
currentByte++;
currentBit -= 8;
}
}
/**
* Returns an int value representing the value of the bits read from
* the byte array, from the current position. Bits are extracted from the
* "left side" or high side of the byte.<p>
* The current position is modified by this call.<p>
* Bits are pushed into the int from the right, endianness is not
* considered by the method on its own. So, if 5 bits were read from the
* buffer "10101", the int would be the integer representation of
* 000...0010101 on the target machine. <p>
* In general, this also means the result will be positive unless a full
* 32 bits are read. <p>
* Requesting more than 32 bits is allowed, but only up to 32 bits worth of
* data will be returned (the last 32 bits read). <p>
*
* @param bitsToRead the number of bits to read from the bit buffer
* @return the value of the bits read
*/
public int getBits(int bitsToRead) {
if (bitsToRead < 0) {
throw new IllegalArgumentException("Bits to read may not be negative");
}
if (bitsToRead == 0) return 0;
if (eofFlag) return -1; // Already at end of file
int toStore = 0;
while (bitsToRead != 0 && !eofFlag) {
if (currentBit < 0 || currentBit > 7) {
throw new IllegalStateException("byte=" +
currentByte + ", bit = " + currentBit);
}
// if we need to read from more than the current byte in the buffer...
int bitsLeft = 8 - currentBit;
if (bitsToRead >= bitsLeft) {
toStore <<= bitsLeft;
bitsToRead -= bitsLeft;
int cb = (int) byteBuffer[currentByte];
if (currentBit == 0) {
// we can read in a whole byte, so we'll do that.
toStore += cb & 0xff;
}
else {
// otherwise, only read the appropriate number of bits off the back
// side of the byte, in order to "finish" the current byte in the
// buffer.
toStore += cb & BACK_MASK[bitsLeft];
currentBit = 0;
}
currentByte++;
}
else {
// We will be able to finish using the current byte.
// read the appropriate number of bits off the front side of the byte,
// then push them into the int.
toStore = toStore << bitsToRead;
int cb = byteBuffer[currentByte] & 0xff;
toStore += (cb & (0x00FF - FRONT_MASK[currentBit])) >>
(bitsLeft - bitsToRead);
currentBit += bitsToRead;
bitsToRead = 0;
}
// If we reach the end of the buffer, return what we currently have.
if (currentByte == eofByte) {
eofFlag = true;
return toStore;
}
}
return toStore;
}
/**
* Checks if the current position is on a byte boundary, that is the next
* bit in the byte array is the first bit in a byte.
*
* @return true if bit is on byte boundary, false otherwise.
*/
public boolean isBitOnByteBoundary() {
return currentBit % 8 == 0 ? true : false;
}
/**
* Testing method.
* @param args Ignored.
*/
public static void main(String[] args) {
int trials = 50000;
int[] nums = new int[trials];
int[] len = new int[trials];
BitWriter bw = new BitWriter();
int totallen = 0;
Random r = new Random();
LOGGER.info("Generating {} trials.", trials);
LOGGER.info("Writing to byte array");
// we want the trials to be able to be all possible bit lengths.
// r.nextInt() by itself is not sufficient... in 50000 trials it would be
// extremely unlikely to produce bit strings of 1 bit.
// instead, we randomly choose from 0 to 2^(i % 32).
// Except, 1 << 31 is a negative number in two's complement, so we make it
// a random number in the entire range.
for (int i = 0; i < trials; i++) {
if (31 == i % 32) {
nums[i] = r.nextInt();
}
else {
nums[i] = r.nextInt(1 << (i % 32));
}
// How many bits are required to represent this number?
len[i] = (Integer.toBinaryString(nums[i])).length();
totallen += len[i];
bw.write(nums[i], len[i]);
}
BitBuffer bb = new BitBuffer(bw.toByteArray());
int readint;
LOGGER.info("Reading from BitBuffer");
// Randomly skip or read bytes
for (int i = 0; i < trials; i++) {
int c = r.nextInt(100);
if (c > 50) {
readint = bb.getBits(len[i]);
if (readint != nums[i]) {
LOGGER.info("Error at #{}: {} received, {} expected.",
new Object[] {i, readint, nums[i]});
}
}
else {
bb.skipBits(len[i]);
}
}
// Test reading past end of buffer.
LOGGER.info("Testing end of buffer");
bb = new BitBuffer(bw.toByteArray());
// The total length could be mid byte. Add one byte to test.
bb.skipBits(totallen + 8);
int read = bb.getBits(1);
if (-1 != read) {
LOGGER.info("-1 expected at end of buffer, {} received.", read);
}
// Test byte boundary detection
LOGGER.info("Testing byte boundary detection");
bb = new BitBuffer(bw.toByteArray());
for (int i = 0; i < trials; i++) {
int c = r.nextInt(100);
if (c > 50) {
if (len[i] > 8) {
bb.getBits(8);
if (!bb.isBitOnByteBoundary()){
LOGGER.info("Bit on byte boundary expected, but not returned.");
}
}
}
}
}
}