com.google.zxing.common.BitArray Maven / Gradle / Ivy
/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.common;
import java.util.Arrays;
/**
* A simple, fast array of bits, represented compactly by an array of ints internally.
*
* @author Sean Owen
*/
public final class BitArray implements Cloneable {
private int[] bits;
private int size;
public BitArray() {
this.size = 0;
this.bits = new int[1];
}
public BitArray(int size) {
this.size = size;
this.bits = makeArray(size);
}
// For testing only
BitArray(int[] bits, int size) {
this.bits = bits;
this.size = size;
}
public int getSize() {
return size;
}
public int getSizeInBytes() {
return (size + 7) / 8;
}
private void ensureCapacity(int size) {
if (size > bits.length * 32) {
int[] newBits = makeArray(size);
System.arraycopy(bits, 0, newBits, 0, bits.length);
this.bits = newBits;
}
}
/**
* @param i bit to get
* @return true iff bit i is set
*/
public boolean get(int i) {
return (bits[i / 32] & (1 << (i & 0x1F))) != 0;
}
/**
* Sets bit i.
*
* @param i bit to set
*/
public void set(int i) {
bits[i / 32] |= 1 << (i & 0x1F);
}
/**
* Flips bit i.
*
* @param i bit to set
*/
public void flip(int i) {
bits[i / 32] ^= 1 << (i & 0x1F);
}
/**
* @param from first bit to check
* @return index of first bit that is set, starting from the given index, or size if none are set
* at or beyond this given index
* @see #getNextUnset(int)
*/
public int getNextSet(int from) {
if (from >= size) {
return size;
}
int bitsOffset = from / 32;
int currentBits = bits[bitsOffset];
// mask off lesser bits first
currentBits &= ~((1 << (from & 0x1F)) - 1);
while (currentBits == 0) {
if (++bitsOffset == bits.length) {
return size;
}
currentBits = bits[bitsOffset];
}
int result = (bitsOffset * 32) + Integer.numberOfTrailingZeros(currentBits);
return result > size ? size : result;
}
/**
* @param from index to start looking for unset bit
* @return index of next unset bit, or {@code size} if none are unset until the end
* @see #getNextSet(int)
*/
public int getNextUnset(int from) {
if (from >= size) {
return size;
}
int bitsOffset = from / 32;
int currentBits = ~bits[bitsOffset];
// mask off lesser bits first
currentBits &= ~((1 << (from & 0x1F)) - 1);
while (currentBits == 0) {
if (++bitsOffset == bits.length) {
return size;
}
currentBits = ~bits[bitsOffset];
}
int result = (bitsOffset * 32) + Integer.numberOfTrailingZeros(currentBits);
return result > size ? size : result;
}
/**
* Sets a block of 32 bits, starting at bit i.
*
* @param i first bit to set
* @param newBits the new value of the next 32 bits. Note again that the least-significant bit
* corresponds to bit i, the next-least-significant to i+1, and so on.
*/
public void setBulk(int i, int newBits) {
bits[i / 32] = newBits;
}
/**
* Sets a range of bits.
*
* @param start start of range, inclusive.
* @param end end of range, exclusive
*/
public void setRange(int start, int end) {
if (end < start || start < 0 || end > size) {
throw new IllegalArgumentException();
}
if (end == start) {
return;
}
end--; // will be easier to treat this as the last actually set bit -- inclusive
int firstInt = start / 32;
int lastInt = end / 32;
for (int i = firstInt; i <= lastInt; i++) {
int firstBit = i > firstInt ? 0 : start & 0x1F;
int lastBit = i < lastInt ? 31 : end & 0x1F;
// Ones from firstBit to lastBit, inclusive
int mask = (2 << lastBit) - (1 << firstBit);
bits[i] |= mask;
}
}
/**
* Clears all bits (sets to false).
*/
public void clear() {
int max = bits.length;
for (int i = 0; i < max; i++) {
bits[i] = 0;
}
}
/**
* Efficient method to check if a range of bits is set, or not set.
*
* @param start start of range, inclusive.
* @param end end of range, exclusive
* @param value if true, checks that bits in range are set, otherwise checks that they are not set
* @return true iff all bits are set or not set in range, according to value argument
* @throws IllegalArgumentException if end is less than start or the range is not contained in the array
*/
public boolean isRange(int start, int end, boolean value) {
if (end < start || start < 0 || end > size) {
throw new IllegalArgumentException();
}
if (end == start) {
return true; // empty range matches
}
end--; // will be easier to treat this as the last actually set bit -- inclusive
int firstInt = start / 32;
int lastInt = end / 32;
for (int i = firstInt; i <= lastInt; i++) {
int firstBit = i > firstInt ? 0 : start & 0x1F;
int lastBit = i < lastInt ? 31 : end & 0x1F;
// Ones from firstBit to lastBit, inclusive
int mask = (2 << lastBit) - (1 << firstBit);
// Return false if we're looking for 1s and the masked bits[i] isn't all 1s (that is,
// equals the mask, or we're looking for 0s and the masked portion is not all 0s
if ((bits[i] & mask) != (value ? mask : 0)) {
return false;
}
}
return true;
}
public void appendBit(boolean bit) {
ensureCapacity(size + 1);
if (bit) {
bits[size / 32] |= 1 << (size & 0x1F);
}
size++;
}
/**
* Appends the least-significant bits, from value, in order from most-significant to
* least-significant. For example, appending 6 bits from 0x000001E will append the bits
* 0, 1, 1, 1, 1, 0 in that order.
*
* @param value {@code int} containing bits to append
* @param numBits bits from value to append
*/
public void appendBits(int value, int numBits) {
if (numBits < 0 || numBits > 32) {
throw new IllegalArgumentException("Num bits must be between 0 and 32");
}
ensureCapacity(size + numBits);
for (int numBitsLeft = numBits; numBitsLeft > 0; numBitsLeft--) {
appendBit(((value >> (numBitsLeft - 1)) & 0x01) == 1);
}
}
public void appendBitArray(BitArray other) {
int otherSize = other.size;
ensureCapacity(size + otherSize);
for (int i = 0; i < otherSize; i++) {
appendBit(other.get(i));
}
}
public void xor(BitArray other) {
if (size != other.size) {
throw new IllegalArgumentException("Sizes don't match");
}
for (int i = 0; i < bits.length; i++) {
// The last int could be incomplete (i.e. not have 32 bits in
// it) but there is no problem since 0 XOR 0 == 0.
bits[i] ^= other.bits[i];
}
}
/**
*
* @param bitOffset first bit to start writing
* @param array array to write into. Bytes are written most-significant byte first. This is the opposite
* of the internal representation, which is exposed by {@link #getBitArray()}
* @param offset position in array to start writing
* @param numBytes how many bytes to write
*/
public void toBytes(int bitOffset, byte[] array, int offset, int numBytes) {
for (int i = 0; i < numBytes; i++) {
int theByte = 0;
for (int j = 0; j < 8; j++) {
if (get(bitOffset)) {
theByte |= 1 << (7 - j);
}
bitOffset++;
}
array[offset + i] = (byte) theByte;
}
}
/**
* @return underlying array of ints. The first element holds the first 32 bits, and the least
* significant bit is bit 0.
*/
public int[] getBitArray() {
return bits;
}
/**
* Reverses all bits in the array.
*/
public void reverse() {
int[] newBits = new int[bits.length];
// reverse all int's first
int len = (size - 1) / 32;
int oldBitsLen = len + 1;
for (int i = 0; i < oldBitsLen; i++) {
long x = bits[i];
x = ((x >> 1) & 0x55555555L) | ((x & 0x55555555L) << 1);
x = ((x >> 2) & 0x33333333L) | ((x & 0x33333333L) << 2);
x = ((x >> 4) & 0x0f0f0f0fL) | ((x & 0x0f0f0f0fL) << 4);
x = ((x >> 8) & 0x00ff00ffL) | ((x & 0x00ff00ffL) << 8);
x = ((x >> 16) & 0x0000ffffL) | ((x & 0x0000ffffL) << 16);
newBits[len - i] = (int) x;
}
// now correct the int's if the bit size isn't a multiple of 32
if (size != oldBitsLen * 32) {
int leftOffset = oldBitsLen * 32 - size;
int currentInt = newBits[0] >>> leftOffset;
for (int i = 1; i < oldBitsLen; i++) {
int nextInt = newBits[i];
currentInt |= nextInt << (32 - leftOffset);
newBits[i - 1] = currentInt;
currentInt = nextInt >>> leftOffset;
}
newBits[oldBitsLen - 1] = currentInt;
}
bits = newBits;
}
private static int[] makeArray(int size) {
return new int[(size + 31) / 32];
}
@Override
public boolean equals(Object o) {
if (!(o instanceof BitArray)) {
return false;
}
BitArray other = (BitArray) o;
return size == other.size && Arrays.equals(bits, other.bits);
}
@Override
public int hashCode() {
return 31 * size + Arrays.hashCode(bits);
}
@Override
public String toString() {
StringBuilder result = new StringBuilder(size);
for (int i = 0; i < size; i++) {
if ((i & 0x07) == 0) {
result.append(' ');
}
result.append(get(i) ? 'X' : '.');
}
return result.toString();
}
@Override
public BitArray clone() {
return new BitArray(bits.clone(), size);
}
}