BitString.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to you 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 org.apache.calcite.util;
import org.checkerframework.checker.nullness.qual.Nullable;
import java.math.BigInteger;
import java.util.List;
import static java.util.Objects.requireNonNull;
/**
* String of bits.
*
* <p>A bit string logically consists of a set of '0' and '1' values, of a
* specified length. The length is preserved even if this means that the bit
* string has leading '0's.
*
* <p>You can create a bit string from a string of 0s and 1s
* ({@link #BitString(String, int)} or {@link #createFromBitString}), or from a
* string of hex digits ({@link #createFromHexString}). You can convert it to a
* byte array ({@link #getAsByteArray}), to a bit string ({@link #toBitString}),
* or to a hex string ({@link #toHexString}). A utility method
* {@link #toByteArrayFromBitString} converts a bit string directly to a byte
* array.
*
* <p>This class is immutable: once created, none of the methods modify the
* value.
*/
public class BitString {
//~ Instance fields --------------------------------------------------------
private final String bits;
private final int bitCount;
//~ Constructors -----------------------------------------------------------
protected BitString(
String bits,
int bitCount) {
assert bits.replace("1", "").replace("0", "").length() == 0
: "bit string '" + bits + "' contains digits other than {0, 1}";
this.bits = bits;
this.bitCount = bitCount;
}
//~ Methods ----------------------------------------------------------------
/**
* Creates a BitString representation out of a Hex String. Initial zeros are
* be preserved. Hex String is defined in the SQL standard to be a string
* with odd number of hex digits. An even number of hex digits is in the
* standard a Binary String.
*
* @param s a string, in hex notation
* @throws NumberFormatException if <code>s</code> is invalid.
*/
public static BitString createFromHexString(String s) {
int bitCount = s.length() * 4;
String bits = (bitCount == 0) ? "" : new BigInteger(s, 16).toString(2);
return new BitString(bits, bitCount);
}
/**
* Creates a BitString representation out of a Bit String. Initial zeros are
* be preserved.
*
* @param s a string of 0s and 1s.
* @throws NumberFormatException if <code>s</code> is invalid.
*/
public static BitString createFromBitString(String s) {
int n = s.length();
if (n > 0) { // check that S is valid
Util.discard(new BigInteger(s, 2));
}
return new BitString(s, n);
}
@Override public String toString() {
return toBitString();
}
@Override public int hashCode() {
return bits.hashCode() + bitCount;
}
@Override public boolean equals(@Nullable Object o) {
return o == this
|| o instanceof BitString
&& bits.equals(((BitString) o).bits)
&& bitCount == ((BitString) o).bitCount;
}
public int getBitCount() {
return bitCount;
}
public byte[] getAsByteArray() {
return toByteArrayFromBitString(bits, bitCount);
}
/**
* Returns this bit string as a bit string, such as "10110".
*/
public String toBitString() {
return bits;
}
/**
* Converts this bit string to a hex string, such as "7AB".
*/
public String toHexString() {
byte[] bytes = getAsByteArray();
String s = ConversionUtil.toStringFromByteArray(bytes, 16);
switch (bitCount % 8) {
case 1: // B'1' -> X'1'
case 2: // B'10' -> X'2'
case 3: // B'100' -> X'4'
case 4: // B'1000' -> X'8'
return s.substring(1);
case 5: // B'10000' -> X'10'
case 6: // B'100000' -> X'20'
case 7: // B'1000000' -> X'40'
case 0: // B'10000000' -> X'80', and B'' -> X''
return s;
default:
break;
}
if ((bitCount % 8) == 4) {
return s.substring(1);
} else {
return s;
}
}
/**
* Converts a bit string to an array of bytes.
*/
public static byte[] toByteArrayFromBitString(
String bits,
int bitCount) {
if (bitCount < 0) {
return new byte[0];
}
int byteCount = (bitCount + 7) / 8;
byte[] srcBytes;
if (bits.length() > 0) {
BigInteger bigInt = new BigInteger(bits, 2);
srcBytes = bigInt.toByteArray();
} else {
srcBytes = new byte[0];
}
byte[] dest = new byte[byteCount];
// If the number started with 0s, the array won't be very long. Assume
// that ret is already initialized to 0s, and just copy into the
// RHS of it.
int bytesToCopy = Math.min(byteCount, srcBytes.length);
System.arraycopy(
srcBytes,
srcBytes.length - bytesToCopy,
dest,
dest.length - bytesToCopy,
bytesToCopy);
return dest;
}
/**
* Concatenates some BitStrings. Concatenates all at once, not pairwise, to
* avoid string copies.
*
* @param args BitString[]
*/
public static BitString concat(List<BitString> args) {
if (args.size() < 2) {
return args.get(0);
}
int length = 0;
for (BitString arg : args) {
length += arg.bitCount;
}
StringBuilder sb = new StringBuilder(length);
for (BitString arg1 : args) {
sb.append(arg1.bits);
}
return new BitString(
sb.toString(),
length);
}
/**
* Creates a BitString from an array of bytes.
*
* @param bytes Bytes
* @return BitString
*/
public static BitString createFromBytes(byte[] bytes) {
int bitCount = requireNonNull(bytes, "bytes").length * 8;
StringBuilder sb = new StringBuilder(bitCount);
for (byte b : bytes) {
final String s = Integer.toBinaryString(Byte.toUnsignedInt(b));
for (int i = s.length(); i < 8; i++) {
sb.append('0'); // pad to length 8
}
sb.append(s);
}
return new BitString(sb.toString(), bitCount);
}
}