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/**
* 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.hadoop.util;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import java.io.IOException;
import java.util.Arrays;
/**
* This class provides utilities for working with CRCs.
*/
@InterfaceAudience.LimitedPrivate({"Common", "HDFS", "MapReduce", "Yarn"})
@InterfaceStability.Unstable
public final class CrcUtil {
public static final int MULTIPLICATIVE_IDENTITY = 0x80000000;
public static final int GZIP_POLYNOMIAL = 0xEDB88320;
public static final int CASTAGNOLI_POLYNOMIAL = 0x82F63B78;
/**
* Hide default constructor for a static utils class.
*/
private CrcUtil() {
}
/**
* Compute x^({@code lengthBytes} * 8) mod {@code mod}, where {@code mod} is
* in "reversed" (little-endian) format such that {@code mod & 1} represents
* x^31 and has an implicit term x^32.
*/
public static int getMonomial(long lengthBytes, int mod) {
if (lengthBytes == 0) {
return MULTIPLICATIVE_IDENTITY;
} else if (lengthBytes < 0) {
throw new IllegalArgumentException(
"lengthBytes must be positive, got " + lengthBytes);
}
// Decompose into
// x^degree == x ^ SUM(bit[i] * 2^i) == PRODUCT(x ^ (bit[i] * 2^i))
// Generate each x^(2^i) by squaring.
// Since 'degree' is in 'bits', but we only need to support byte
// granularity we can begin with x^8.
int multiplier = MULTIPLICATIVE_IDENTITY >>> 8;
int product = MULTIPLICATIVE_IDENTITY;
long degree = lengthBytes;
while (degree > 0) {
if ((degree & 1) != 0) {
product = (product == MULTIPLICATIVE_IDENTITY) ? multiplier :
galoisFieldMultiply(product, multiplier, mod);
}
multiplier = galoisFieldMultiply(multiplier, multiplier, mod);
degree >>= 1;
}
return product;
}
/**
* @param monomial Precomputed x^(lengthBInBytes * 8) mod {@code mod}
*/
public static int composeWithMonomial(
int crcA, int crcB, int monomial, int mod) {
return galoisFieldMultiply(crcA, monomial, mod) ^ crcB;
}
/**
* @param lengthB length of content corresponding to {@code crcB}, in bytes.
*/
public static int compose(int crcA, int crcB, long lengthB, int mod) {
int monomial = getMonomial(lengthB, mod);
return composeWithMonomial(crcA, crcB, monomial, mod);
}
/**
* @return 4-byte array holding the big-endian representation of
* {@code value}.
*/
public static byte[] intToBytes(int value) {
byte[] buf = new byte[4];
try {
writeInt(buf, 0, value);
} catch (IOException ioe) {
// Since this should only be able to occur from code bugs within this
// class rather than user input, we throw as a RuntimeException
// rather than requiring this method to declare throwing IOException
// for something the caller can't control.
throw new RuntimeException(ioe);
}
return buf;
}
/**
* Writes big-endian representation of {@code value} into {@code buf}
* starting at {@code offset}. buf.length must be greater than or
* equal to offset + 4.
*/
public static void writeInt(byte[] buf, int offset, int value)
throws IOException {
if (offset + 4 > buf.length) {
throw new IOException(String.format(
"writeInt out of bounds: buf.length=%d, offset=%d",
buf.length, offset));
}
buf[offset + 0] = (byte)((value >>> 24) & 0xff);
buf[offset + 1] = (byte)((value >>> 16) & 0xff);
buf[offset + 2] = (byte)((value >>> 8) & 0xff);
buf[offset + 3] = (byte)(value & 0xff);
}
/**
* Reads 4-byte big-endian int value from {@code buf} starting at
* {@code offset}. buf.length must be greater than or equal to offset + 4.
*/
public static int readInt(byte[] buf, int offset)
throws IOException {
if (offset + 4 > buf.length) {
throw new IOException(String.format(
"readInt out of bounds: buf.length=%d, offset=%d",
buf.length, offset));
}
int value = ((buf[offset + 0] & 0xff) << 24) |
((buf[offset + 1] & 0xff) << 16) |
((buf[offset + 2] & 0xff) << 8) |
((buf[offset + 3] & 0xff));
return value;
}
/**
* For use with debug statements; verifies bytes.length on creation,
* expecting it to represent exactly one CRC, and returns a hex
* formatted value.
*/
public static String toSingleCrcString(final byte[] bytes)
throws IOException {
if (bytes.length != 4) {
throw new IOException((String.format(
"Unexpected byte[] length '%d' for single CRC. Contents: %s",
bytes.length, Arrays.toString(bytes))));
}
return String.format("0x%08x", readInt(bytes, 0));
}
/**
* For use with debug statements; verifies bytes.length on creation,
* expecting it to be divisible by CRC byte size, and returns a list of
* hex formatted values.
*/
public static String toMultiCrcString(final byte[] bytes)
throws IOException {
if (bytes.length % 4 != 0) {
throw new IOException((String.format(
"Unexpected byte[] length '%d' not divisible by 4. Contents: %s",
bytes.length, Arrays.toString(bytes))));
}
StringBuilder sb = new StringBuilder();
sb.append('[');
for (int i = 0; i < bytes.length; i += 4) {
sb.append(String.format("0x%08x", readInt(bytes, i)));
if (i != bytes.length - 4) {
sb.append(", ");
}
}
sb.append(']');
return sb.toString();
}
/**
* Galois field multiplication of {@code p} and {@code q} with the
* generator polynomial {@code m} as the modulus.
*
* @param m The little-endian polynomial to use as the modulus when
* multiplying p and q, with implicit "1" bit beyond the bottom bit.
*/
private static int galoisFieldMultiply(int p, int q, int m) {
int summation = 0;
// Top bit is the x^0 place; each right-shift increments the degree of the
// current term.
int curTerm = MULTIPLICATIVE_IDENTITY;
// Iteratively multiply p by x mod m as we go to represent the q[i] term
// (of degree x^i) times p.
int px = p;
while (curTerm != 0) {
if ((q & curTerm) != 0) {
summation ^= px;
}
// Bottom bit represents highest degree since we're little-endian; before
// we multiply by "x" for the next term, check bottom bit to know whether
// the resulting px will thus have a term matching the implicit "1" term
// of "m" and thus will need to subtract "m" after mutiplying by "x".
boolean hasMaxDegree = ((px & 1) != 0);
px >>>= 1;
if (hasMaxDegree) {
px ^= m;
}
curTerm >>>= 1;
}
return summation;
}
}
