From 99d8dfc7f401d8f9c2469b67e56240a33a0152a9 Mon Sep 17 00:00:00 2001
From: Todd Lipcon <todd@cloudera.com>
Date: Wed, 26 Aug 2009 11:32:55 -0700
Subject: [PATCH] HADOOP-6148. Implement a fast, pure Java CRC32 calculator which outperforms java.util.zip.CRC32. Contributed by Todd Lipcon and Scott Carey

---
 .../org/apache/hadoop/fs/ChecksumFileSystem.java   |    5 +-
 src/core/org/apache/hadoop/util/DataChecksum.java  |   10 +-
 src/core/org/apache/hadoop/util/PureJavaCrc32.java |  351 ++++++++++++++++++++
 .../org/apache/hadoop/util/TestPureJavaCrc32.java  |  301 +++++++++++++++++
 4 files changed, 660 insertions(+), 7 deletions(-)
 create mode 100644 src/core/org/apache/hadoop/util/PureJavaCrc32.java
 create mode 100644 src/test/org/apache/hadoop/util/TestPureJavaCrc32.java

diff --git a/src/core/org/apache/hadoop/fs/ChecksumFileSystem.java b/src/core/org/apache/hadoop/fs/ChecksumFileSystem.java
index 72a09bd..6f9701e 100644
--- a/src/core/org/apache/hadoop/fs/ChecksumFileSystem.java
+++ b/src/core/org/apache/hadoop/fs/ChecksumFileSystem.java
@@ -27,6 +27,7 @@ import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.util.Progressable;
+import org.apache.hadoop.util.PureJavaCrc32;
 import org.apache.hadoop.util.StringUtils;
 
 /****************************************************************
@@ -135,7 +136,7 @@ public abstract class ChecksumFileSystem extends FilterFileSystem {
         if (!Arrays.equals(version, CHECKSUM_VERSION))
           throw new IOException("Not a checksum file: "+sumFile);
         this.bytesPerSum = sums.readInt();
-        set(fs.verifyChecksum, new CRC32(), bytesPerSum, 4);
+        set(fs.verifyChecksum, new PureJavaCrc32(), bytesPerSum, 4);
       } catch (FileNotFoundException e) {         // quietly ignore
         set(fs.verifyChecksum, null, 1, 0);
       } catch (IOException e) {                   // loudly ignore
@@ -330,7 +331,7 @@ public abstract class ChecksumFileSystem extends FilterFileSystem {
                           long blockSize,
                           Progressable progress)
       throws IOException {
-      super(new CRC32(), fs.getBytesPerSum(), 4);
+      super(new PureJavaCrc32(), fs.getBytesPerSum(), 4);
       int bytesPerSum = fs.getBytesPerSum();
       this.datas = fs.getRawFileSystem().create(file, overwrite, bufferSize, 
                                          replication, blockSize, progress);
diff --git a/src/core/org/apache/hadoop/util/DataChecksum.java b/src/core/org/apache/hadoop/util/DataChecksum.java
index 9aa3390..eb529bc 100644
--- a/src/core/org/apache/hadoop/util/DataChecksum.java
+++ b/src/core/org/apache/hadoop/util/DataChecksum.java
@@ -16,7 +16,7 @@
  * limitations under the License.
  */
 
-package org.apache.hadoop.util;
+package org.apache.hadoop.util;
 
 import java.util.zip.Checksum;
 import java.util.zip.CRC32;
@@ -51,7 +51,7 @@ public class DataChecksum implements Checksum {
       return new DataChecksum( CHECKSUM_NULL, new ChecksumNull(), 
                                CHECKSUM_NULL_SIZE, bytesPerChecksum );
     case CHECKSUM_CRC32 :
-      return new DataChecksum( CHECKSUM_CRC32, new CRC32(), 
+      return new DataChecksum( CHECKSUM_CRC32, new PureJavaCrc32(), 
                                CHECKSUM_CRC32_SIZE, bytesPerChecksum );
     default:
       return null;  
@@ -205,10 +205,10 @@ public class DataChecksum implements Checksum {
   public int getNumBytesInSum() {
     return inSum;
   }
-  
-  public static final int SIZE_OF_INTEGER = Integer.SIZE / Byte.SIZE;
+  
+  public static final int SIZE_OF_INTEGER = Integer.SIZE / Byte.SIZE;
   static public int getChecksumHeaderSize() {
-    return 1 + SIZE_OF_INTEGER; // type byte, bytesPerChecksum int
+    return 1 + SIZE_OF_INTEGER; // type byte, bytesPerChecksum int
   }
   //Checksum Interface. Just a wrapper around member summer.
   public long getValue() {
diff --git a/src/core/org/apache/hadoop/util/PureJavaCrc32.java b/src/core/org/apache/hadoop/util/PureJavaCrc32.java
new file mode 100644
index 0000000..206f931
--- /dev/null
+++ b/src/core/org/apache/hadoop/util/PureJavaCrc32.java
@@ -0,0 +1,351 @@
+/**
+ * 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 java.util.zip.Checksum;
+
+/**
+ * A pure-java implementation of the CRC32 checksum that uses
+ * the same polynomial as the built-in native CRC32.
+ *
+ * This is to avoid the JNI overhead for certain uses of Checksumming
+ * where many small pieces of data are checksummed in succession.
+ *
+ * The current version is ~10x to 1.8x as fast as Sun's native
+ * java.util.zip.CRC32 in Java 1.6
+ *
+ * @see java.util.zip.CRC32
+ */
+public class PureJavaCrc32 implements Checksum {
+
+  /** the current CRC value, bit-flipped */
+  private int crc;
+
+  public PureJavaCrc32() {
+    reset();
+  }
+
+  /** {@inheritDoc} */
+  public long getValue() {
+    return (~crc) & 0xffffffffL;
+  }
+
+  /** {@inheritDoc} */
+  public void reset() {
+    crc = 0xffffffff;
+  }
+
+  /** {@inheritDoc} */
+  public void update(byte[] b, int off, int len) {
+    while(len > 3) {
+      int c0 = crc ^ b[off++];
+      int c1 = (crc >>>= 8) ^ b[off++];
+      int c2 = (crc >>>= 8) ^ b[off++];
+      int c3 = (crc >>>= 8) ^ b[off++];
+      crc = T4[c0 & 0xff] ^ T3[c1 & 0xff] ^ T2[c2 & 0xff] ^ T1[c3 & 0xff];
+      len -= 4;
+    }
+    while(len > 0) {
+      crc = (crc >>> 8) ^ T1[(crc ^ b[off++]) & 0xff];
+      len--;
+    }
+  }
+
+  /** {@inheritDoc} */
+  final public void update(int b) {
+    crc = (crc >>> 8) ^ T1[(crc ^ b) & 0xff];
+  }
+
+  /**
+   * Pre-generated lookup tables. For the code to generate these tables
+   * please see HDFS-297.
+   */
+
+  /** T1[x] is ~CRC(x) */
+  private static final int[] T1 = new int[] {
+    0x0, 0x77073096, 0xee0e612c, 0x990951ba,
+    0x76dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
+    0xedb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
+    0x9b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
+    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
+    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
+    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
+    0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
+    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
+    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
+    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
+    0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
+    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
+    0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
+    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
+    0x76dc4190, 0x1db7106, 0x98d220bc, 0xefd5102a,
+    0x71b18589, 0x6b6b51f, 0x9fbfe4a5, 0xe8b8d433,
+    0x7807c9a2, 0xf00f934, 0x9609a88e, 0xe10e9818,
+    0x7f6a0dbb, 0x86d3d2d, 0x91646c97, 0xe6635c01,
+    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
+    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
+    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
+    0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
+    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
+    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
+    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
+    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
+    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
+    0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
+    0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
+    0xedb88320, 0x9abfb3b6, 0x3b6e20c, 0x74b1d29a,
+    0xead54739, 0x9dd277af, 0x4db2615, 0x73dc1683,
+    0xe3630b12, 0x94643b84, 0xd6d6a3e, 0x7a6a5aa8,
+    0xe40ecf0b, 0x9309ff9d, 0xa00ae27, 0x7d079eb1,
+    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
+    0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
+    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
+    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
+    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
+    0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
+    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
+    0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
+    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
+    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
+    0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
+    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x26d930a,
+    0x9c0906a9, 0xeb0e363f, 0x72076785, 0x5005713,
+    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0xcb61b38,
+    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0xbdbdf21,
+    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
+    0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
+    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
+    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
+    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
+    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
+    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
+    0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
+    0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
+    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
+    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
+  };
+
+  /** T2[x] is ~CRC(x followed by one 0x00 byte) */
+  private static final int[] T2 = new int[] {
+    0x0, 0x191b3141, 0x32366282, 0x2b2d53c3,
+    0x646cc504, 0x7d77f445, 0x565aa786, 0x4f4196c7,
+    0xc8d98a08, 0xd1c2bb49, 0xfaefe88a, 0xe3f4d9cb,
+    0xacb54f0c, 0xb5ae7e4d, 0x9e832d8e, 0x87981ccf,
+    0x4ac21251, 0x53d92310, 0x78f470d3, 0x61ef4192,
+    0x2eaed755, 0x37b5e614, 0x1c98b5d7, 0x5838496,
+    0x821b9859, 0x9b00a918, 0xb02dfadb, 0xa936cb9a,
+    0xe6775d5d, 0xff6c6c1c, 0xd4413fdf, 0xcd5a0e9e,
+    0x958424a2, 0x8c9f15e3, 0xa7b24620, 0xbea97761,
+    0xf1e8e1a6, 0xe8f3d0e7, 0xc3de8324, 0xdac5b265,
+    0x5d5daeaa, 0x44469feb, 0x6f6bcc28, 0x7670fd69,
+    0x39316bae, 0x202a5aef, 0xb07092c, 0x121c386d,
+    0xdf4636f3, 0xc65d07b2, 0xed705471, 0xf46b6530,
+    0xbb2af3f7, 0xa231c2b6, 0x891c9175, 0x9007a034,
+    0x179fbcfb, 0xe848dba, 0x25a9de79, 0x3cb2ef38,
+    0x73f379ff, 0x6ae848be, 0x41c51b7d, 0x58de2a3c,
+    0xf0794f05, 0xe9627e44, 0xc24f2d87, 0xdb541cc6,
+    0x94158a01, 0x8d0ebb40, 0xa623e883, 0xbf38d9c2,
+    0x38a0c50d, 0x21bbf44c, 0xa96a78f, 0x138d96ce,
+    0x5ccc0009, 0x45d73148, 0x6efa628b, 0x77e153ca,
+    0xbabb5d54, 0xa3a06c15, 0x888d3fd6, 0x91960e97,
+    0xded79850, 0xc7cca911, 0xece1fad2, 0xf5facb93,
+    0x7262d75c, 0x6b79e61d, 0x4054b5de, 0x594f849f,
+    0x160e1258, 0xf152319, 0x243870da, 0x3d23419b,
+    0x65fd6ba7, 0x7ce65ae6, 0x57cb0925, 0x4ed03864,
+    0x191aea3, 0x188a9fe2, 0x33a7cc21, 0x2abcfd60,
+    0xad24e1af, 0xb43fd0ee, 0x9f12832d, 0x8609b26c,
+    0xc94824ab, 0xd05315ea, 0xfb7e4629, 0xe2657768,
+    0x2f3f79f6, 0x362448b7, 0x1d091b74, 0x4122a35,
+    0x4b53bcf2, 0x52488db3, 0x7965de70, 0x607eef31,
+    0xe7e6f3fe, 0xfefdc2bf, 0xd5d0917c, 0xcccba03d,
+    0x838a36fa, 0x9a9107bb, 0xb1bc5478, 0xa8a76539,
+    0x3b83984b, 0x2298a90a, 0x9b5fac9, 0x10aecb88,
+    0x5fef5d4f, 0x46f46c0e, 0x6dd93fcd, 0x74c20e8c,
+    0xf35a1243, 0xea412302, 0xc16c70c1, 0xd8774180,
+    0x9736d747, 0x8e2de606, 0xa500b5c5, 0xbc1b8484,
+    0x71418a1a, 0x685abb5b, 0x4377e898, 0x5a6cd9d9,
+    0x152d4f1e, 0xc367e5f, 0x271b2d9c, 0x3e001cdd,
+    0xb9980012, 0xa0833153, 0x8bae6290, 0x92b553d1,
+    0xddf4c516, 0xc4eff457, 0xefc2a794, 0xf6d996d5,
+    0xae07bce9, 0xb71c8da8, 0x9c31de6b, 0x852aef2a,
+    0xca6b79ed, 0xd37048ac, 0xf85d1b6f, 0xe1462a2e,
+    0x66de36e1, 0x7fc507a0, 0x54e85463, 0x4df36522,
+    0x2b2f3e5, 0x1ba9c2a4, 0x30849167, 0x299fa026,
+    0xe4c5aeb8, 0xfdde9ff9, 0xd6f3cc3a, 0xcfe8fd7b,
+    0x80a96bbc, 0x99b25afd, 0xb29f093e, 0xab84387f,
+    0x2c1c24b0, 0x350715f1, 0x1e2a4632, 0x7317773,
+    0x4870e1b4, 0x516bd0f5, 0x7a468336, 0x635db277,
+    0xcbfad74e, 0xd2e1e60f, 0xf9ccb5cc, 0xe0d7848d,
+    0xaf96124a, 0xb68d230b, 0x9da070c8, 0x84bb4189,
+    0x3235d46, 0x1a386c07, 0x31153fc4, 0x280e0e85,
+    0x674f9842, 0x7e54a903, 0x5579fac0, 0x4c62cb81,
+    0x8138c51f, 0x9823f45e, 0xb30ea79d, 0xaa1596dc,
+    0xe554001b, 0xfc4f315a, 0xd7626299, 0xce7953d8,
+    0x49e14f17, 0x50fa7e56, 0x7bd72d95, 0x62cc1cd4,
+    0x2d8d8a13, 0x3496bb52, 0x1fbbe891, 0x6a0d9d0,
+    0x5e7ef3ec, 0x4765c2ad, 0x6c48916e, 0x7553a02f,
+    0x3a1236e8, 0x230907a9, 0x824546a, 0x113f652b,
+    0x96a779e4, 0x8fbc48a5, 0xa4911b66, 0xbd8a2a27,
+    0xf2cbbce0, 0xebd08da1, 0xc0fdde62, 0xd9e6ef23,
+    0x14bce1bd, 0xda7d0fc, 0x268a833f, 0x3f91b27e,
+    0x70d024b9, 0x69cb15f8, 0x42e6463b, 0x5bfd777a,
+    0xdc656bb5, 0xc57e5af4, 0xee530937, 0xf7483876,
+    0xb809aeb1, 0xa1129ff0, 0x8a3fcc33, 0x9324fd72
+  };
+
+  /** T3[x] is ~CRC(x followed by two 0x00 bytes) */
+  private static final int[] T3 = new int[] {
+    0x0, 0x1c26a37, 0x384d46e, 0x246be59,
+    0x709a8dc, 0x6cbc2eb, 0x48d7cb2, 0x54f1685,
+    0xe1351b8, 0xfd13b8f, 0xd9785d6, 0xc55efe1,
+    0x91af964, 0x8d89353, 0xa9e2d0a, 0xb5c473d,
+    0x1c26a370, 0x1de4c947, 0x1fa2771e, 0x1e601d29,
+    0x1b2f0bac, 0x1aed619b, 0x18abdfc2, 0x1969b5f5,
+    0x1235f2c8, 0x13f798ff, 0x11b126a6, 0x10734c91,
+    0x153c5a14, 0x14fe3023, 0x16b88e7a, 0x177ae44d,
+    0x384d46e0, 0x398f2cd7, 0x3bc9928e, 0x3a0bf8b9,
+    0x3f44ee3c, 0x3e86840b, 0x3cc03a52, 0x3d025065,
+    0x365e1758, 0x379c7d6f, 0x35dac336, 0x3418a901,
+    0x3157bf84, 0x3095d5b3, 0x32d36bea, 0x331101dd,
+    0x246be590, 0x25a98fa7, 0x27ef31fe, 0x262d5bc9,
+    0x23624d4c, 0x22a0277b, 0x20e69922, 0x2124f315,
+    0x2a78b428, 0x2bbade1f, 0x29fc6046, 0x283e0a71,
+    0x2d711cf4, 0x2cb376c3, 0x2ef5c89a, 0x2f37a2ad,
+    0x709a8dc0, 0x7158e7f7, 0x731e59ae, 0x72dc3399,
+    0x7793251c, 0x76514f2b, 0x7417f172, 0x75d59b45,
+    0x7e89dc78, 0x7f4bb64f, 0x7d0d0816, 0x7ccf6221,
+    0x798074a4, 0x78421e93, 0x7a04a0ca, 0x7bc6cafd,
+    0x6cbc2eb0, 0x6d7e4487, 0x6f38fade, 0x6efa90e9,
+    0x6bb5866c, 0x6a77ec5b, 0x68315202, 0x69f33835,
+    0x62af7f08, 0x636d153f, 0x612bab66, 0x60e9c151,
+    0x65a6d7d4, 0x6464bde3, 0x662203ba, 0x67e0698d,
+    0x48d7cb20, 0x4915a117, 0x4b531f4e, 0x4a917579,
+    0x4fde63fc, 0x4e1c09cb, 0x4c5ab792, 0x4d98dda5,
+    0x46c49a98, 0x4706f0af, 0x45404ef6, 0x448224c1,
+    0x41cd3244, 0x400f5873, 0x4249e62a, 0x438b8c1d,
+    0x54f16850, 0x55330267, 0x5775bc3e, 0x56b7d609,
+    0x53f8c08c, 0x523aaabb, 0x507c14e2, 0x51be7ed5,
+    0x5ae239e8, 0x5b2053df, 0x5966ed86, 0x58a487b1,
+    0x5deb9134, 0x5c29fb03, 0x5e6f455a, 0x5fad2f6d,
+    0xe1351b80, 0xe0f771b7, 0xe2b1cfee, 0xe373a5d9,
+    0xe63cb35c, 0xe7fed96b, 0xe5b86732, 0xe47a0d05,
+    0xef264a38, 0xeee4200f, 0xeca29e56, 0xed60f461,
+    0xe82fe2e4, 0xe9ed88d3, 0xebab368a, 0xea695cbd,
+    0xfd13b8f0, 0xfcd1d2c7, 0xfe976c9e, 0xff5506a9,
+    0xfa1a102c, 0xfbd87a1b, 0xf99ec442, 0xf85cae75,
+    0xf300e948, 0xf2c2837f, 0xf0843d26, 0xf1465711,
+    0xf4094194, 0xf5cb2ba3, 0xf78d95fa, 0xf64fffcd,
+    0xd9785d60, 0xd8ba3757, 0xdafc890e, 0xdb3ee339,
+    0xde71f5bc, 0xdfb39f8b, 0xddf521d2, 0xdc374be5,
+    0xd76b0cd8, 0xd6a966ef, 0xd4efd8b6, 0xd52db281,
+    0xd062a404, 0xd1a0ce33, 0xd3e6706a, 0xd2241a5d,
+    0xc55efe10, 0xc49c9427, 0xc6da2a7e, 0xc7184049,
+    0xc25756cc, 0xc3953cfb, 0xc1d382a2, 0xc011e895,
+    0xcb4dafa8, 0xca8fc59f, 0xc8c97bc6, 0xc90b11f1,
+    0xcc440774, 0xcd866d43, 0xcfc0d31a, 0xce02b92d,
+    0x91af9640, 0x906dfc77, 0x922b422e, 0x93e92819,
+    0x96a63e9c, 0x976454ab, 0x9522eaf2, 0x94e080c5,
+    0x9fbcc7f8, 0x9e7eadcf, 0x9c381396, 0x9dfa79a1,
+    0x98b56f24, 0x99770513, 0x9b31bb4a, 0x9af3d17d,
+    0x8d893530, 0x8c4b5f07, 0x8e0de15e, 0x8fcf8b69,
+    0x8a809dec, 0x8b42f7db, 0x89044982, 0x88c623b5,
+    0x839a6488, 0x82580ebf, 0x801eb0e6, 0x81dcdad1,
+    0x8493cc54, 0x8551a663, 0x8717183a, 0x86d5720d,
+    0xa9e2d0a0, 0xa820ba97, 0xaa6604ce, 0xaba46ef9,
+    0xaeeb787c, 0xaf29124b, 0xad6fac12, 0xacadc625,
+    0xa7f18118, 0xa633eb2f, 0xa4755576, 0xa5b73f41,
+    0xa0f829c4, 0xa13a43f3, 0xa37cfdaa, 0xa2be979d,
+    0xb5c473d0, 0xb40619e7, 0xb640a7be, 0xb782cd89,
+    0xb2cddb0c, 0xb30fb13b, 0xb1490f62, 0xb08b6555,
+    0xbbd72268, 0xba15485f, 0xb853f606, 0xb9919c31,
+    0xbcde8ab4, 0xbd1ce083, 0xbf5a5eda, 0xbe9834ed
+  };
+
+  /** T4[x] is ~CRC(x followed by three 0x00 bytes) */
+  private static final int[] T4 = new int[] {
+    0x0, 0xb8bc6765, 0xaa09c88b, 0x12b5afee,
+    0x8f629757, 0x37def032, 0x256b5fdc, 0x9dd738b9,
+    0xc5b428ef, 0x7d084f8a, 0x6fbde064, 0xd7018701,
+    0x4ad6bfb8, 0xf26ad8dd, 0xe0df7733, 0x58631056,
+    0x5019579f, 0xe8a530fa, 0xfa109f14, 0x42acf871,
+    0xdf7bc0c8, 0x67c7a7ad, 0x75720843, 0xcdce6f26,
+    0x95ad7f70, 0x2d111815, 0x3fa4b7fb, 0x8718d09e,
+    0x1acfe827, 0xa2738f42, 0xb0c620ac, 0x87a47c9,
+    0xa032af3e, 0x188ec85b, 0xa3b67b5, 0xb28700d0,
+    0x2f503869, 0x97ec5f0c, 0x8559f0e2, 0x3de59787,
+    0x658687d1, 0xdd3ae0b4, 0xcf8f4f5a, 0x7733283f,
+    0xeae41086, 0x525877e3, 0x40edd80d, 0xf851bf68,
+    0xf02bf8a1, 0x48979fc4, 0x5a22302a, 0xe29e574f,
+    0x7f496ff6, 0xc7f50893, 0xd540a77d, 0x6dfcc018,
+    0x359fd04e, 0x8d23b72b, 0x9f9618c5, 0x272a7fa0,
+    0xbafd4719, 0x241207c, 0x10f48f92, 0xa848e8f7,
+    0x9b14583d, 0x23a83f58, 0x311d90b6, 0x89a1f7d3,
+    0x1476cf6a, 0xaccaa80f, 0xbe7f07e1, 0x6c36084,
+    0x5ea070d2, 0xe61c17b7, 0xf4a9b859, 0x4c15df3c,
+    0xd1c2e785, 0x697e80e0, 0x7bcb2f0e, 0xc377486b,
+    0xcb0d0fa2, 0x73b168c7, 0x6104c729, 0xd9b8a04c,
+    0x446f98f5, 0xfcd3ff90, 0xee66507e, 0x56da371b,
+    0xeb9274d, 0xb6054028, 0xa4b0efc6, 0x1c0c88a3,
+    0x81dbb01a, 0x3967d77f, 0x2bd27891, 0x936e1ff4,
+    0x3b26f703, 0x839a9066, 0x912f3f88, 0x299358ed,
+    0xb4446054, 0xcf80731, 0x1e4da8df, 0xa6f1cfba,
+    0xfe92dfec, 0x462eb889, 0x549b1767, 0xec277002,
+    0x71f048bb, 0xc94c2fde, 0xdbf98030, 0x6345e755,
+    0x6b3fa09c, 0xd383c7f9, 0xc1366817, 0x798a0f72,
+    0xe45d37cb, 0x5ce150ae, 0x4e54ff40, 0xf6e89825,
+    0xae8b8873, 0x1637ef16, 0x48240f8, 0xbc3e279d,
+    0x21e91f24, 0x99557841, 0x8be0d7af, 0x335cb0ca,
+    0xed59b63b, 0x55e5d15e, 0x47507eb0, 0xffec19d5,
+    0x623b216c, 0xda874609, 0xc832e9e7, 0x708e8e82,
+    0x28ed9ed4, 0x9051f9b1, 0x82e4565f, 0x3a58313a,
+    0xa78f0983, 0x1f336ee6, 0xd86c108, 0xb53aa66d,
+    0xbd40e1a4, 0x5fc86c1, 0x1749292f, 0xaff54e4a,
+    0x322276f3, 0x8a9e1196, 0x982bbe78, 0x2097d91d,
+    0x78f4c94b, 0xc048ae2e, 0xd2fd01c0, 0x6a4166a5,
+    0xf7965e1c, 0x4f2a3979, 0x5d9f9697, 0xe523f1f2,
+    0x4d6b1905, 0xf5d77e60, 0xe762d18e, 0x5fdeb6eb,
+    0xc2098e52, 0x7ab5e937, 0x680046d9, 0xd0bc21bc,
+    0x88df31ea, 0x3063568f, 0x22d6f961, 0x9a6a9e04,
+    0x7bda6bd, 0xbf01c1d8, 0xadb46e36, 0x15080953,
+    0x1d724e9a, 0xa5ce29ff, 0xb77b8611, 0xfc7e174,
+    0x9210d9cd, 0x2aacbea8, 0x38191146, 0x80a57623,
+    0xd8c66675, 0x607a0110, 0x72cfaefe, 0xca73c99b,
+    0x57a4f122, 0xef189647, 0xfdad39a9, 0x45115ecc,
+    0x764dee06, 0xcef18963, 0xdc44268d, 0x64f841e8,
+    0xf92f7951, 0x41931e34, 0x5326b1da, 0xeb9ad6bf,
+    0xb3f9c6e9, 0xb45a18c, 0x19f00e62, 0xa14c6907,
+    0x3c9b51be, 0x842736db, 0x96929935, 0x2e2efe50,
+    0x2654b999, 0x9ee8defc, 0x8c5d7112, 0x34e11677,
+    0xa9362ece, 0x118a49ab, 0x33fe645, 0xbb838120,
+    0xe3e09176, 0x5b5cf613, 0x49e959fd, 0xf1553e98,
+    0x6c820621, 0xd43e6144, 0xc68bceaa, 0x7e37a9cf,
+    0xd67f4138, 0x6ec3265d, 0x7c7689b3, 0xc4caeed6,
+    0x591dd66f, 0xe1a1b10a, 0xf3141ee4, 0x4ba87981,
+    0x13cb69d7, 0xab770eb2, 0xb9c2a15c, 0x17ec639,
+    0x9ca9fe80, 0x241599e5, 0x36a0360b, 0x8e1c516e,
+    0x866616a7, 0x3eda71c2, 0x2c6fde2c, 0x94d3b949,
+    0x90481f0, 0xb1b8e695, 0xa30d497b, 0x1bb12e1e,
+    0x43d23e48, 0xfb6e592d, 0xe9dbf6c3, 0x516791a6,
+    0xccb0a91f, 0x740cce7a, 0x66b96194, 0xde0506f1
+  };
+
+}
diff --git a/src/test/org/apache/hadoop/util/TestPureJavaCrc32.java b/src/test/org/apache/hadoop/util/TestPureJavaCrc32.java
new file mode 100644
index 0000000..c476e3a
--- /dev/null
+++ b/src/test/org/apache/hadoop/util/TestPureJavaCrc32.java
@@ -0,0 +1,301 @@
+/**
+ * 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 java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.PrintStream;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Properties;
+import java.util.Random;
+import java.util.zip.CRC32;
+import java.util.zip.Checksum;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit test to verify that the pure-Java CRC32 algorithm gives
+ * the same results as the built-in implementation.
+ */
+public class TestPureJavaCrc32 {
+  private final CRC32 theirs = new CRC32();
+  private final PureJavaCrc32 ours = new PureJavaCrc32();
+
+  @Test
+  public void testCorrectness() throws Exception {
+    checkSame();
+
+    theirs.update(104);
+    ours.update(104);
+    checkSame();
+
+    checkOnBytes(new byte[] {40, 60, 97, -70}, false);
+    
+    checkOnBytes("hello world!".getBytes("UTF-8"), false);
+
+    for (int i = 0; i < 10000; i++) {
+      byte randomBytes[] = new byte[new Random().nextInt(2048)];
+      new Random().nextBytes(randomBytes);
+      checkOnBytes(randomBytes, false);
+    }
+    
+  }
+
+  private void checkOnBytes(byte[] bytes, boolean print) {
+    theirs.reset();
+    ours.reset();
+    checkSame();
+    
+    for (int i = 0; i < bytes.length; i++) {
+      ours.update(bytes[i]);
+      theirs.update(bytes[i]);
+      checkSame();
+    }
+
+    if (print) {
+      System.out.println("theirs:\t" + Long.toHexString(theirs.getValue())
+                         + "\nours:\t" + Long.toHexString(ours.getValue()));
+    }
+  
+    theirs.reset();
+    ours.reset();
+    
+    ours.update(bytes, 0, bytes.length);
+    theirs.update(bytes, 0, bytes.length);
+    if (print) {
+      System.out.println("theirs:\t" + Long.toHexString(theirs.getValue())
+                         + "\nours:\t" + Long.toHexString(ours.getValue()));
+    }
+
+    checkSame();
+    
+    if (bytes.length >= 10) {
+      ours.update(bytes, 5, 5);
+      theirs.update(bytes, 5, 5);
+      checkSame();
+    }
+  }
+
+  private void checkSame() {
+    Assert.assertEquals(theirs.getValue(), ours.getValue());
+  }
+
+  /**
+   * Generate a table to perform checksums based on the same CRC-32 polynomial
+   * that java.util.zip.CRC32 uses.
+   */
+  public static class Table {
+    private static final int polynomial = 0xEDB88320;
+
+    private final int[][] tables;
+
+    private Table(final int nBits, final int nTables) {
+      tables = new int[nTables][];
+      final int size = 1 << nBits;
+      for(int i = 0; i < tables.length; i++) {
+        tables[i] = new int[size];
+      }
+
+      //compute the first table
+      final int[] first = tables[0];
+      for (int i = 0; i < first.length; i++) {
+        int crc = i;
+        for (int j = 0; j < nBits; j++) {
+          if ((crc & 1) == 1) {
+            crc >>>= 1;
+            crc ^= polynomial;
+          } else {
+            crc >>>= 1;
+          }
+        }
+        first[i] = crc;
+      }
+
+      //compute the remaining tables
+      final int mask = first.length - 1;
+      for(int j = 1; j < tables.length; j++) {
+        final int[] previous = tables[j-1];
+        final int[] current = tables[j];
+        for (int i = 0; i < current.length; i++) {
+          current[i] = (previous[i] >>> nBits) ^ first[previous[i] & mask];
+        }
+      }
+    }
+
+    String[] toStrings(String nameformat) {
+      final String[] s = new String[tables.length];
+      for (int j = 0; j < tables.length; j++) {
+        final int[] t = tables[j];
+        final StringBuilder b = new StringBuilder();
+        b.append(String.format("  static final int[] " + nameformat
+            + " = new int[] {", j));
+        for (int i = 0; i < t.length;) {
+          b.append("\n    ");
+          for(int k = 0; k < 4; k++) {
+            b.append(String.format("0x%08X, ", t[i++]));
+          }
+        }
+        b.setCharAt(b.length() - 2, '\n');
+        s[j] = b.toString() + " };\n";
+      }
+      return s;
+    }
+
+    /** {@inheritDoc} */
+    public String toString() {
+      final StringBuilder b = new StringBuilder();
+      for(String s : toStrings(String.format("T%d_",
+          Integer.numberOfTrailingZeros(tables[0].length)) + "%d")) {
+        b.append(s);
+      }
+      return b.toString();
+    }
+
+    /** Generate CRC-32 lookup tables */
+    public static void main(String[] args) throws FileNotFoundException {
+      int i = 8;
+      final PrintStream out = new PrintStream(
+          new FileOutputStream("table" + i + ".txt"), true);
+      final Table t = new Table(i, 16);
+      final String s = t.toString();
+      System.out.println(s);
+      out.println(s);
+    }
+  }
+  
+  /**
+   * Performance tests to compare performance of the Pure Java implementation
+   * to the built-in java.util.zip implementation. This can be run from the
+   * command line with:
+   *
+   *   java -cp path/to/test/classes:path/to/common/classes \
+   *      'org.apache.hadoop.util.TestPureJavaCrc32$PerformanceTest'
+   *
+   * The output is in JIRA table format.
+   */
+  public static class PerformanceTest {
+    public static final int MAX_LEN = 32*1024*1024; // up to 32MB chunks
+    public static final int BYTES_PER_SIZE = MAX_LEN * 4;
+
+    static final Checksum zip = new CRC32(); 
+    static final Checksum[] CRCS = {new PureJavaCrc32()};
+
+    public static void main(String args[]) {
+      printSystemProperties(System.out);
+      doBench(CRCS, System.out);
+    }
+
+    private static void printCell(String s, int width, PrintStream out) {
+      final int w = s.length() > width? s.length(): width;
+      out.printf(" %" + w + "s |", s);
+    }
+
+    private static void doBench(final Checksum[] crcs, final PrintStream out) {
+      final ArrayList<Checksum> a = new ArrayList<Checksum>();
+      a.add(zip);
+      for (Checksum c : crcs)
+        if(c.getClass() != zip.getClass())
+          a.add(c);
+      doBench(a, out);
+    }
+
+    private static void doBench(final List<Checksum> crcs, final PrintStream out
+        ) {
+      final byte[] bytes = new byte[MAX_LEN];
+      new Random().nextBytes(bytes);
+
+      // Print header
+      out.printf("\nPerformance Table (The unit is MB/sec)\n||");
+      final String title = "Num Bytes";
+      printCell("Num Bytes", 0, out);
+      for (Checksum c : crcs) {
+        out.printf("|");
+        printCell(c.getClass().getSimpleName(), 8, out);
+      }
+      out.printf("|\n");
+
+      // Warm up implementations to get jit going.
+      for (Checksum c : crcs) {
+        doBench(c, bytes, 2, null);
+        doBench(c, bytes, 2101, null);
+      }
+
+      // Test on a variety of sizes
+      for (int size = 1; size < MAX_LEN; size *= 2) {
+        out.printf("|");
+        printCell(String.valueOf(size), title.length()+1, out);
+
+        Long expected = null;
+        for(Checksum c : crcs) {
+          System.gc();
+          final long result = doBench(c, bytes, size, out);
+          if(c.getClass() == zip.getClass()) {
+            expected = result;
+          } else if (result != expected) {
+            throw new RuntimeException(c.getClass() + " has bugs!");
+          }
+            
+        }
+        out.printf("\n");
+      }
+    }
+
+    private static long doBench(Checksum crc, byte[] bytes, int size,
+        PrintStream out) {
+      final String name = crc.getClass().getSimpleName();
+      final int trials = BYTES_PER_SIZE / size;
+
+      final long st = System.nanoTime();
+      crc.reset();
+      for (int i = 0; i < trials; i++) {
+        crc.update(bytes, 0, size);
+      }
+      final long result = crc.getValue();
+      final long et = System.nanoTime();
+
+      double mbProcessed = trials * size / 1024.0 / 1024.0;
+      double secsElapsed = (et - st) / 1000000000.0d;
+      if (out != null) {
+        final String s = String.format("%9.3f",  mbProcessed/secsElapsed);
+        printCell(s, name.length()+1, out);
+      }
+      return result;
+    }
+    
+    private static void printSystemProperties(PrintStream out) {
+      final String[] names = {
+          "java.version",
+          "java.runtime.name",
+          "java.runtime.version",
+          "java.vm.version",
+          "java.vm.vendor",
+          "java.vm.name",
+          "java.vm.specification.version",
+          "java.specification.version",
+          "os.arch",
+          "os.name",
+          "os.version"
+      };
+      final Properties p = System.getProperties();
+      for(String n : names) {
+        out.println(n + " = " + p.getProperty(n));
+      }
+    }
+  }
+}
-- 
1.6.0.4

