steveloughran commented on code in PR #8349:
URL: https://github.com/apache/hadoop/pull/8349#discussion_r3000544644
##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/PureJavaCrc32.java:
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@@ -17,78 +17,21 @@
*/
package org.apache.hadoop.util;
-import java.util.zip.Checksum;
+import java.util.zip.CRC32;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
- * 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
+ * The legacy PureJavaCrc32 implemented in HADOOP-6148 is
+ * much slower than JDK native implementation in modern JDKs,
+ * HADOOP-19839 rewrites it to delegate to JDK native CRC32.
*
* @see java.util.zip.CRC32
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
-public class PureJavaCrc32 implements Checksum {
-
- /** the current CRC value, bit-flipped */
- private int crc;
-
- /** Create a new PureJavaCrc32 object. */
- public PureJavaCrc32() {
- reset();
- }
-
- @Override
- public long getValue() {
- return (~crc) & 0xffffffffL;
- }
-
- @Override
- public void reset() {
- crc = 0xffffffff;
- }
-
- @Override
- public void update(final byte[] b, final int offset, final int len) {
- int localCrc = crc;
-
- final int remainder = len & 0x7;
- int i = offset;
- for(final int end = offset + len - remainder; i < end; i += 8) {
- final int x = localCrc
- ^ ((((b[i ] << 24) >>> 24) + ((b[i+1] << 24) >>> 16))
- + (((b[i+2] << 24) >>> 8 ) + (b[i+3] << 24)));
-
- localCrc = ((T[((x << 24) >>> 24) + 0x700] ^ T[((x << 16) >>> 24) +
0x600])
- ^ (T[((x << 8) >>> 24) + 0x500] ^ T[ (x >>> 24) +
0x400]))
- ^ ((T[((b[i+4] << 24) >>> 24) + 0x300] ^ T[((b[i+5] << 24) >>>
24) + 0x200])
- ^ (T[((b[i+6] << 24) >>> 24) + 0x100] ^ T[((b[i+7] << 24) >>>
24)]));
- }
-
- /* loop unroll - duff's device style */
- switch(remainder) {
- case 7: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 6: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 5: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 4: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 3: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 2: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- case 1: localCrc = (localCrc >>> 8) ^ T[((localCrc ^ b[i++]) << 24) >>>
24];
- default:
- /* nothing */
- }
-
- // Publish crc out to object
- crc = localCrc;
- }
+public class PureJavaCrc32 extends CRC32 {
Review Comment:
Deprecate it in code and say "just use java.util.zip.CRC32" if targeting
hadoop 3.5+
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