com.sleepycat.je.utilint

Class Adler32

java.lang.Object

com.sleepycat.je.utilint.Adler32

All Implemented Interfaces:

Checksum

public class Adler32
extends Object
implements Checksum

Adler32 checksum implementation. This class is used rather than the native java.util.zip.Adler32 class because we have seen a JIT problem when calling the Adler32 class using the Server JVM on Linux and Solaris. Specifically, we suspect this may be Bug Parade number 4965907. See SR [#9376]. We also believe that this bug is fixed in Java 5 and therefore only use this class conditionally if we find that we're in a 1.4 JVM. [#13354]. The Adler32 checksum is discussed in RFC1950. The sample implementation from this RFC is shown below:

    #define BASE 65521  largest prime smaller than 65536
    unsigned long update_adler32(unsigned long adler,
       unsigned char *buf, int len)
    {
      unsigned long s1 = adler & 0xffff;
      unsigned long s2 = (adler >> 16) & 0xffff;
      int n;

      for (n = 0; n < len; n++) {
        s1 = (s1 + buf[n]) % BASE;
        s2 = (s2 + s1)     % BASE;
      }
      return (s2 << 16) + s1;
    }

    unsigned long adler32(unsigned char *buf, int len)
    {
      return update_adler32(1L, buf, len);
    }
 

The NMAX optimization is so that we don't have to do modulo calculations on every iteration. NMAX is the max number of additions to make before you have to perform the modulo calculation.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Adler32.ChunkingAdler32

Constructor Summary

Constructors

Constructor and Description
Adler32()

Method Summary

Modifier and Type	Method and Description
long	getValue() Returns current checksum value.
static Checksum	makeChecksum()
void	reset() Reset Adler-32 checksum to initial value.
void	update(byte[] b, int off, int len) Update current Adler-32 checksum given the specified byte array.
void	update(int b) Update current Adler-32 checksum given the specified byte.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Adler32

public Adler32()

Method Detail

makeChecksum

public static Checksum makeChecksum()

update

public void update(int b)

Update current Adler-32 checksum given the specified byte.

Specified by:

update in interface Checksum

update

public void update(byte[] b,
                   int off,
                   int len)

Update current Adler-32 checksum given the specified byte array.

Specified by:

update in interface Checksum

reset

public void reset()

Reset Adler-32 checksum to initial value.

Specified by:

reset in interface Checksum

getValue

public long getValue()

Returns current checksum value.

Specified by:

getValue in interface Checksum