edu.stanford.math.plex

Class CRC

java.lang.Object

edu.stanford.math.plex.CRC

public class CRC
extends java.lang.Object

The CRC class provides good hash methods for int/long and string data.

Version:

$Id$

Field Summary

Fields

Modifier and Type	Field and Description
protected static int[]	hash32tab0 Internal table used by CRC code.
protected static long[]	hash64tab0 Internal table used by CRC code.
protected static long[]	hash64tab1 Internal table used by CRC code.

Method Summary

Methods

Modifier and Type	Method and Description
static int	hash32(byte[] v) Compute 32-bit CRC for an array of bytes.
static int	hash32(double[] v) Compute 32-bit CRC for an array of double.
static int	hash32(double[][] A, int rows, int cols) Compute 32-bit CRC for a matrix of doubles.
static int	hash32(float[] v) Compute 32-bit CRC for an array of float.
static int	hash32(int[] v) Compute 32-bit CRC for an array of ints.
static int	hash32(long[] v) Compute 32-bit CRC for an array of longs.
static int	hash32(long x, int initial) Easily testable function which computes 32-bit CRC for a single long.
static int	hash32(short[] v) Compute 32-bit CRC for an array of shorts.
protected static long	hash64(byte[] v) Compute 64-bit CRC for an array of bytes.
static long	hash64(double[] v) Compute 64-bit CRC for an array of double.
static long	hash64(float[] v) Compute 64-bit CRC for an array of float.
static long	hash64(int[] v) Compute 64-bit CRC for an array of ints.
static long	hash64(long[] v) Compute 64-bit CRC for an array of longs.
static long	hash64(long x, long initial) Easily testable function which computes 64-bit CRC for a single long.
static long	hash64(short[] v) Compute 64-bit CRC for an array of shorts.
static long	update_hash(int x, long hcode) Incremental 64-bit CRC for an integer.
static long	update_hash(long x, long hcode) Incremental 64-bit CRC for a long.
protected static int	update32(byte b, int hcode, int[] tbl) Incremental 32-bit CRC calculation for a single byte.
protected static int	update32(int i, int hcode, int[] tbl) Incremental 32-bit CRC calculation for a single int.
protected static int	update32(long l, int hcode, int[] tbl) Incremental 32-bit CRC calculation for a single long.
protected static int	update32(short s, int hcode, int[] tbl) Incremental 32-bit CRC calculation for a single short.
protected static int	update32l(long b, int hcode, int[] tbl) Incremental 32-bit CRC calculation for a single byte.
protected static long	update64(byte b, long hcode, long[] tbl) Incremental 64-bit CRC calculation for a single byte.
protected static long	update64(int i, long hcode, long[] tbl) Incremental 64-bit CRC calculation for a single int.
protected static long	update64(long l, long hcode, long[] tbl) Incremental 64-bit CRC calculation for a single long.
protected static long	update64(short s, long hcode, long[] tbl) Incremental 64-bit CRC calculation for a single short.
protected static long	update64l(long b, long hcode, long[] tbl) Incremental 64-bit CRC calculation for a single byte.

Methods inherited from class java.lang.Object

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

Field Detail

hash64tab0

protected static long[] hash64tab0

Internal table used by CRC code.

hash64tab1

protected static long[] hash64tab1

Internal table used by CRC code.

hash32tab0

protected static int[] hash32tab0

Internal table used by CRC code.

Method Detail

update32l

protected static int update32l(long b,
            int hcode,
            int[] tbl)

Incremental 32-bit CRC calculation for a single byte.

Parameters:

b - The next data in the CRC calculation (only lowest byte is used).

hcode - The current int result.

Returns:

Updated int value of CRC calculation.

update32

protected static int update32(byte b,
           int hcode,
           int[] tbl)

Incremental 32-bit CRC calculation for a single byte.

Parameters:

b - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated int value of CRC calculation.

update32

protected static int update32(short s,
           int hcode,
           int[] tbl)

Incremental 32-bit CRC calculation for a single short.

Parameters:

s - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated int value of CRC calculation.

update32

protected static int update32(int i,
           int hcode,
           int[] tbl)

Incremental 32-bit CRC calculation for a single int.

Parameters:

i - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated int value of CRC calculation.

update32

protected static int update32(long l,
           int hcode,
           int[] tbl)

Incremental 32-bit CRC calculation for a single long.

Parameters:

l - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated int value of CRC calculation.

update64l

protected static long update64l(long b,
             long hcode,
             long[] tbl)

Incremental 64-bit CRC calculation for a single byte.

Parameters:

b - The next data in the CRC calculation (only lowest byte is used).

hcode - The current long result.

Returns:

Updated long value of CRC calculation.

update64

protected static long update64(byte b,
            long hcode,
            long[] tbl)

Incremental 64-bit CRC calculation for a single byte.

Parameters:

b - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated long value of CRC calculation.

update64

protected static long update64(short s,
            long hcode,
            long[] tbl)

Incremental 64-bit CRC calculation for a single short.

Parameters:

s - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated long value of CRC calculation.

update64

protected static long update64(int i,
            long hcode,
            long[] tbl)

Incremental 64-bit CRC calculation for a single int.

Parameters:

i - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated long value of CRC calculation.

update64

protected static long update64(long l,
            long hcode,
            long[] tbl)

Incremental 64-bit CRC calculation for a single long.

Parameters:

l - The next data in the CRC calculation.

hcode - The current long result.

Returns:

Updated long value of CRC calculation.

hash64

protected static long hash64(byte[] v)

Compute 64-bit CRC for an array of bytes.

Parameters:

v - The byte array.

Returns:

Long containing CRC hash of array.

hash64

public static long hash64(short[] v)

Compute 64-bit CRC for an array of shorts.

Parameters:

v - The short array.

Returns:

Long containing CRC hash of array.

update_hash

public static long update_hash(int x,
               long hcode)

Incremental 64-bit CRC for an integer.

Parameters:

x - The int.

hcode - The hash so far.

Returns:

Long which is the updated hcode for x.

update_hash

public static long update_hash(long x,
               long hcode)

Incremental 64-bit CRC for a long.

Parameters:

x - The long.

hcode - The hash so far.

Returns:

Long which is the updated hcode for x.

hash64

public static long hash64(int[] v)

Compute 64-bit CRC for an array of ints.

Parameters:

v - The int array.

Returns:

Long containing CRC hash of array.

hash64

public static long hash64(float[] v)

Compute 64-bit CRC for an array of float.

Parameters:

v - The float array.

Returns:

CRC hash of array.

hash64

public static long hash64(long[] v)

Compute 64-bit CRC for an array of longs.

Parameters:

v - The long array.

Returns:

Long containing CRC hash of array.

hash64

public static long hash64(double[] v)

Compute 64-bit CRC for an array of double.

Parameters:

v - The double array.

Returns:

CRC hash of array.

hash32

public static int hash32(byte[] v)

Compute 32-bit CRC for an array of bytes.

Parameters:

v - The byte array.

Returns:

Int containing CRC hash of array.

hash32

public static int hash32(short[] v)

Compute 32-bit CRC for an array of shorts.

Parameters:

v - The short array.

Returns:

Int containing CRC hash of array.

hash32

public static int hash32(int[] v)

Compute 32-bit CRC for an array of ints.

Parameters:

v - The int array.

Returns:

Int containing CRC hash of array.

hash32

public static int hash32(float[] v)

Compute 32-bit CRC for an array of float.

Parameters:

v - The float array.

Returns:

CRC hash of array.

hash32

public static int hash32(long[] v)

Compute 32-bit CRC for an array of longs.

Parameters:

v - The long array.

Returns:

Int containing CRC hash of array.

hash32

public static int hash32(double[] v)

Compute 32-bit CRC for an array of double.

Parameters:

v - The double array.

Returns:

Int containing CRC hash of array.

hash32

public static int hash32(double[][] A,
         int rows,
         int cols)

Compute 32-bit CRC for a matrix of doubles. Used to compute a hash value for instances of Matrix.

Parameters:

A - The double[][].

rows - The length of A.

cols - The length of A[0].

Returns:

CRC hash of A.

hash64

public static long hash64(long x,
          long initial)

Easily testable function which computes 64-bit CRC for a single long.

These functions are only intended as entry points for test code. They are structurally the same as a some functions in a long-used and well-tested C library, so we were easily able to generate testcases for this code from the C code.

Parameters:

x - The long to be hashed.

initial - The CRC value to be updated.

Returns:

Long containing CRC hash value.

hash32

public static int hash32(long x,
         int initial)

Easily testable function which computes 32-bit CRC for a single long.

These functions are only intended as entry points for test code. They are structurally the same as a some functions in a long-used and well-tested C library, so we were easily able to generate testcases for this code from the C code.

Parameters:

x - The long to be hashed.

initial - The CRC value to be updated.

Returns:

Int containing CRC hash value.