org.lsst.ccs.utilities.image

Class FitsCheckSum

java.lang.Object

org.lsst.ccs.utilities.image.FitsCheckSum

public class FitsCheckSum
extends Object

A replacement for the FitsCheckSum implemented in nom.tam.fits.utilities.FitsCheckSum. This class is a little more flexible, specifically it allows the checksum to be accumulated across several invocations of the updateChecksum(java.nio.ByteBuffer, org.lsst.ccs.utilities.image.FitsCheckSum.Checksum) method, and allows for the DATASUM keyword to be updated after data has been changed. It also provides a method for decoding an encoded checksum.

Author:

tonyj

See Also:

FITS Checksum Proposal

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FitsCheckSum.Checksum Encapsulation of a FITS check sum.

Method Summary

Modifier and Type	Method and Description
static long	checksum(byte[] data) Calculate the Seaman-Pence 32-bit 1's complement checksum over the byte stream.
static long	checksumDecode(String encoded) Decodes an encoded checksum, the opposite of checksumEncode(long)
static String	checksumEnc(long c, boolean compl) Encode a 32bit integer according to the Seaman-Pence proposal.
static String	checksumEncode(long checksum) Encode the given checksum, including the rotating the result right by one byte.
static long	computeChecksum(ByteBuffer data) Compute a FITS check sum from a ByteBuffer
static void	setChecksum(nom.tam.fits.BasicHDU<?> hdu) Add or update the CHECKSUM keyword.
static long	updateChecksum(ByteBuffer data, FitsCheckSum.Checksum inOut) Update a check sum from a ByteBuffer
static void	updateCheckSum(nom.tam.fits.Header header, long delta) Apply an incremental update to the checksum, as a result of changing one of more records

Methods inherited from class java.lang.Object

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

Method Detail

checksum

public static long checksum(byte[] data)

Calculate the Seaman-Pence 32-bit 1's complement checksum over the byte stream. The option to start from an intermediate checksum accumulated over another previous byte stream is not implemented. The implementation accumulates in two 64-bit integer values the two low-order and the two high-order bytes of adjacent 4-byte groups. A carry-over of bits is never done within the main loop (only once at the end at reduction to a 32-bit positive integer) since an overflow of a 64-bit value (signed, with maximum at 2^63-1) by summation of 16-bit values could only occur after adding approximately 140G short values (=2^47) (280GBytes) or more. We assume for now that this routine here is never called to swallow FITS files of that size or larger. by R J Mathar Checksum.CHECKSUM

Parameters:

data - the byte sequence

Returns:

the 32bit checksum in the range from 0 to 2^32-1

Since:

2005-10-05

computeChecksum

public static long computeChecksum(ByteBuffer data)

Compute a FITS check sum from a ByteBuffer

Parameters:

data - The ByteBuffer to use as a source of data

Returns:

The computed check sum

updateChecksum

public static long updateChecksum(ByteBuffer data,
                                  FitsCheckSum.Checksum inOut)

Update a check sum from a ByteBuffer

Parameters:

data - The ByteBuffer to use as a source of data

inOut - The previously accumulated check sum, updated in place with the additional data.

Returns:

The computed check sum

checksumEnc

public static String checksumEnc(long c,
                                 boolean compl)

Encode a 32bit integer according to the Seaman-Pence proposal.

Parameters:

c - the checksum previously calculated

compl - complement the value

Returns:

the encoded string of 16 bytes.

See Also:

heasarc checksum doc

checksumEncode

public static String checksumEncode(long checksum)

Encode the given checksum, including the rotating the result right by one byte.

Parameters:

checksum -

Returns:

The encoded checksum, suitably encoded for use with the CHECKSUM header

checksumDecode

public static long checksumDecode(String encoded)

Decodes an encoded checksum, the opposite of checksumEncode(long)

Parameters:

encoded - The encoded checksum (16 character string)

Returns:

The integer checksum.

updateCheckSum

public static void updateCheckSum(nom.tam.fits.Header header,
                                  long delta)

Apply an incremental update to the checksum, as a result of changing one of more records

Parameters:

header - The header to update

delta - The change in the checksum

setChecksum

public static void setChecksum(nom.tam.fits.BasicHDU<?> hdu)
                        throws nom.tam.fits.FitsException

Add or update the CHECKSUM keyword. by R J Mathar

Parameters:

hdu - the HDU to be updated.

Throws:

nom.tam.fits.FitsException - if the operation failed

Since:

2005-10-05