nom.tam.fits.utilities

Class FitsCheckSum

java.lang.Object

nom.tam.fits.utilities.FitsCheckSum

public final class FitsCheckSum
extends Object

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 String	checksumEnc(long c, boolean compl) Encode a 32bit integer according to the Seaman-Pence proposal.
static void	setChecksum(BasicHDU<?> hdu) Add or update the CHECKSUM keyword.

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

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

setChecksum

public static void setChecksum(BasicHDU<?> hdu)
                        throws FitsException

Add or update the CHECKSUM keyword. by R J Mathar

Parameters:

hdu - the HDU to be updated.

Throws:

FitsException - if the operation failed

Since:

2005-10-05