edu.iris.dmc.seedcodec

Class Steim1

java.lang.Object

edu.iris.dmc.seedcodec.Steim1

public class Steim1
extends java.lang.Object

Class for decoding or encoding Steim1-compressed data blocks to or from an array of integer values.

Steim compression scheme Copyrighted by Dr. Joseph Steim.

Reference material found in:

Appendix B of SEED Reference Manual, 2nd Ed., pp. 119-125 Federation of Digital Seismic Networks, et al. February, 1993

Coding concepts gleaned from code written by:

Guy Stewart, IRIS, 1991

Tom McSweeney, IRIS, 2000

Constructor Summary

Constructors

Constructor and Description
Steim1()

Method Summary

Methods

Modifier and Type	Method and Description
static int[]	decode(byte[] b, int numSamples, boolean swapBytes) Abbreviated, zero-bias version of decode().
static int[]	decode(byte[] b, int numSamples, boolean swapBytes, int bias) Decode the indicated number of samples from the provided byte array and return an integer array of the decompressed values.
static SteimFrameBlock	encode(int[] samples, int frames) Abbreviated zero-bias version of encode().
static SteimFrameBlock	encode(int[] samples, int frames, int bias) Encode the array of integer values into a Steim 1 * compressed byte frame block.
static SteimFrameBlock	encode(int[] samples, int frames, int bias, int offset)
protected static int[]	extractSamples(byte[] bytes, int offset, boolean swapBytes) Extracts differences from the next 64 byte frame of the given compressed byte array (starting at offset) and returns those differences in an int array.
static void	main(java.lang.String[] args) Static method for testing the decode() method.

Methods inherited from class java.lang.Object

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

Constructor Detail

Steim1

public Steim1()

Method Detail

decode

public static int[] decode(byte[] b,
           int numSamples,
           boolean swapBytes,
           int bias)
                    throws SteimException

Decode the indicated number of samples from the provided byte array and return an integer array of the decompressed values. Being differencing compression, there may be an offset carried over from a previous data record. This offset value can be placed in bias, otherwise leave the value as 0.

Parameters:

b - input byte array to be decoded

numSamples - the number of samples that can be decoded from array b

swapBytes - if true, swap reverse the endian-ness of the elements of byte array b.

bias - the first difference value will be computed from this value. If set to 0, the method will attempt to use the X(0) constant instead.

Returns:

int array of length numSamples.

Throws:

SteimException - - encoded data length is not multiple of 64 bytes.

decode

public static int[] decode(byte[] b,
           int numSamples,
           boolean swapBytes)
                    throws SteimException

Abbreviated, zero-bias version of decode().

Throws:

SteimException

See Also:

edu.iris.Fissures.codec.Steim1#decode(byte[],int,boolean,int)

encode

public static SteimFrameBlock encode(int[] samples,
                     int frames,
                     int bias)
                              throws SteimException

Encode the array of integer values into a Steim 1 * compressed byte frame block. This algorithm will not create a byte block any greater * than 63 64-byte frames. frames represents the number of frames to be written. This number should be determined from the desired logical record length minus the data offset from the record header (modulo 64) If samples is exhausted before all frames are filled, the remaining frames will be nulls. bias is a value carried over from a previous data record, representing X(-1)...set to 0 otherwise

Parameters:

samples - the data points represented as signed integers

frames - the number of Steim frames to use in the encoding

bias - offset for use as a constant for the first difference, otherwise set to 0

Returns:

SteimFrameBlock containing encoded byte array

Throws:

SteimException - samples array is zero size

SteimException - number of frames is not a positive value

SteimException - cannot encode more than 63 frames

encode

public static SteimFrameBlock encode(int[] samples,
                     int frames,
                     int bias,
                     int offset)
                              throws SteimException

Throws:

SteimException

encode

public static SteimFrameBlock encode(int[] samples,
                     int frames)
                              throws SteimException

Abbreviated zero-bias version of encode().

Throws:

SteimException

See Also:

edu.iris.Fissures.codec.Steim1#encode(int[],int,int)

extractSamples

protected static int[] extractSamples(byte[] bytes,
                   int offset,
                   boolean swapBytes)

Extracts differences from the next 64 byte frame of the given compressed byte array (starting at offset) and returns those differences in an int array. An offset of 0 means that we are at the first frame, so include the header bytes in the returned int array...else, do not include the header bytes in the returned array.

Parameters:

bytes - byte array of compressed data differences

offset - index to begin reading compressed bytes for decoding

swapBytes - reverse the endian-ness of the compressed bytes being read

Returns:

integer array of difference (and constant) values

main

public static void main(java.lang.String[] args)
                 throws SteimException

Static method for testing the decode() method.

Parameters:

args - not used

Throws:

SteimException - from called method(s)