com.cloudhopper.commons.charset

Class GSMBitPacker

java.lang.Object

com.cloudhopper.commons.charset.GSMBitPacker

public class GSMBitPacker
extends Object

Utility for packing and unpacking 8-bit to/from 7-bit byte arrays.

Author:

joelauer (twitter: @jjlauer or http://twitter.com/jjlauer)

Constructor Summary

Constructors

Constructor and Description
GSMBitPacker()

Method Summary

Methods

Modifier and Type	Method and Description
static byte[]	pack(byte[] unpacked) Pack a byte array according to the GSM bit-packing algorithm.
static byte[]	unpack(byte[] packed) Unpack a byte array according to the GSM bit-packing algorithm.

Methods inherited from class java.lang.Object

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

Constructor Detail

GSMBitPacker

public GSMBitPacker()

Method Detail

pack

public static byte[] pack(byte[] unpacked)

Pack a byte array according to the GSM bit-packing algorithm. The GSM specification defines a simple compression mechanism for its default alphabet to pack more message characters into a smaller space. Since the alphabet only contains 128 symbols, each one can be represented in 7 bits. The packing algorithm squeezes the bits for each symbol "down" into the preceeding byte (so bit 7 of the first byte actually contains bit 0 of the second symbol in a default alphabet string, bits 6 and 7 in the second byte contain bits 0 and 1 of the third symbol etc.) Since the maximum short message length is 140 bytes, you save one bit per byte using the default alphabet giving you a total of 140 + (140 / 8) = 160 characters to use. This is where the 160 character limit comes from in SMPP packets.

Having said all that, most SMSCs do NOT use the packing algorithm when communicating over TCP/IP. They either use a full 8-bit alphabet such as ASCII or Latin-1, or they accept the default alphabet in its unpacked form. As such, you will be unlikely to need this method.

Parameters:

unpacked - The unpacked byte array.

Returns:

A new byte array containing the bytes in their packed form.

unpack

public static byte[] unpack(byte[] packed)

Unpack a byte array according to the GSM bit-packing algorithm. Read the full description in the documentation of the pack method.

Parameters:

packed - The packed byte array.

Returns:

A new byte array containing the unpacked bytes.

See Also:

pack(byte[])