Browse Prior Art Database

Air Optimized Quick Interchange Code Decoder

IP.com Disclosure Number: IPCOM000113782D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Medan, Y: AUTHOR

Abstract

This article describes a technique to optimize a Quick Interchange Code (QIC) coded stream to achieve a further compression by exploiting the statistical properties of the encoded values.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Air Optimized Quick Interchange Code Decoder

      This article describes a technique to optimize a Quick
Interchange Code (QIC) coded stream to achieve a further compression
by exploiting the statistical properties of the encoded values.

      QIC-122 is an industry standard for decoding compressed data
for 1/4 inch cartridge tape drives.  The standard defines, in a very
concise and fixed way, the format of the encoded compressed data.  It
does not however imply how compression may be achieved as long as the
encoded stream follows the standard.  There exist a number of fast
hardware implementations of QIC-122.

      The QIC-122 standard assumes that a byte-oriented input stream
is to be encoded using a mixture of direct coding stating the actual
value of the byte ('raw_byte'), and indirect coding using an offset
and a runlength values to point to a previous instance of a given
string ('compressed_byte').  The direct encoded symbol and the offset
field have a fixed-length codeword while the runlength value is
encoded using a variable-size bit-string.  The encoding format is
fixed and therefore no provisions are made in the standard to adopt
its parameters according to the context, nature and statistical
properties of the data to be encoded.

      The technique disclosed herein provides a means to further
increase the compression efficiency achieved by the QIC-122 standard
using the following enhancements:
  1.  Indirect reference table to the decoded runlength value -
  2.  Variable-size encoding of the 'raw_byte' field -

      With regard to enhancement 1, rather than using the immediate
runlength field value a...