
Department of Computer
Science,


Telephone : 
 none  

Fax : 
 none  

email : 
p.fenwick@auckland.ac.nz 

Life Member IEEE 

After about 20 years in the Department of Computer Science (and 12 years before that in the Computer Centre) at the University of Auckland, I took early retirement from Jan 2005.
My University email and other addresses (but not telephone) should continue to be available, but will be handled less often ....
Important
notice — I am NOT
available for supervising student projects or similar
activities.
This most definitely includes internships for
foreign students, so don't even bother asking.
Enquiries
about past research may be viewed sympathetically, but by now I am
probably out of touch.
17 Dec 2015
I have been conducting occasional research since retirement. In chronological order the results are 
A general overview and cogitations on BurrowsWheeler
compression.
See Burrows–Wheeler
compression : Principles and reflections”
Theoretical
Computer Science Vol
387(2007) pp 200–219.
Abstract
After
a general description of the Burrows Wheeler Transform and a brief
survey of recent work on processing its output, the paper examines
the coding of the zeroruns from the MTF recoding stage, an aspect
with little prior treatment. It is concluded that the original
scheme proposed by Wheeler is extremely efficient and unlikely to be
much improved.
The paper then proposes some new interpretations
and uses of the Burrows Wheeler transform, with new insights and
approaches to lossless compression, perhaps including techniques
from error correction.
“PPM
Compression without Escapes”,
Software
– Practice and Experience,
online
:
25 APR 2011, DOI: 10.1002/spe.1070 ; printed Vol
42, no 2, pp 255–260, February 2012)
Abstract
A
significant cost in PPM data compression (and often the major cost)
is the provision and efficient coding of escapes while building
contexts.
This paper presents some recent work on eliminating
escapes in PPM compression, using bitwise compression with binary
contexts. It shows that PPM without escapes can achieve averages of
2.5 bits per character on the Calgary Corpus and 2.2 bpc on the
Canterbury Corpus, both values comparing well with accepted good
compressors.
A
book “Introduction
to Computer Data Representation”
Bentham
Publications 2014. It provides an introduction, from first
principles, to the internal (bitwise) representation of integers,
real numbers, characters and text, checksums and universal coding of
integers. It has about 270 pages and is available as both an
eBook(eISBN 9781608058822, 2014) and printed copy
(“PrintOnDemand” ISBN 9781608058839).
While not a
book for beginners, it is intended for reference by advanced
students and professionals.
You
may download a 1page
flier, or the
primary
link includes ordering information, the ability to download
individual chapters and a free “sample” which is the first 34
pages of each chapter or other section. The first 3 sections (which
are all free) give a good overview of the book.
“A
Note on VariableLength Codes with Constant Hamming Weights”
Journal
of Universal Computer Science, vol. 21, no. 9 (2015), 11361142 is
available at
http://www.jucs.org/jucs_21_9/a_note_on_variable.
Abstract
A
recent paper described a variablelength integer code based on the
Goldbach conjecture where every codeword had exactly 2 1bits but
with an extremely irregular structure. A later, unpublished, work
produced a much more regular code, again with a Hamming weight of 2.
This paper extends that later work to weight3 and weight4 codes,
which are shown to be competitive with moreusual codes over a
useful range of values.
Most of my papers and reports are available from here
— F I N I S —