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Signed-magnitude: The integer representation of choice for IoT?
What is the best representation to use for integer values in a binary computer? I’m guessing that most people think two’s complement is the answer, because this is the representation that all the computers they know about use (the Univac 1100/2200 series uses one’s complement; I don’t know of any systems currently in use that make use of signed magnitude, pointers welcome).
The C Standard allows implementations to support two’s complement, one’s complement and signed magnitude (the Univac 1100/2200 series has a C compiler). Is it time for the C Standard to drop support for one’s complement and signed magnitude?.
Why did two’s complement ‘win’ the integer representation battle and what are the chances that hardware vendors are likely to want to use a different representation in the future?
The advantage of two’s complement over the other representations is that the same hardware circuits can be used to perform arithmetic on unsigned and signed integer values. Not a big issue these days, but a major selling point back when chip real-estate was limited.
I can think of one market where signed magnitude is the ‘best representation’, extremely low power devices, such as those that extract power from the radio waves permeating the environment, or from the vibrations people generate as they move around.
Most of the power consumed by digital devices occurs when a bit flips from zero to one, or from one to zero. An application that spends most of its time processing signals that vary around zero (i.e., can have positive and negative values) will experience many bit flips, using a two’s complement representation, when the value changes from positive to negative, or vice-versa, e.g., from 0000000000000001 to 0000000000000000 to 1111111111111111; in signed magnitude a change of sign generates one extra bit-flip, e.g., 0000000000000001 to 0000000000000000 to 1000000000000001.
Simulations show around 30% few transitions for signed magnitude compared with two’s complement, for certain kinds of problems.
Signed magnitude would appear to be the integer representation of choice for some Internet-of-Things solutions.
Software systems are the product of cognitive capitalism
Economics obviously has a significant impact on the production of software systems; it is the second chapter of my empirical software engineering book (humans, who are the primary influencers, are the first chapter; technically the Introduction is the first chapter, but you know what I mean).
I have never been happy with the chapter title “Economics”; it does not capture the spirit of what I want to talk about. Yes, a lot of the technical details covered are to be found in economics related books and courses, but how do these technical details fit into a grand scheme?
I was recently reading the slim volume “Dead Man Working” by Cederström and Fleming and the phrase cognitive capitalism jumped out at me; here was a term that fitted the ideas I had been trying to articulate. It took a couple of days before I took the plunge and changed the chapter title. In the current draft pdf little else has changed in the ex-Economics chapter (e.g., a bit of a rewrite of the first few lines), but now there is a coherent concept to mold the material around.
Ecosystems chapter added to “Empirical software engineering using R”
The Ecosystems chapter of my Empirical software engineering book has been added to the draft pdf (download here).
I don’t seem to be able to get away from rewriting everything, despite working on the software engineering material for many years. Fortunately the sparsity of the data keeps me in check, but I keep finding new and interesting data (not a lot, but enough to slow me down).
There is still a lot of work to be done on the ecosystems chapter, not least integrating all the data I have been promised. The basic threads are there, they just need filling out (assuming the promised data sets arrive).
I did not get any time to integrate in the developer and economics data received since those draft chapters were released; there has been some minor reorganization.
As always, if you know of any interesting software engineering data, please tell me.
I’m looking to rerun the workshop on analyzing software engineering data. If anybody has a venue in central London, that holds 30 or so people+projector, and is willing to make it available at no charge for a series of free workshops over several Saturdays, please get in touch.
Projects chapter next.
2017 in the programming language standards’ world
Yesterday I was at the British Standards Institution for a meeting of IST/5, the committee responsible for programming languages.
The amount of management control over those wanting to get to the meeting room, from outside the building, has increased. There is now a sensor activated sliding door between the car-park and side-walk from the rear of the building to the front, and there are now two receptions; the ground floor reception gets visitors a pass to the first floor, where a pass to the fifth floor is obtained from another reception (I was totally confused by being told to go to the first floor, which housed the canteen last time I was there, and still does, the second reception is perched just inside the automatic barriers to the canteen {these barriers are also new; the food is reasonable, but not free}).
Visitors are supposed to show proof that they are attending a meeting, such as a meeting calling notice or an agenda. I have always managed to look sufficiently important/knowledgeable/harmless to get in without showing any such documents. I was asked to show them this time, perhaps my image is slipping, but my obvious bafflement at the new setup rescued me.
Why does BSI do this? My theory is that it’s all about image, BSI is the UK’s standard setting body and as such has to be seen to follow these standards. There is probably some security standard for rules to follow to prevent people sneaking into buildings. It could be argued that the name British Standards is enough to put anybody off wanting to enter the building in the first place, but this does not sound like a good rationale for BSI to give. Instead, we have lots of sliding doors/gates, multiple receptions (I suspect this has more to do with a building management cat fight over reception costs), lifts with no buttons ‘inside’ for selecting floors, and proof of reasons to be in the building.
There are also new chairs in the open spaces. The chairs have very high backs and side-baffles that surround the head area, excellent for having secret conversations and in-tune with all the security. These open areas are an image of what people in the 1970s thought the future would look like (BSI is a traditional organization after all).
So what happened in the meeting?
Cobol standard’s work becomes even more dead. PL22.4, the US Cobol group is no more (there were insufficient people willing to pay membership fees, so the group was closed down).
People are continuing to work on Fortran (still the language of choice for supercomputer Apps), Ada (some new people have started attending meetings and support for @ is still being fought over), C, Internationalization (all about character sets these days). Unprompted somebody pointed out that the UK C++ panel seemed to be attracting lots of people from the financial industry (I was very professional and did not relay my theory that it’s all about bored consultants wanting an outlet for their creative urges).
SC22, the ISO committee responsible for programming languages, is meeting at BSI next month, and our chairman asked if any of us planned to attend. The chair’s response, to my request to sell the meeting to us, was that his vocabulary was not up to the task; a two-day management meeting (no technical discussions permitted at this level) on programming languages is that exciting (and they are setting up a special reception so that visitors don’t have to go to the first floor to get a pass to attend a meeting on the ground floor).
Information on computers from the 1970s and earlier
A collection of links to sources of hardware and software related information from the 1970s and earlier.
Computers and Automation, a monthly journal published between 1954 and 1978, by far and away the best source of detailed information from this period. The June issue contained an extensive computer directory and buyers guide, including a census of installed computers. The collected census for 1962-1974 must rank in the top ten of pdf files that need to be reliably converted to text.
Computer characteristics quarterly, the title says it all; the stories about the weird and wonderful computers that used to be on sale really are true. Only a couple of issues available online at the moment.
Bitsavers huge collection of scanned computer manuals. The directory listing of computer companies is a resource in its own right.
DTIC (Defense Technical Information Center). A treasure trove of work sponsored by the US military from the time of Rome and late.
Ed Thelan’s computer history: note his contains material that can be hard to find via the main page, e.g., the BRL 1961 report.
“Inventory of Automatic data processing equipment in the Federal Government”: There are all sorts of interesting documents lurking in pdfs waiting to be found by the right search query.
Books
“Software Reliability” by Thayer, Lipow and Nelson is now available online.
“The Economics of Computers” by William F. Sharpe contains lots of analysis and data on computer purchase/leasing and usage/performace details from the mid-1960s.
“Data processing technology and economics” by Montgomery Phister is still only available in dead tree form (and uses up a substantial amount of tree).
“Handbook of Automation Computation and Control Volume 2”
“Foundations of computer programming in Britain, 1945-55”, M. Campbell-Kelly’s PhD thesis (freely downloadable from the British Library; registration required).
Reports
Computers in Spaceflight The NASA Experience covers computers used in spacecraft up to the mid 1980s.
History of NSA General-Purpose Electronic Digital Computers (written in 1964, declassified in 2004).
Missing in Action
“A Study of Technological Innovation: The Evolution of Digital Computers”, Kenneth Knight’s PhD thesis at Carnegie Institute of Technology, published in 1963. Given Knight’s later work, this will probably be a very interesting read.
“Computer Survey”, compiled by Mr Peddar, was a quarterly list of computers installed in the UK. It relied on readers (paper) mailing in details of computers in use. There are a handful of references and that’s all I can find.
What have I missed? Suggests and links very welcome.
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