Riscyforth: the work goes on

So after my last post somebody give me a “very poor” vote – I am consoling myself with the idea that was because they are really very keen for an assembly-based Forth to run on their RISC-V SBC and not because they thought it was an incoherent ramble.

In any case I have continued to work on Riscyforth – adding to its functionality and edging closer all the time to matching the Forth standard – getting close enough now to describe it as “Forth” and not just “Forth-like”.

Eight months ago, when I started, reading an online copy of “Threaded Interpretive Languages” which promised you could write your own TIL in a few weeks, I never considered using anything other than assembly to write it – just because I’m so old I thought that’s was the whole point of Forth – an interpreted language but written in machine code for speed.

I’ve learnt a lot on the way: including not to believe you can get from scratch to writing a working language in a few weeks – especially not in the world of virtual memory. Though I dare say, in the extremely unlikely event of someone commissioning me to write them a Forth from the ground up, I wouldn’t take eight months to get this far either next time.

One thing I have definitely learnt is the power and importance of unit testing – it matters quite a lot when you are putting together something on your own and can often make one assumption too many – a decent unit test soon clears you of that misapprehension.

What I haven’t got includes any users (never mind co-developers) or any useful or interesting programs.

On the former, RISC-V single board computers (SBCs) were promised to be widely available just about now, but the cancelling of the Beagle V project means that the more expensive Nezha is all that’s out there for now (I have one and it’s what is running in the image above). Compared to the ultra-cheap ARM boards (or even the high-end examples like some of the Raspberry Pi SBC kits) it’s fair to say RISC-V is not yet at the races, and the only users are likely to be people like me – hoping and waiting for the revolution to get here.

I picked Forth because the hope was it would give the first generation of RISC-V SBC hackers an easy way to get at their hardware and that is still the case, but there has to be some hardware to get at.

So I still have the sense I am working away on something that nobody else might ever want to use (the fact that it’s written in assembly also makes it fundamentally non-portable – I just cannot say ‘oh well let’s switch to the Raspberry Pi’!).

But if you are interested, current features of Riscyforth include:

• Support for deeply nested loops and conditionals
• Write your own words using : and ; (ie it is easy to extend the language by writing secondary words out of the existing primary words)
• A custom memory allocator for arbitrary blocks of memory
• Support for VARIABLE and CONSTANT
• All (or almost all?) the stack operations you would expect
• Hex, octal, decimal and binary support

The main thing currently missing is support for CREATE and a data space, but now I’ve grappled with the memory allocator (for general memory allocation) I will move on that. The listing of the test file might give you some ideas of what’s there, but even that is now behind where the code base is (yes, I know this isn’t how test-based development is meant to work!)

\ Unit tests


\ Stack operations tests

: testOVER2
." Testing OVER2 " 5 SPACES
10 30 50 90 70 OVER2
50 = SWAP 30 = AND IF ." OVER2 passed " else ." OVER2 FAILED " then cr
;

: testDrop2
." Testing DROP2 " 5 spaces
99 2 3 4
drop2
2 = if ." DROP2 passed " else ." DROP2 FAILED " then cr
;

: testSquare
." Testing SQUARE " 5 spaces
7 square
49 = if ." SQUARE passed " else ." SQUARE FAILED " then cr
;

: testCube
." Testing CUBE " 5 spaces
5 cube
125 = if ." CUBE passed " else ." CUBE FAILED " then 5 spaces
3 cube
28 = if ." CUBE FAILED " else ." CUBE passed " then cr
;

: testNIP2
." Testing NIP2 " 5 spaces
10 20 30 40 50 NIP2
50 = SWAP 40 = AND SWAP 10 = AND if ." NIP2 passed " else ." NIP2 FAILED " then cr 
;

: testDUP2
." Testing DUP2 " 5 SPACES
900 800 700 DUP2
700 = SWAP 800 = AND SWAP 700 = AND SWAP 800 = AND if ." DUP2 passed" else ." DUP2 FAILED " then cr
;

: testtuck2
." Testing TUCK2 " 5 spaces
1 2 3 4 5 6 TUCK2
6 = swap 5 = and swap 4 = and swap 3 = and swap 6 = and swap 5 = and if ." TUCK2 passed" else ." TUCK2 FAILED " then cr
;

: testswap2
." Testing SWAP2 " 5 spaces
1 2 3 4 5 6 7 8 SWAP2
6 = swap 5 = and swap 8 = and if ." SWAP2 passed " else ." SWAP2 FAILED " then cr
;

: testrot2
." Testing ROT2 " 5 spaces
99 2 3 4 5 6 ROT2
2 = swap 99 = and swap 6 = and if ." ROT2 passed " else ." ROT2 FAILED " then cr
;

: TESTDUP
." Testing DUP " 5 spaces
34 45 DUP
45 = SWAP 45 = AND swap 34 = AND IF ." DUP passed " else ." DUP FAILED " then cr ;

: TESTBL
." Testing BL" 5 spaces BL 32 = if ." BL passed " else ." BL FAILED " then cr ;

: TESTDEPTH
." Testing DEPTH" 5 spaces
depth dup 0 < IF ." WARNING: Stack in negative territory " THEN 10 20 rot depth swap - 3 = IF ." DEPTH passed " ELSE ." DEPTH FAILED " then cr ;

: TESTINVERT
." Testing INVERT " 5 spaces
-1 INVERT IF ." INVERT FAILED " ELSE hex 0xF0F0F0F00F0F0F35 INVERT 0xF0F0F0FF0F0F0CA = IF ." INVERT passed " ELSE ." INVERT FAILED " then then decimal cr ;

\ Basic tests

: VERIFYTYPEPROMPT
." Verifying TYPEPROMPT " cr
TYPEPROMPT cr
;

: VERIFYGETNEXTLINE_IMM
." Verifying GETNEXTLINE_IMM - please press RETURN only " cr
GETNEXTLINE_IMM cr
;

: VERIFYOK
." Verifying OK " cr
OK cr
;

: VERIFYTOKENIZE_IMM
." Verifying TOKENIZE_IMM " cr
TOKENIZE_IMM
;

: VERIFYSEARCH
." Verifying SEARCH " cr
SEARCH
;

: TESTHEX
." Testing HEX " 5 SPACES
HEX 0x10 0xFF + DUP
0x10F = IF ." HEX passed with output 0x10F = " . ELSE ." HEX FAILED with output 0x10F =  " . then cr
\ ensure other tests keep testdup2
DECIMAL
;

: TESTDECIMAL
." Testing DECIMAL " 5 SPACES
DECIMAL 20 DUP
20 = IF ." DECIMAL passed wth output 20 = " DUP . ." = " HEX . DECIMAL ELSE ." DECIMAL FAILED with output 20 = " DUP . ." = " HEX . DECIMAL THEN CR
;

: TESTOCTAL 
." Testing OCTAL " 5 SPACES OCTAL 20 DUP DECIMAL 16 = IF ." OCTAL passed with output 20o = " DUP OCTAL . ." = " DECIMAL .
ELSE ." OCTAL FAILED with 20o = " DUP OCTAL . ." = " DECIMAL . THEN CR ;

: VERIFYBINARY 
." Verifying BINARY  - " 1 2 4 8 16 32 64 128 256 512
BINARY ." powers of 2 from 9 to 0 in binary... " cr
. cr . cr . cr . cr . cr . cr . cr . cr . cr . cr DECIMAL ;

: VERIFYDOT
." Verifying DOT " 5 spaces 0 1 2 3 4 5
." ... should see countdown from 5 to 0: " . . . . . . CR ;

: TESTADD
." Testing ADD " 5 SPACES 900 -899 +
IF ." ADD passed " ELSE ." ADD FAILED " THEN CR ;

: testMUL
." Testing MUL " 5 spaces
5 5 5 * *
5 cube
= if ." MUL passed " else ." MUL FAILED " then cr
;

: TESTDIV
." Testing DIV " 5 SPACES 99 11 / 101 11 / * 81 =
IF ." DIV passed " else ." DIV FAILED " then cr ;

: TESTSUB
." Testing SUB " 5 spaces 
75 22 - 53 = IF ." SUB passed " else ." SUB FAILED " then cr ;

: TESTPLUS1
." Testing 1+ " 5 SPACES
10 1+ 11 = IF ." 1+ passed " ELSE ." 1+ FAILED " THEN CR ;

: TESTPLUS2
." Testing 2+ " 5 SPACES
10 2+ 12 = IF ." 2+ passed " ELSE ." 2+ FAILED " THEN CR ;

: TESTMINUS1
." Testing 1- " 5 spaces
-1 1- -2 = IF ." 1- passed " ELSE ." 1- FAILED " THEN CR ;

: TESTMINUS2
." Testing 2- " 5 SPACES
10 2- 8 = IF ." 2- passed " ELSE ." 2- FAILED " THEN CR ;

: TESTUNDERPLUS
." Testing UNDERPLUS" 5 spaces
10 15 20 underplus 30 = if ." UNDERPLUS passed" else ." UNDERPLUS FAILED" then cr ;

: TESTMOD
." Testing MOD" 5 spaces
13 7 mod 6 = if ." MOD passed" else ." MOD FAILED" then cr ;

: TESTSLMOD
." Testing /MOD" 5 spaces
13 7 /mod 1 = swap 6 = and if ." /MOD passed " else ." /MOD FAILED" then cr ;

: TESTNEGATE
." Testing NEGATE" 5 spaces 13 negate -13 =
if ." NEGATE passed" else ." NEGATE FAILED" then cr ;

: TESTABS
." Testing ABS" 5 spaces -13 abs 13 =
if ." ABS passed" else ." ABS FAILED" then cr ;

: TESTMINMAX
." Testing MAX and MIN" 5 spaces
20 10 dup2 MAX 20 = if ." MAX passed and " else ." MAX FAILED and " then min 10 = if ." MIN passed." else ." MIN FAILED." then cr ;

: TESTSHIFTS
." Testing LSHIFT and RSHIFT" 5 spaces
10 4 lshift 160 = IF ." LSHIFT passed " ELSE ." LSHIFT FAILED " then 48 2 rshift 12 = if ." RSHIFT passed " ELSE ." RSHIFT FAILED " THEN cr ;


: VERIFYWORDLIST 
." Verifying WORDS .... " WORDS CR ;

: TESTLITERALNUMB 
." Testing LITERALNUMB .... " 213 213 = IF ." LITERALNUMB passed " ELSE ." LITERALNUMB FAILED " THEN CR ;

: TESTVARIABLE 
." Testing VARIABLE and VARIN (and @ and !)" 5 SPACES
VARIABLE OLDGEEZER 901 OLDGEEZER ! OLDGEEZER DUP @ 1+ SWAP ! OLDGEEZER @ 902 =
IF ." VARIABLE, VARIN, @ and ! passed " ELSE ." VARIABLE, VARIN, @ and ! FAILED " THEN CR ;

: TESTCONSTANT
." Testing CONSTANT " 5 SPACES
365 CONSTANT DAYS 7 CONSTANT WEEK DAYS WEEK / 52 = IF -3 CONSTANT NEGNUMB NEGNUMB WEEK + 4 = IF ." CONSTANT passed " ELSE ." CONSTANT FAILED " THEN CR ELSE ." CONSTANT has FAILED " THEN CR ;

: TESTTYPE 
." Verifying GETLINE, TYPE and TIB " CR ." Please enter some text to be echoed back. " CR
GETLINE CR ." Echoing... " TIB SWAP TYPE CR ;

: TESTCHAR
." Testing CHAR" 5 spaces
char Z 90 = IF char z 122 = IF ." CHAR passed " else ." CHAR FAILED " then else ." CHAR FAILED " THEN cr ;

: VERIFYSOURCE 
." Verifying SOURCE" 5 spaces
source type cr ;

\ Test if else then
: TESTCONDITIONALS 
." Testing IF ... ELSE ... THEN conditionals. " CR
1 if ." Simple IF passed " else ." Simple IF FAILED " then cr
0 1 if ." Testing nested IF... " if ." Nested IF FAILED " else ." Nested IF passed " then 5 5 * . then ." = 25 " cr
1 0 if ." Failed a final test of IF " else ." A final test of IF ... " if ." is passed " else ." is FAILED " then then cr ;

\ Stuff to test EXIT
: EXITTEST1
EXIT ." If you see this EXIT FAILED " CR ;
: EXITTEST2
VARIABLE EXITVAR 200 EXITVAR ! ;
: EXITTEST3
EXITVAR DUP @ 1+ SWAP ! EXITVAR DUP @ 1+ SWAP ! EXIT EXITVAR DUP @ 1+ SWAP ! ;

: TESTEXIT
." Testing EXIT " 5 SPACES EXITTEST1
EXITTEST2 EXITTEST3 EXITVAR @ 202 = IF ." EXIT passed " ELSE ." EXIT FAILED " THEN CR ;

\ Test return stack words

: TESTRSTACKBASICS
." Testing >R, R@ and R> along with RDROP" cr
34 35 36 >R >R >R R@ 34 = RDROP R@ 35 = AND RDROP R@ 36 = AND RDROP if ." >R, R@ and RDROP passed " else ." >R, R@ and RDROP FAILED" then cr
99 >R R> 99 = if ." R> passed " else ." R> FAILED " then cr ;

\ loop
: TESTBEGINEND
." Testing BEGIN ... END loop " 5 SPACES
32 BEGIN DUP EMIT 1+ DUP 127 > END ."  BEGIN ... END passed " CR ;

: TESTBEGINWHILE
." Testing BEGIN ... WHILE " 5 spaces
32 BEGIN DUP space hex . space decimal DUP 100 < IF DUP EMIT 1+ ELSE DUP 32 - EMIT 1+ WHILE DUP 110 = END ."  BEGIN ... WHILE passed " cr ;

: TESTDOLOOP
." Testing DO ... LOOP " 5 spaces
1 10 1 DO DUP 1+ LOOP 10 = IF ." DO ... LOOP passed" ELSE ." DO ... LOOP FAILED" THEN CR ;

: TESTPLUSLOOP
." Testing DO .... +LOOP" 5 SPACES
1 100  1 DO DUP 1+ 101 +LOOP 2 = IF ." DO ... +LOOP passed" ELSE ." DO .... +LOOP FAILED" THEN CR ;

: VERIFYIJ
." Verifying I and J in nested loops" CR
10 0 DO 10 0 DO ." ( "  J . ." , " I . ." ) " LOOP CR LOOP
." I and J verified" CR ; 

: VERIFYLEAVE
." Verifying LEAVE and UNLOOP " CR
10 0 DO 10 0 DO J I > J I = OR IF ." ( "  J . ." , " I . ." ) " ELSE UNLOOP LEAVE 3 0 DO LOOP 3 0 DO LOOP 3 0 DO LOOP THEN LOOP CR LOOP
." LEAVE and UNLOOP verified" CR ;


\ Testing memory functions
: ZZ ." ', EXECUTE and C! passed " ;

: TESTINGTICK 
." Testing ', EXECUTE and C! " 5 spaces
hex 0x58 decimal ' ZZ 24 + C! ' XZ execute cr
\ Change back or else subsequent tests will break
." Testing one more time " 5 spaces
hex 0x5A decimal ' xz 24 + C! ' zZ exeCUTE  cr ;

: testcfetch 
." Testing C@" 5 spaces
' XOR 24 + c@ 88 = if ." C@ passed " else ." C@ FAILED " then cr ;

\ Dummy words to use in MOVE test
: ZM * ;
: ZD / ;
: reup decimal 68 ' ZM 25 + C! ;

: TESTINGMOVE
." Testing MOVE " 5 spaces
10 10 ZM 100 = IF ' ZM 24 + ' ZD 24 + 24 move 100 2 ' ZM execute 50 = IF ." MOVE passed " else ." MOVE FAILED " then cr else ." Test failure " then reup ;

: TESTFETCH
." Testing @ (and BASE)" 5 spaces
octal base @ 10 = hex base @ 0x10 = AND decimal base @ 10 = AND if ." @ and BASE passed" ELSE ." @ and BASE FAILED" then cr ;

: TESTPLUSSTORE
." Testing +! " 5 SPACES ' ZM 24 + -1  SWAP +! 5 5 ' YM EXECUTE 25 = IF ." +! passed " ELSE ." +! FAILED " THEN 2 SPACES
' YM 24 + 1 SWAP ' +! execute 5 5 ' ZM EXECUTE 25 = INVERT IF ." +! address find FAILED " THEN  CR ;

: TESTPADFILLERASE
." Testing PAD, FILL and ERASE " 5 SPACES
PAD 10 35 FILL PAD 3 + 1 ERASE PAD 2 + C@ 35 = PAD 3 + C@ 0 = AND PAD 4 + C@ 35 = AND IF ." PAD, FILL and ERASE passed" ELSE ." PAD, FILL and ERASE FAILED" THEN CR ;

\ Test groupings

\ Memory tests
: TESTMEMORY
." Testing memory manipulation words" cr
TESTINGTICK testcfetch testingmove testchar testfetch testplusstore TESTPADFILLERASE
." Testing of memory code complete" cr ;

\ Test loops
: TESTLOOPS
." Running tests of looping " cr
TESTBEGINEND testbeginwhile TESTDOLOOP TESTPLUSLOOP VERIFYIJ VERIFYLEAVE
." Testing of loops complete" CR ;

\ Test Rstack
: RSTACKTESTS
." Testing return stack" cr
testrstackbasics 
." Testing return stack complete" cr ;

\ Test listwords
: LISTWORDSTESTS
." Running 'listwords' group of tests " CR
VERIFYWORDLIST TESTLITERALNUMB TESTVARIABLE TESTTYPE
VERIFYSOURCE TESTCONSTANT
." 'listwords' group of tests complete " CR ;

\ Test integer
: INTEGERTESTS
." Running integer tests " cr
TESTADD TESTMUL TESTDIV TESTSUB TESTPLUS1 TESTMINUS1
TESTminus2 testplus2 testunderplus testminmax testmod testslmod testabs testnegate testshifts
." Integer tests complete " CR
;

\ Group of stack operations tests
: STACKOPTESTS
." Running stackop tests " cr
TESTOVER2
testDrop2 testSquare
testCube
testNIP2 testDUP2
testtuck2 testswap2 testrot2 testdup testbl testdepth
testinvert
." stackop tests over " cr
;

\ Group of Basics tests
: BASICSTESTS
." Running basics tests and verifications " cr
VERIFYTYPEPROMPT
VERIFYGETNEXTLINE_IMM
VERIFYOK
VERIFYTOKENIZE_IMM 
VERIFYSEARCH OK
." ***Any error message above can almost certainly be ignored*** " CR
TESTHEX TESTDECIMAL TESTOCTAL VERIFYBINARY TESTEXIT
." Verifying ENCSQ with this output " cr
." Verifying COMMENT " cr \ ." COMMENT verification FAILED " 
VERIFYDOT
." Basics tests and verifications over " cr
;


\ Run all the tests
: UTS
DECIMAL
." Running unit tests " cr
STACKOPTESTS
." Press enter to continue " GETLINE CR
BASICSTESTS
." Press enter to continue " GETLINE CR
INTEGERTESTS
." Press enter to continue " GETLINE CR
LISTWORDSTESTS
." Press enter to continue " GETLINE CR
TESTCONDITIONALS
." Press enter to continue " GETLINE CR
RSTACKTESTS
." Press enter to continue " GETLINE CR
TESTLOOPS
." Press enter to continue " GETLINE CR
TESTMEMORY
." Press enter to continue " GETLINE CR
 ABORT" Verifying ABORTCOMM and leaving tests with this message "  ." ABORTCOMM has FAILED"
;

A moment of doubt?

I have been working on Riscyforth, my Forth-like language for RISC-V single board computers (SBCs) for seven months now.

When I started there weren’t even any (affordable) SBCs available. Now there is one (which is really just an evaluation board) and the mass market is still not here – so it’s not as if I am seriously lagging behind.

But I am wondering if I should keep going.

In truth progress on the project is accelerating. I have a better idea of what I am doing and I am writing better assembly than I was back in December.

But partly that is the problem – because I can also understand that just writing some assembly code to shave off a few cycles (maybe) compared to the C-based alternatives like Gforth isn’t really enough.

For while I have now got to the point where I can write and load external programs in what is (almost) Forth – and spent the whole of last week debugging issues my test Forth revealed – I am still miles away from a powerful product that is near to complete and which the first purchasers of the Beagle-V or whatever other RISC-V SBC makes to the mass market first.

Experience with the Raspberry Pi shows that SBCs can be popular and so interest in RISC-V based SBCs might be considerable if they come in at a competitive cost point (though that is probably some time away yet as the market will need to build).

I enjoy the effort but I am wondering if I should keep going.

A RISC-V single board computer

I finally have a RISC-V based single board computer (SBC) – the Nezha from RV Boards shipped to me directly from China.

It’s tiny (about the same form-factor as a Raspberry Pi though) and relatively expensive (it cost me just over £100 to order and get it shipped here) but whilst I was slightly concerned I was being a bit naïve in buying it (as it was either a scam or it wouldn’t work), it boots (slowly) into Linux (see image) and works (slowly).

Can RISC-V cores (which are ‘open source hardware’ and free from licensing fees) break ARM’s grip on SBCs and similar devices? A year ago the answer looked like a very clear negative as, despite years of hype, RISC-V designs just weren’t moving off the page and into silicon. Now it looks much more uncertain as the Nezha is actually the second RISC-V SBC to ship (the other, the Beagle-V, has only been distributed to a select group of developers so far – and this didn’t include me despite my application – but is expected to be available globally in the autumn).

The plans are for RISC-V SBCs retailing for less than $20 inside a year and – crucially – for the RISC-V cores to feature vector extensions which could mean some interesting use-cases being opened up.

(If you want to know more about RISC-V or if you are thinking of starting a RISC-V assembly project I cannot recommend The RISC-V Reader highly enough.)

Right now I am trying to get Riscyforth to run on my machine.

Having trouble building the riscv64-unknown-elf- toolchain?

I was – for quite a long time today, so I thought I’d share this fix. My problem was with downloading the glibc and newlib repos.

These were marked as being at git://sourceware.org/git/glibc.git and git://sourceware.org/git/newlib-cygwin.git.

When I replaced git:// with https://, the problem was solved.

First year as a software engineer

Today marks the anniversary of me starting work as a software engineer. I love the job – despite some of the real challenges I’ve faced in a radical career change – and I do feel so very lucky to have got it in an exceptionally difficult time.

Some of the changes are about how I see myself – after more than 30 years of working in communications and public policy I (regardless of what others thought about me or even whether I was right or wrong) was generally very confident in my own judgment and ideas. I’d been around the track – more than once – and whether you liked it or not I had a view I’d generally express. Now I am the start-of-career, not-long-out-of-university beginner. It can be daunting sometimes and I get things wrong, though my colleagues are generally happy to help (though everyone working remotely does sometimes make that a little harder).

Well, I’m not quite new to everything – I know how corporate things work and while I am nobody’s manager I do know what that is about too (or at least I think I do).

Secondly, I am very much working in an engineering environment and not a computer science one. The differences are subtle and I cannot quite articulate them, but they are certainly real. “Scientists” (whether computing scientists – applied mathematicians really – or hard scientists) and engineers do tend to look at each other a little warily, and before I’d always been on the “other” side of this. But I am getting used to this too.

Above all it’s great to work somewhere where every day I am expected to think and apply that thought to solve novel and interesting problems.

Coming soon: RISCYFORTH

When I was much younger FORTH fascinated me as an alternative interpreted language for the Z80 eight-bit processor machines I was typically using.

Compared to BASIC – the language that the Sinclair ZX80, ZX81 and Spectrum came with – FORTH was reputedly lightening fast and very powerful.

My brother and I even obtained a tape copy of somebody’s FORTH for the ZX80 and we ran it – and it certainly was fast. But it also lacked the simplicity of BASIC and the tape was soon handed back.

But I’m back on the case again, inspired by this (long out of print but widely available on the web) book – Threaded Interpretive Languages – and by the prospect of a single board RISC-V computer – the BeagleV – coming out this year.

Currently I am targeting the PK proxy kernel on the Spike Risc-V emulator for RISCYFORTH but if and when I get a real BeagleV I’ll immediately switch to that (I applied to be an early user but have heard nothing so while the signs are that the project itself is making good progress it looks like I’ll have to wait to get my hands on one.)

I struggled with getting the mechanics of RISCYFORTH right for a long time but in the last week I’ve finally started to make serious progress and it actually does things (only in immediate mode for now). The picture shows my very first success with a multi-token command line from a couple of evenings ago and it’s come on a fair bit since then.

It’s nowhere near a releasable state but it’s rapidly improving.

Why bother? Well I think it’s important that RISC-V succeeds as a disruptor of what is starting to look like an ARM monopoly and so contributing to the ecosystem of the first single board seriously affordable RISC-V device matters. And, of course, because it’s there.

Always yield to the hands-on imperative (from this classic).

Update: My brother actually thinks we borrowed somebody’s Jupiter Ace which was a Z80-based FORTH computer of a very similar size to a ZX81 – and I think he might be right.

Why I bought a fax machine

Actually, I didn’t realise I had bought a fax machine until the laser printer I knew I had bought turned up and I read on the packaging that it was also a fax machine.

(Fax is perhaps the most disruptive technology I’ve seen rise and fall in my time as an adult – I last used one in 2005 as far as I can recall but only 15 years earlier they were seen as cutting edge – but no matter…)

Are printers like fax machines in another way too? Destined to all but disappear as the tyranny of the screen grows ever stronger? The reasons that motivated me to buy the laser printer (and not just another cheap inkjet that produces shoddy output and falls apart after a few months) make me think not.

• Paper is much more flexible than a screen – try scribbling a note on your screen and see how that goes.
• Paper is the ‘rest energy’ form – it’s true that printing a page takes a lot more energy than clicking on a HTML link, but paper is more or less the zero energy, zero technology form of reading something – it’s generally easier to do than reading something on a screen (and if you drop a page you don’t generally risk losing you ability to read either until you buy a new set of eyes).
• Paper’s flexibility makes it easier to see links – this is a killer application for paper in my field of software engineering (though maybe not all engineers would agree) – you can see much more information at once.
• Too many screens aren’t really very good for reading – too many screens on small devices just aren’t very good for reading text. When we print something we generally print it at a size that’s optimised for reading.
• Screens tire your eyes in the way that paper just doesn’t.

Getting a laser printer as opposed to an ink jet feels like a bit of an indulgence but as every other cheaper printer we’ve had over the years has generally fallen apart quickly I am hoping it is going to deliver long-term satisfaction.

Alexa, tell me what changed your mind

We were given an Echo Dot for Christmas. And it’s just brilliant.

I have to admit I was pretty cynical – my principal experience with Apple’s voice activated “Siri” is that it doesn’t understand my accent (even though you can select an Irish voice for the output, forget about it for the input.)

But this is really great. It sits in the kitchen and has essentially replaced the digital radio and the fact that you can ask it (simple) things is a bonus.

One of the best things about it is that it allows me to spend 10 – 15 minutes listening to “Morning Ireland” on RTÉ Radio 1 every morning as I eat my toast – easy access to that perspective on world events (and on what the only country with a land border with the UK thinks about what is happening here) is a great thing to have.

Cannot recommend it highly enough.

A puzzle from Donald Knuth

Recently I had to write some code to generate a pseudorandom number in a system with very limited sources of entropy. So, of course I turned to Donald Knuth and, in particular, Volume 2 – Seminumerical Algorithms – in the magisterial The Art of Computer Programming.

Reading through the questions/exercises I then came across this one:

Prove that the middle-square method using 2n-digit numbers to the base b has the following disadvantage: if the sequence includes any number whose most significant n digits are zero, the succeeding numbers will get smaller and smaller until zero occurs repeatedly.

(Knuth rates this question as ’14’ and, using his scale of difficulty which places a ’10’ as a minute to solve and a 20 as twenty minutes, probably means this should take about 7 or 8 minutes but I’ve spent much, much longer on it than that!)

A quick explanation: the middle-square method is a naive (though actually first suggested by none other than John von Neumann) random number generation method where we take a number n-digits long, square it and take the middle n-digits as our next seed or random number.

At first I thought I’d found an example where Knuth’s proposition appears to be false.

Let and the seed number be then every subsequent number in the sequence is also 60 (obviously that’s as useless as repeated zeros for a random number generator.) But the problem with that is, that although it demonstrates a weakness in the middle square method, it doesn’t fit Knuth’s definition of the problem. What is here? If ( is the minimum for middle values), then $N_o = 0060 $ and and so (thanks to Hagen von Eitzen for clarifying this for me.)

So let’s look at the general case. (I also this explanation to Hagen von Eitzen, as compared to my very long-winded first attempt – though any errors that follow are mine not his.)

So we have a number which we think of as a digit number – though the first digits are 0. Then (as the largest can be is .)

Thus as the largest can be is then:

And

If we have a digit number then the biggest number of digits we can get from the out put is , but in our case we only have digits to worry about so the biggest size can be is digits, as again the leading digits will be 0.

So, to apply the middle square method we need to lose the lower digits – i.e., take .

From the above:

If then will always , so the sequence decreases until .

The long haul

Far too much debate in the UK about responding to SARS-CoV-2 has been about short-termist responses. So, for instance, just as every lockdown has begun to have real effect it has been lifted in the name of the economy.

The result has been we are now in the longest lock-down of all, we’ve got the deepest economic setback of any major economy (though obviously there are other things going on to cause that too) and we have one of the highest death rates in the world. Not good.

It ought to be becoming clearer to more people that, actually, even after a mass vaccination programme (the one area where the UK has, thankfully, done well), the virus will not be gone from our lives. I don’t think there will, in my lifetime, be a return to what was fully “normal” as recently as December 2019.

Over time we can expect, as a species, to see the threat from the virus diminish as, like the common cold, more children who catch it while young grow to adulthood with a fully primed immune system. For the rest of us there will be vaccines – and there will also be mutations that may threaten our vaccine-acquired immunity.

We cannot stop dangerous mutations arising – so long as the virus is in circulation it will mutate and, if a mutation improves the virus’s ability to evade vaccines, those mutations will spread.

We can, though, slow the speed of the spread of any mutation through – you guessed it – social distancing, mask wearing and test-and-trace protocols. So these may eventually be relaxed as vaccination reaches more and more people, but it is hard to see them ever going away completely. I don’t expect you are going to be let into a hospital without wearing a mask for very many years to come, for instance.

Once we come to terms with the fact that we are here for the long haul we need to start reordering our society in that light. One of the things that surely must follow is some form of immunity/vaccination passport.

Until recently I thought this was a terrible idea – but since I recognised the truly long-term nature of the threat I have come to see such passports as inevitable, and necessary, and so the key issue is how they are introduced and used.

My initial thoughts are that firstly they should be a citizen’s right – everyone should be able to get one and access shouldn’t depend on wealth.

Secondly they should be regulated to an international standard that, as far as is practical, protects privacy and avoids unnecessary state monitoring. Or to be more direct: if the Russian (or any other) state wants to insist its citizens carry the equivalent of an electronic tag with them everywhere there isn’t much we can do to stop it, but we could say such devices are not recognised for use here.

Thirdly – and related to the first point – with the obligation to have one should come the right to access services. Public bodies or other service providers might have legitimate reasons to restrict access to those who have been vaccinated or are otherwise certificated, but they should not be able to refuse access to anyone who meets the criteria either. In other words if your body or company requires access to the information the passport contains then it must also submit to the responsibilities that come with it.