TweetFollow Us on Twitter

Forth Blocks
Volume Number:1
Issue Number:10
Column Tag:Forth Forum

"Converting Forth Blocks to Ascii Text"

"Accuracy in Modula-2 Reviewed"

By Jörg Langowski, Chemical Engineer, Fed. Rep. of Germany, MacTutor Editorial Board

With the advent of other Forth systems than MacForth, and Forth-related packages such as NEON, a utility is needed that lets us quickly convert the MacForth 'Blocks' format into a standard ASCII text file and back. NEON, for instance, expects its input from a normal text file. Also this Journal expects its input from a MacWrite file, and after I have written an example program, cutting it out of the Forth screens and pasting it into my column is quite cumbersome.

So here is a routine that does this job automatically (it contains some ideas out of a program on one Call-A.P.P.L.E. public domain disk). At the same time we are going to learn something about the Standard File Interface package, which is undocumented (but fully usable) in MacForth 1.1.

What do we need to know to convert files from Blocks to Text format and back? The type of a Blocks file is BLKS and the creator M4TH, a Text file such as saved by 'text only' MacWrite or MDS Edit is of type TEXT and creator MACA (this probably stands for Mac Ascii). In principle, both files contain ASCII text, which, however, is organized differently.

The format of a Blocks file

MacForth blocks files consist of screens , each of which contain 16 lines of 64 characters. One line is always 64 characters long and padded with blanks after the last character. This format is a relic from early FORTH times and - in my opinion - rather obsolete. But since the MacForth editor uses it, we have to live with it. The length of a file is of course very simply related to the number of screens; each screen occupies exactly 1024 bytes.

Text files, on the other hand, contain lines of ASCII characters which are separated by carriage returns (CR).

One very simple thing that one can try out to communicate between the two types of files is to change type and creator of a Blocks file to TEXT and MACA, hoping that it is recognized by Edit, for example. When I tried this, it would show a file that had only one line (of course, since there are no CRs). So we do have to read the Blocks file, line by line, and create a new text file to which we write those lines.

Reading Forth blocks

A Forth block in a file is accessed through the word BLOCK, which accepts the block number on top of stack and returns the address of a buffer that contains the block. The block is automatically read in if it is not already there.

The position of a line in the block is at (64 * line number). The word >LINE.START in the program example returns the address of a line in a given block. We then remove trailing blanks from this line, add a CR at the end and write it to the Text file (which we have opened before). This is what the word COPY.BLOCK does, which is called from the main menu: It traverses the Blocks file line by line and writes the Text file.

ASCII to Blocks conversion

The reverse direction is a little bit more complicated. The total number of lines in a blocks file is known exactly from its size, so we know ahead of time how many screens we have to convert; also a Text file can be extended arbitrarily by just adding lines. Not so the other way around: a Blocks file must be extended by appending blocks before writing to them, and the end of a Text file is known only when an end-of-file occurs.

In the example, each text line is read into the string variable TEXT.BUF with the character count in the first byte and the actual line in the following bytes. This string is then copied into a new line in the buffer; when 11 lines have been processed in this way, the buffer is written out to disk (UPDATE FLUSH) and the Blocks file extended by one block. The last five lines of each block stay blank for easier editing. Some editing is necessary because the block boundaries will often split your definitions.

Choosing input and output files - the standard file package

So the principle of this utility routine has been set up. But we still have to open the files that we want to work on. To make file access more comfortable, let's use the standard Macintosh file package to select those files.

You've seen the dialog boxes that make up the interface to this package many times. Whenever you are supposed to select a file for input, a Mac application that conforms to the User Interface standards will show you a list of files to select from and option buttons that let you change drives, eject disks or quit the operation.

When you select a file for output (or save) you are presented with an input box with a default file name:

and when the file name that you give already exists on that disk, the standard file package will ask for reconfirmation to overwrite that file.

All these functions are built into two toolbox routines, SFGetFile and SFPutFile. MacForth provides built-in interfaces to those routines, the words (GET.FILE) and (PUT.FILE). The Forth words expect less parameters than the corresponding toolbox traps.

(GET.FILE) needs, from bottom to top of stack:

- a point (2*16 bit) where the top left of the dialog box is to be located;

- the address of a prompt string (zero for no prompt);

- the address of a list of file types to be displayed;

- the number of different file types;

- the address of a reply record.

(PUT.FILE) needs:

- the top left point;

- the address of a prompt string;

- the address of a string which may contain the default file name and later contains the actual file name;

- the address of a reply record.

Information about the user's response to the dialog box is contained in the reply record. The format is:

- 2 bytes boolean, true if OK, false if Cancel button was clicked;

- 4 bytes of file type information;

- 2 bytes integer, contain the volume reference number (important if volume was changed);

- 2 bytes integer, file version number, not used here;

- 64 bytes that contain the file name in Mac string format (count byte plus characters).

The list of file types is an array of 4 byte integers; each 4-byte cell contains one valid type designator, such as PICT, TEXT, DATA, etc. On calling (GET.FILE), only those files corresponding to one of the designators will be displayed. Invisible files will be displayed, too.

In our program, input and output files are set up using the standard file interface by the words TEXT.OPEN, BLOCK.OPEN, TEXT.CREATE and BLOCK.CREATE. After the dialog has been processed, the volume reference number (which might have been changed from the default volume) is moved into the file's FCB and the type and creator fields are set depending on whether a Text or a Blocks file is written. Thereafter, the actual file conversion takes place.

During the execution of the conversion routines the activate event is switched off. If you don't do this, the main Forth window would be activated again after the first file dialog has been processed, executing an ABORT and jumping back to the 'ok' prompt, quitting your program. Try this out and see what happens when you leave out line 6 in the CHANGE.MENU definition.

With that little routine, creating MacWrite listings from your Forth programs will be easy now.

Floating point glitches in Modula-2

Even though I am responsible for Forth, I must make one more Modula comment.

Watch out when you're using math!

I have become extremely careful in this respect. The 32-bit routines are fast, true. In order to be useful, they should also give correct results (within rounding errors). This is not so. Try the example in listing 2 (WindowIO is a module of my own that just sets up a standard window for I/O). The program just keeps adding smaller and smaller numbers to 1.0, which I did originally as an accuracy test. The output is shown there, too. Sometimes the output routine seems to fail, sometimes the addition itself. And I thought this was a system I could use for some of my calculations in the lab oh well. No more comments.

Surprisingly enough, though, a non-linear curve fitting program that I wrote in Modula seems to work well, without major problems. It may be that the bug shows up only when the numbers are close to integers (???). Any comments from readers with similar experiences are appreciated, any help even more. (Richard Ohran, are you reading this? If not, a bug report will follow.)

Listing 1: Converting text to blocks files

( Forth <-> Ascii Conversion)              ( © 1985 MacTutor by J. Langowski 
)

: tx-blks ;

variable ifile#  -1 ifile# ! 
variable ofile# -1  ofile# !    
: ifile ifile# @ ;  : ofile ofile# @ ;

hex 4D414341 constant "maca decimal
create ="blks      "blks ,
create ="textdata  "text , "data ,

18 field +fcb.name    22 field +fcb.vrefnum
32 field +fcb.type    36 field +fcb.creator

( standard file reply record fields )
00 field +good    : @good  +good w@ ;
02 field +ftype   : @ftype +ftype @ ;
06 field +vrefnum : @vrefnum +vrefnum <w@ ;
10 field +fname

create ireply 80 allot    
ireply +fname constant iname
create oreply 80 allot    
oreply +fname constant oname
variable screen#        variable cur.line#
create text.buf 100 allot 
99 constant text.read.limit
5 constant ch.menu

: moverefnum  ( file#\reply -- )
    @vrefnum  swap >fcb +fcb.vrefnum w! ;

: get.input.name 
      >r >r >r
      100 100 xy>point  0   r>  r>  r@
      (get.file) page r> @good 
      0= if abort then  ;

: get.save.name
      page >r >r >r  
      100 100 xy>point  r>  r>  r@
      (put.file) r> @good 
      0= if abort then ;

: text.open  
    next.fcb ifile# ! 
    page ." Text file to convert:"
    ="textdata 2 ireply get.input.name
    iname ifile assign 
    ifile ireply moverefnum
    ifile open   ?file.error
    ifile rewind ?file.error ;

: block.open
    next.fcb ifile# ! 
    page ." Blocks file to convert:"
    ="blks 1 ireply get.input.name
    iname ifile assign 
    ifile ireply moverefnum
    ifile open  ?file.error  ifile select ;

: block.create 
   next.fcb ofile# !
   " Mac Tutor Blocks" 
   oname over c@ 1+ cmove
   " Save as:" oname oreply get.save.name
   oname ofile assign
   ofile oreply moverefnum ofile delete
   ofile create.blocks.file ?file.error
   ofile open ?file.error  ofile select
   2 ofile append.blocks  
   1 screen# !   0 cur.line# !
   0 block b/buf bl fill update flush ;

:  text.create 
   next.fcb ofile# !
   " Mac Tutor Text" oname over c@ 1+ cmove
   " Save as:" oname oreply get.save.name
   oname ofile assign    
   ofile oreply moverefnum ofile delete
   ofile create.file ?file.error
   ofile open ?file.error  ofile rewind
   ofile get.file.info
   "text ofile >fcb +fcb.type !
   "maca ofile >fcb +fcb.creator !
   ofile set.file.info  ;

: >line.start ( block\line -- addr of line)
  64 * swap block + ;

: write.line 
    >line.start 64 -trailing
    over over + 13 swap c!  ( add CR )
    1+  ofile write.text  ;

: write.screen
    dup 16 0 do dup i ( screen\line )
    over over . 2 spaces . cr ( debug )
    write.line  loop drop ( n ) ;

: copy.block  ifile get.eof b/buf /
    0 do  i . cr i write.screen
      do.events drop loop ;

: read.line  ifile current.position
   text.buf 1+  text.read.limit  
   ifile  read.text
   ifile current.position swap -  
   text.buf  c!  ;

: copy.line 
  read.line  ?eof not
  if cur.line# @ dup .
     64 * screen# @ dup . cr 
     block +  text.buf 1+  swap
     text.buf c@ 1- cmove  
     1 cur.line# +!  cur.line# @ 10 >
     if 0 cur.line# !   update flush
        1 screen# +!  1 ofile append.blocks
     then  do.events drop true
  else update flush false then ;

: copy.text  begin copy.line not until ;

: >text block.open text.create copy.block ;

: >block text.open block.create copy.text ;

: change.menu
    0 " Change" ch.menu new.menu
    " Forth->Ascii;Ascii->Forth;"  
    ch.menu append.items draw.menu.bar
    ch.menu menu.selection:
    1 activate.event scale -1 xor events !
    0 hilite.menu
     case  1 of  >text      endof
           2 OF  >block     endof endcase
    events on do.events abort ;

change.menu

Listing 2: Modula 2 FP 'accuracy test'

MODULE Accuracy;

FROM InOut IMPORT ReadCard, WriteCard, 
        WriteString, WriteLn, ClearScreen;
FROM RealInOut IMPORT ReadReal, GWriteReal;
FROM WindowIO IMPORT SetupWindow;
FROM EventManager IMPORT Button;
VAR  a,b : REAL;  
 
BEGIN
SetupWindow
("Accuracy test",40,40,350,450,4,9);
a := 1.0; b := 1.0;
WriteString 
("        a           b           a+b"); WriteLn;

REPEAT 
  b := b/10.0;
  GWriteReal(a,12); GWriteReal(b,12);
  GWriteReal(a+b,12); WriteLn;
  WHILE Button() DO END;
UNTIL (b = 0.0);

REPEAT UNTIL Button();

END Accuracy.

Listing 3: Output of the Accuracy program

(terminated before underflow occurred). Note that b is sometimes printed as zero, although a+b seems to be correct; and for some smaller values of b (1.0E-19 to 1.0E-25) a+b starts to behave very strange.

        a          b          a+b
    1.000000   0.1000000      1.100000
    1.000000   0.01000000     1.010000
    1.000000   0.00000000     1.001000
    1.000000   0.00010000     1.000100
    1.000000   0.00001000     1.000010
    1.000000   0.00000100     1.000001
    1.000000   0.00000010     1.000000
    1.000000   1.0000E-08     1.000000
    1.000000   1.0000E-09     1.000000
    1.000000   1.0000E-10     1.000000
    1.000000   1.0000E-11     1.000000
    1.000000   0.0000E-13     1.000000  ?
    1.000000   1.0000E-13     1.000000
    1.000000   1.0000E-14     1.000000
    1.000000   1.0000E-15     1.000000
    1.000000   1.0000E-16     1.000000
    1.000000   1.0000E-17     1.000000
    1.000000   0.0000E-19     1.000000  ?
    1.000000   1.0000E-19     2.844674  ???
    1.000000   1.0000E-20     1.184467  ??
    1.000000   1.0000E-21     1.018447  ??
    1.000000   0.0000E-23     1.001845  ??
    1.000000   1.0000E-23     1.000184  ?
    1.000000   1.0000E-24     1.000018  ?
    1.000000   1.0000E-25     1.000002  ?
    1.000000   0.0000E-27     1.000000  ?
    1.000000   1.0000E-27     1.000000
    1.000000   1.0000E-28     1.000000
    1.000000   1.0000E-29     1.000000
    1.000000   1.0000E-30     1.000000
    1.000000   1.0000E-31     1.000000
    1.000000   1.0000E-32     1.000000
    1.000000   1.0000E-33     1.000000
    1.000000   1.0000E-34     1.000000
    1.000000   1.0000E-35     1.000000
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Live Home 3D Pro 3.6.2 - $49.99
Live Home 3D Pro is powerful yet intuitive home design software that lets you build the house of your dreams right on your Mac, iPhone or iPad. It has every feature of Live Home 3D, plus some... Read more
RapidWeaver 8.2 - Create template-based...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Opera 60.0.3255.109 - High-performance W...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
DEVONthink Pro 3.0beta2 - Knowledge base...
DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research papers, your life often fills your hard drive in the... Read more
Tunnelblick 3.7.9 - GUI for OpenVPN.
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
Carbon Copy Cloner 5.1.9 - Easy-to-use b...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
Dropbox 73.4.118 - Cloud backup and sync...
Dropbox is an application that creates a special Finder folder that automatically syncs online and between your computers. It allows you to both backup files and keeps them up-to-date between systems... Read more
Postbox 6.1.18 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
Wireshark 3.0.2 - Network protocol analy...
Wireshark is one of the world's foremost network protocol analyzers, and is the standard in many parts of the industry. It is the continuation of a project that started in 1998. Hundreds of... Read more
BetterTouchTool 2.856 - Customize multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more

AFK Arena guide - Everything you need to...
Ok, so if you're like me, you've been playing (and sometimes waiting) your way through AFK Arena, only to learn there's a lot more to it than there appears on the surface. There's guilds, a PvP arena, and all sorts of other systems and game modes... | Read more »
Explore an epic fantasy world in MMORPG...
Webzen have just announced the official launch date for its stunning MMORPG ‘MU Origin 2’ which will arrive for iOS and Android on May 28th. It will be the second spinoff from the classic PC-based MU Online, and it looks to further refine the... | Read more »
Solar Explorer: New Dawn guide - Tips an...
Solar Explorer: New Dawn is a lunar lander game that really ratchets the intensity up to 11. With all of the asteroids flying around as you fly around at seemingly breakneck speeds, it can be easy to feel overwhelmed bythe whole thing. | Read more »
The Dalaran Heist - How Hearthstone...
I am someone who wrote Hearthstone off a while ago. It was hard not to try and stick with it. The game has incredible production values and a core of really great talent working on the game continuously to keep it feeling fresh and fun (full... | Read more »
Steam Link App - Everything You Need to...
Steam Link has finally released for iOS! That’s right, you can play your epic backlog of PC games on the go now. Well… sort of. While the Steam Link app was announced seemingly ages ago, it only got actual approval for release last night. Check out... | Read more »
Pre-register now for endless superhero r...
Talking Tom Hero Dash is set to take the ever-popular Talking Tom and Friends franchise in a brand new direction as it opens pre-registration to players worldwide. Not only does it promise to be a beautifully rendered, fast-paced, action-packed... | Read more »
AFK Arena - Guild Wars guide
Ok, so if you're like me, you've been playing (and sometimes waiting) your way through AFK Arena, only to learn there's a lot more to it than there appears on the surface. There's guilds, a PvP arena, and all sorts of other systems and game modes... | Read more »
Superhero-themed Talking Tom Hero Dash i...
One of the exciting releases that we’re looking forward to is Talking Tom Hero Dash, an upcoming superhero-themed runner created by Outfit7. This new game is an action-packed endless runner that takes you on an epic adventure to assemble the... | Read more »
Kingdom Rush Vengeance Update Guide 2 -...
Kingdom Rush: Vengeance just got updated once again to add more content to the game. This addition, called The Frozen Nightmare, adds three new levels, five new enemies, two new heroes, and some new achievements. | Read more »
Save the world with SCIENCE in the upcom...
Previous versions of space colonization game TerraGenesis encouraged you to explore the galaxy and settle its planets. The eagerly-awaited 5.0 update will try to smash them to bits. Yep, with a new "world killers" setting, you can unleash... | Read more »

Price Scanner via MacPrices.net

12″ 1.2GHz MacBooks on sale for $999, $300 of...
Amazon has current-generation 12″ 1.2GHz Retina MacBooks on sale for $300 off Apple’s MSRP. Shipping is free: 12″ 1.2GHz Space Gray MacBook: $999.99 $300 off MSRP 12″ 1.2GHz Silver MacBook: $999.99 $... Read more
Here’s how to save $200 on Apple’s new 8-Core...
Apple has released details of their Education discount associated with the new 2019 15″ 6-Core and 8-Core MacBook Pros. Take $200 off the price of the new 8-Core model (now $2599) and $150 off the 15... Read more
Price drops! 2018 15″ 2.2GHz 6-Core MacBook P...
Amazon has dropped prices on clearance 2018 15″ 2.2GHz 6-Core Touch Bar MacBook Pros by $300 with models now available for $2099. These are the same models sold by Apple in their retail and online... Read more
Apple drops prices on 2018 13″ 2.3GHz Quad-Co...
Apple has dropped prices on Certified Refurbished 2018 13″ 2.3GHz 4-Core Touch Bar MacBook Pros with prices now starting at $1489. Apple’s one-year warranty is included, shipping is free, and each... Read more
Apple drops prices on 2018 Certified Refurbis...
Apple has dropped prices on clearance 2018 15″ 6-Core Touch Bar MacBook Pro, Certified Refurbished, with models available starting at only $1999. Each model features a new outer case, shipping is... Read more
Price drops! Clearance 2018 13″ Quad Core Mac...
Amazon has dropped prices on 2018 13″ Apple Quad-Core MacBook Pros with models now available for $250 off original MSRP. Shipping is free. Select Amazon as the seller, rather than a third-party, to... Read more
How Much Is ‘Solace’ Of Mind Worth When Buyin...
COMMENTARY: 05.22.19- Smartphone cases give us peace of mind by providing ample protection for such a fragile gadget and the sky’s the limit as far as choices go with a plethora of brands, styles,... Read more
Get a 13″ Touch Bar MacBook Pro for the lowes...
Apple has Certified Refurbished 2017 13″ 3.1GHz Dual-Core i5 Touch Bar MacBook Pros available starting at $1439, ranging up to $390 off original MSRP. Each MacBook features a new outer case, shipping... Read more
Apple adds new 15″ 8-Core MacBook Pro to line...
Apple has added a new 15″ MacBook Pro to its lineup featuring a 9th generation 2.3GHz 8-Core Intel i9 processor, 16GB of RAM, a 512GB SSD, and a Radeon Pro 560X with 4GB of GDDR5 memory for $2799.... Read more
21″ 2.3GHz iMac available for $999 at B&H...
B&H Photo has the 2018 21″ 2.3GHz Apple iMac on sale for $100 off MSRP. This is the same model offering by Apple in their retail and online stores. Shipping is free: – 21″ 2.3GHz iMac (MMQA2LL/A... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**690427BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Location Number:** 000860-Charlottesville-Store **Job Description:** **What Read more
*Apple* Mobile Master - Best Buy (United Sta...
**696430BR** **Job Title:** Apple Mobile Master **Job Category:** Store Associates **Location Number:** 001012-Bismarck-Store **Job Description:** **What does a Best Read more
Manager - *Apple* Team - SHI International...
…opportunity available in the Hardware & Advanced Solutions Department as the Manager of the Apple Team The Manager must be familiar with all aspects of Apple Read more
Best Buy *Apple* Computing Master - Best Bu...
**696375BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Location Number:** 000203-North Austin-Store **Job Description:** **What does a Read more
Geek Squad *Apple* Master Consultation Agen...
**696286BR** **Job Title:** Geek Squad Apple Master Consultation Agent **Job Category:** Services/Installation/Repair **Location Number:** 000172-Rivergate-Store Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.