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

Yasu 4.0.0 β - System maintenance app; p...
Yasu was created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks quickly within a... Read more
Skype 7.37.0.178 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
EtreCheck 3.0.5 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Amadeus Pro 2.3.1 - Multitrack sound rec...
Amadeus Pro lets you use your Mac computer for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its... Read more
NeoFinder 6.9.3 - Catalog your external...
NeoFinder (formerly CDFinder) rapidly organizes your data, either on external or internal disks, or any other volumes. It catalogs all your data, so you stay in control of your data archive or disk... Read more
WhatsApp 0.2.1880 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
Hazel 4.0.6 - Create rules for organizin...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a familiar... Read more
Apple iBooks Author 2.5 - Create and pub...
Apple iBooks Author helps you create and publish amazing Multi-Touch books for iPad. Now anyone can create stunning iBooks textbooks, cookbooks, history books, picture books, and more for iPad. All... Read more
MYStuff Pro 2.0.26 - $39.99
MYStuff Pro is the most flexible way to create detail-rich inventories for your home or small business. Add items to MYStuff by dragging and dropping existing information, uploading new images, or... Read more
MarsEdit 3.7.8 - Quick and convenient bl...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more

How to get past Vulture Island's tr...
Vulture Island is a colorful and quirky mish-mash of platforming and puzzles. It’s creative and fresh, but sometimes the game can throw a curveball at you, leaving you stuck as to how you should progress. These tips will help you explore smoothly... | Read more »
The new Clash of Kings is just for Weste...
If you’ve played the original Clash of Kings, you’ll probably recognise the city building, alliance forging and strategic battles in Clash of Kings: The West. What sets this version apart is that it’s tailor made for a Western audience and the... | Read more »
Frost - Survival card game (Games)
Frost - Survival card game 1.12.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.12.1 (iTunes) Description: *Warning: the game will work on iPhone 5C and above and iPad Pro / 4. Other devices are not supported* | Read more »
How to build and care for your team in D...
Before you hit the trail and become a dog sledding legend, there’s actually a fair bit of prep work to be done. In Dog Sled Saga, you’re not only racing, you’re also building and caring for a team of furry friends. There’s a lot to consider—... | Read more »
How to win every race in Dog Sled Saga
If I had to guess, I’d say Dog Sled Saga is the most adorable racing game on the App Store right now. It’s a dog sled racing sim full of adorable, loyal puppies. Just look at those fluffy little tails wagging. Behind that cute, pixelated facade is... | Read more »
Let the war games commence in Gunship Ba...
Buzz Lightyear famously said, “This isn’t flying, this is falling – with style!” In the case of Gunship Battle: Second War, though, this really is flying - with style! The flight simulator app from Joycity puts you in control of 20 faithfully... | Read more »
How to get a high score in Fired Up
Fired Up is Noodlecake Games’ high score chasing, firefighting adventure. You take control of a wayward firefighter who propels himself up the side of a highrise with blasts of water. Sound silly? It is. It’s also pretty difficult. You can’t... | Read more »
NBA 2K17 (Games)
NBA 2K17 1.0 Device: iOS iPhone Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Following the record-breaking launch of NBA 2K16, the NBA 2K franchise continues to stake its claim as the most authentic sports video... | Read more »
Dog Sled Saga (Games)
Dog Sled Saga 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: A game by Dan + Lisa As a rookie musher, foster a dogsledding team whose skills will grow if they're treated right. Week by... | Read more »
60 Seconds! Atomic Adventure (Games)
60 Seconds! Atomic Adventure 1.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2 (iTunes) Description: 60 Seconds! is a dark comedy atomic adventure of scavenge and survival. Collect supplies and rescue your family... | Read more »

Price Scanner via MacPrices.net

21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379 $120 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP - 21″ 1... Read more
13-inch 2.7GHz/256GB Retina MacBook Pro on sa...
Amazon.com has the 13″ 2.7GHz/256GB Retina Apple MacBook Pro on sale for $151 off MSRP including free shipping: - 13″ 2.7GHz/256GB Retina MacBook Pro (sku MF840LL/A): $1348 $151 off MSRP Read more
Apple TVs on sale for up to $50 off MSRP
Best Buy has 32GB and 64GB Apple TVs on sale for $40-$50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
Duplicate Sweeper Free On Mac App Store For O...
To celebrate the launch of Apple’s latest macOS Sierra, Stafford, United Kingdom based Wide Angle Software has announced that its duplicate file finder software, Duplicate Sweeper, is now available... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina Apple MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1174.99 $125 off MSRP - 13... Read more
Evidence Surfaces Pointing To New A10X Chip F...
Citing a job description for a Project Lead position at Apple’s Austin, Texas engineering labs, Motley Fool’s Ashraf Eassa deduces that development is progressing well on Apple’s next-generation in-... Read more
Check Print’R for macOS Allows Anyone to Easi...
Delaware-based Match Software has announced the release and immediate availability of Check Print’R 3.21, an important update to their easy-to-use check printing application for macOS. Check Print’R... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Apple refurbished 15-inch Retina MacBook Pros...
Apple has Certified Refurbished 2015 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2... Read more

Jobs Board

Sr. *Apple* Mac Engineer - Net2Source Inc....
…staffing, training and technology. We have following position open with our client. Sr. Apple Mac Engineer6+ Months CTH Start date : 19th Sept Travelling Job If Read more
*Apple* Retail - Multiple Positions-Norfolk,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 51829230 Detroit, Michigan, United States Posted: Sep. 19, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC is an Read more
US- *Apple* Store Leader Program - Apple (Un...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.