MANUAL FOR WRAP (6502 ASSEMBLER)

This file describes the program WRAP which demostrates how to wordwrap a block
of text in memory onto the screen.
The manual and software is (C)1998 SPROW

INSTRUCTIONS-
At the BASIC prompt,type CHAIN"WRAP"

The program will assemble itself in RAM,and then go to look for the file
called 'Tester' on the current filing system.This it will load into RAM too.

The demostration text will then be printed on the screen,wordwrapped to 40
columns (even thought the test text is not).Printing stops when a character
zero is found in the text.

Please note that this software is not intended to be a stand alone product,but
is simply a demonstration of how YOUR programs could wordwrap far faster than
the equivalent BASIC program.

HOW IT WORKS
Say we have a block of text which was written in 80 column mode,but we want to
show this is 40 column mode instead.A crude way to do this would be simply to 
print it out unmodified,but this would result in some words being broken 
across the ends of lines.

It is therefore desireable to wordwrap the text.This may be done by considering
some special cases:

Here are the 40 columns 0123456789012345678901234567890123456789
Here's a random string  ABCDE EFGHIJK LMNOPQ . RTSUVWXYZ,abcdef 
                        ghij.

Fortunately this will look OK even if we'd simply printed it out.To word wrap
you move a pointer to the 40th character,then back up 1 character at a time
until you find a space.Here,that occurs on the very first letter,as there's a
space at the end of the line.

Here are the 40 columns 0123456789012345678901234567890123456789
Here's a random string  ABCDE EFGHIJK LMNOPQ . RTSUVWXYZ,abcdefg 
                        hij.

Applying the above rules the wordwrap will be made after the full stop as that
is where the first space is.It would appear as:

Here are the 40 columns 0123456789012345678901234567890123456789
Here's a random string  ABCDE EFGHIJK LMNOPQ . 
                        RTSUVWXYZ,abcdefghij.

Which isn't very satisfactory.If instead we look for any charcter with an ASCii
value LESS THAN the letter '0' (number 48) then the wordwrap will occur at the
comma instead,as this has ASCii value 44.It'll look like

Here are the 40 columns 0123456789012345678901234567890123456789
Here's a random string  ABCDE EFGHIJK LMNOPQ . RTSUVWXYZ,
                        abcdefghij.

Much better.But what happens in the extreme cases? A 42 letter long word,or a 
zero length word.Well,when tracking backwards in search of a character less
than ASCii 48 if you realise that you're at the beginning of the string,at 
offset 0,then simply print out a fixed 40 letters.This will leave you part way 
through a string,whereupon you can then jump forward another 40 letters and
carry on as before.In this way an 85 letter string would be split up into 2 
fixed length 40 characters then a 'normal' string.

By a zero length word I mean one with a carriage return only in it.These can
be dealt with by performing a newline,then starting scanning again after the 
CR character.

KNOWN PROBLEMS/FUTURE ENHANCEMENTS-
No known problems

HISTORY-
V1.00 First version,to be added to the OS_PrettyPrint ROM for the BBC Micro

DISTRIBUTION-
The assembler which does the wordwrapping function is (C)1998 SPROW and
must not be altered without the author's permission.You are however free
to distribute any software which includes the routine,with no royalty 
payments,provided the above condition is met.