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===== Template - A new Idea =====

So - you want to describe a new idea? Great.

We give some guidelines how to do it. Below we describe the idea of a **DUMP** utility with parts that we find useful. This text is written in [[wiki:syntax|Wiki syntax]]. You are invited to make experiments in the [[playground:playground|playground]].

Just edit this text and adapt it to your idea. If in doubt you can always save a draft and come back later.

Thanks for your contribution, 

The Project Forth Works Team

----

===== DUMP memory algorithm: display content of main memory =====

==== STATE idea ====

Forth has two states: interpreting and compiling, depending on the content of the variable STATE .
There are surprisingly many problems with this simple concept. These are caused by the fact that we may want to do  interpretation during compilation, or may desire to start new definitions (i.e. use compile state) when we have not finished compiling the current definition yet. Compounding the problem is that changing the value of STATE all the time is cumbersome, and therefore most Forth have so-called IMMEDIATE words that 


==== DUMP Implementation ====

One way to implement DUMP is to iterate in a loop line by line through memory. Say you want to display 16 bytes in each line, then this loop will start
at the start address and increment the address by 16 in each loop iteration. (If you want a different number of bytes in each line, adjust accordingly).

When you display memory in a single line you first output the current address and then have two loops that run one after the other iterating both from 0 to 15.
The first loop outputs bytes with two hexadecimal digits (or in decimal, or whatever you intend) and the second loop outputs the individual bytes as ASCII characters.

As some characters might control the output in a special way (so called control character such as 07 bell, 0A linefeed, 0C formfeed) it is wise to just output a period 
instead of the actual character, in order to get a well formatted display.


==== Pseudo code for the DUMP implementation ====

//What [[en:pfw:pseudocode|Pseudo code]] is.//

<code>
Function: dump-line ( address -- )
  output address (possibly right aligned)
  output ":" and some space
  
  LOOP i from 0 to 15:
     output byte in memory at (address+i) as two hexadecimal digits (or in another radix if desired)
     output some space
  
  LOOP i from 0 to 15:
     output byte in memory at (address+i) as an ASCII character, "." if that character is a control character (byte<32)
     
Function: dump ( address length -- )
   WHILE length is positive:
        dump-line at address
        increase address by 16
        decrease length by 16
</code>

==== Minimal Forth implementation of DUMP: ====


You can find a [[https://github.com/Project-Forth-Works/Project-Forth-Works.github.io/blob/main/minimalforth.md|Minimal Forth]] implementation of DUMP in [[en:pfw:dump-minimal_forth.fs|dump-Minimal_Forth.fs]].

You can use it as follows:

<code forth>
  ok
Create x 100 allot  ok
x 100 dump
03D694: 05 61 6C 6C 6F 74 08 00 DF 14 00 00 C1 00 08 00   .allot..?...?...
03D6A4: 1F 18 00 00 C1 00 08 00 6F 10 00 00 C1 00 08 00   ....?...o...?...
03D6B4: 4F 10 00 00 C2 00 08 00 1F 13 00 00 C2 00 08 00   O...?.......?...
03D6C4: 8F 30 00 00 C2 00 08 00 DF 14 00 00 C2 00 08 00   ?0..?...?...?...
03D6D4: 1F 18 00 00 C2 00 08 00 6F 10 00 00 C2 00 08 00   ....?...o...?...
03D6E4: 4F 10 00 00 C3 00 08 00 8F 30 00 00 C3 00 08 00   O...?...?0..?...
03D6F4: 5F 13 00 00                                       _... ok
</code>

As the original Minimal Forth has no output facility other than ''emit'' and ''.s'' (specifically no number formatting and no ''.'' or ''.r'')
this implementation seems to be over complicated.

We extended Minimal Forth to [[https://github.com/Project-Forth-Works/Project-Forth-Works.github.io/blob/main/minimalforth.md|GenericForth]] to get a
more useful small Forth.

A DUMP utility in **GenericForth** can be found in [[en:pfw:dump-genericforth.f|dump-GenericForth.f]]
This example is factored using the pseudo code description. The character output has been factored into the useful word PEMIT ( char -- ) too.


==== Various DUMP Implementations ====

Other DUMP implementations can be found at the end of this description.

Your system might lack right justified number output or even BASE for printing numbers in other radix systems. The sample implementation in [[pfw:twomoredumps.f|twomoredumps.f]] show how to circumvent this.


==== Background information ====

More about the DUMP utility can found at the [[https://en.wikipedia.org/wiki/Hex_dump|Wikipedia page for hexdump]]

Some Forth DUMP implementations display a fixed amount of bytes and leave the updated address on the stack so that
you can invoke DUMP repeatedly to display successive regions of memory.

==== Possible pitfalls with DUMP ====

Some systems have hardware memory protection that is triggered if you access memory outside the reserved area.
The dump utility can do so by trying to show this forbidden memory. Triggered memory protect might stop the current process and
terminate your session. If necessary a suitable test for the validity of used addresses might be reasonable on such systems so that
dump can issue a normal error message (or display dummy data) in theses cases and leave the system / session otherwise intact.

==== Contributions ====

<html><h2 style="background-color:yellow">Alternative Implementations</h2></html>

You have another approach to DUMP?

Please add it at the end of this document.

~~DISCUSSION~~