View source for RBJ (Redcode oBJect)

{{FormatInfo
| extensions             = {{ext|rbj}}
| released               = 1992
| image                  = cw.png
| caption                = XRK core display
| endianness             = Little_endian
| developed by           = Marco Pontello
| reference impl         = http://mark0.net/soft-xrk-e.html
| error resiliance       = checksum          
| subcat                 = Game data files
}}

'''RBJ''' format belongs to [[XRK - Extra Redcode Kit]], a complete [[Core Wars]] system for [[DOS]]. RBJ files contains an assembled binary version of a [[Redcode]] Warrior, usually written by the [[XRA - Extra Redcode Assembler]].
RBJ files also contains info about the warrior's author, name and version of the assembler used, date & time.

== File structure overview ==

An RBJ file is composed of 3 sections: Header, Code, Tail

The Tail is represented by 1 byte used as a checksum.
To verify the integrity of a RBJ file, simply compare this value to the
calculated checksum of the first (filesize - 1) bytes (that is Header +
Code).

== Structure Descriptions ==

=== Header ===

The Header is 75 bytes long, and is composed as follow:

<pre>
Pos  Field           Len Data
---------------------------------
  0  Version ID        1 Byte - decimal
  1  Author           30 Chars
 31  Made with        30 Chars
 61  Serial Date&Time  8 FP64
 69  Split Flag        1 Byte
 70  Reserved          1 Byte
 71  Program Len       2 Int
 73  Start             2 Int
</pre>

=== Code ===

The Code block is a sequence of (Program Len) blocks as follow:

<pre>
     Field           Len Data
---------------------------------
  0  Command           1 Byte
 +1  Mode A / B        1 Byte
 +2  Operand A         2 Int
 +4  Operand B         2 Int
</pre>

=== Tail ===

One Byte as a checksum:

<pre>
     Field           Len Data
---------------------------------
  0  CheckByte         1 Byte
---------------------------------
</pre>

== Fields Descriptions ==

=== Header ===


==== Version ID ====
Decimal (Major ver. * 10 + Minor ver.)
Ex: 12 = v1.2

==== Author ====
Warrior's programmer Name/Nick

==== Made with ====
Assembler used

==== Serial Date&Time ====
Floating Point value: Dec * 86400 = seconds from midnight / Int = days from some date

==== Split Flag ====
0 = No SPL opcode used (program doesn't split)
!0 = Program may use SPL

==== Reserved ====
Not used

==== Program Len ====
Instructions count, length of the code block

==== Start ====

Point to the instruction where execution start


=== Code ===

==== Command ====

<pre>
   0 DAT
   1 MOV
   2 ADD
   3 SUB
   4 JMP
   5 JMZ
   6 JMN
   7 DJN
   8 CMP
   9 (not used)
  10 SPL
</pre>

==== Mode A / B ====

<pre>
  Field A = low nibble
  Field B = high nibble

  0 "#" Immediate
  1 "$" Direct
  2 "@" Indirect
  3 "<" Indirect autodecremented
</pre>

==== Operand A & B ====

<pre>
  2 bytes signed integer
</pre>

=== Tail ===

==== CheckByte ====
Here's how to calc the checksum byte (in [[BASIC]]-like [[pseudocode]]):
<pre>
  Sum = 0
  FOR i = 1 TO BufferLen STEP 1
    Sum = Sum + BufferByte(i)
  NEXT i
  FOR i = 1 TO BufferLen STEP 2
    Sum = Sum + BufferByte(i)
  NEXT i
  FOR i = 1 TO BufferLen STEP 3
    Sum = Sum + BufferByte(i)
  NEXT i
  FOR i = 1 TO BufferLen STEP 4
    Sum = Sum + BufferByte(i)
  NEXT i
  Sum = Sum AND 255
</pre>
== External links ==
* [http://mark0.net/soft-xrk-e.html XRK - Extra Redcode Kit]
* [http://en.wikipedia.org/wiki/Core_War Wikipedia: Core War]