File format of .85G files
=========================
Compiled by David Brodbeck (gull@cyberspace.com)
Corrections by Magnus Hagander (mha@algonet.se)
Type codes compiled by Per Finander (pfimdt93@hvdc.hv.se)


The .85G files are groups of TI-85 variables.
They are also the general part of all .85x files (see README.TXT for
further information about this).
An 85G file can contain any number of variables, as long as their total
size does not exceed 64Kb.

The format of the .85G file is
------------------------------

Header     - 37h bytes
Entry1
Entry2
  ..
EntryX
Checksum   - 2 bytes


The header has the following format
-----------------------------------

Offset    Length    Comments
======    ======    ========
00h       08h       Signature. Must be "**TI85**"
08h       03h       End-Of-File marker and further signature, must be
                    1Ah 0Ch 00h
0Bh       2Ah       Comment. This is a space- or null-padded string.
                    It may _NOT_ contain any of the special characters
                    on the TI-85. All normal characters are allowed,
                    though.
35h       02h       Word: Number of bytes from [next byte to EOF]-2.
                    This variable is used to calculate the checksum
                    of the file. Read this word. Then calculate the
                    checksum on the n words that follows, where n is
                    the value you just read. After that, append the
                    checksum.


Each entry has the following format
-----------------------------------

Offset    Length    Comments
======    ======    ========
+00h      02h       Word: Bytes from next byte to end of name
                    This can be used for "fast-skipping" of the
                    variable when seeking through the file. The
                    word pointed to by this value is the size of
                    the variable, and therefor the whole thing
                    can be skipped faster.
+02h      02h       Word: Data length
+04h      01h       Byte: Type code (see table below)
+05h      01h       Byte: Name length
+06h       *h       Name (plain data, no terminating null or padding
                    spaces)
*+00h     02h       Word: Data length
*+02h     xxx       Data



The typecodes available are:
----------------------------
00    Real
01    Cplx
02    Vectr  03  Vectr complex
04    List   05  List  complex
06    Matrx  07  Matrx complex
08    Const  09  Const complex
0A    Equ
0B    Range
0C    Strng
0D-10 GDB
11    Pict
12    Prgm
13    Range
14    ?
15-1B Range


The checksum is calculated the following way
--------------------------------------------
Sum up all the words between 37h and (filesize-2), and the
value with FFFFh, and there you are. A little Pascal code
snippet to show the basic idea (programmers in other languages
should probably understand it too):

var checksum:Word;f:file;i:Integer;b:Byte;
begin
   seek(f,$37);
   checksum:=0;
   for i:=1 to filepos(f)-$39 do begin
      blockread(f,b,1);
      checksum:=checksum+b;
   end;
   blockwrite(f,checksum,2);
end;

You could also read the word at address 35h to determine how
much to compute the checksum on, if you don't want to use
the files size.