On Saturday, September 29, 2012 3:45:38 PM UTC-5, Steve Nickolas wrote:
http://1.buric.co/lrrbcd.zip
Given a sector containing a level from Lode Runner, these tools will
convert between the 256-byte (only 224 used) raw sector form and a
196-byte format made through what I call "reverse binary-coded decimal
packing".
Basically, each nibble contains a value from 0-9 (where they could take a
value up to 15). This means each byte has only 100 options, instead of
256. A range of 100 will fit in 7 bits (which have a range of 128).
Therefore by taking the converted values, and packing 8 bytes in 7 by
discarding the top bits, the file is reduced from 224 used bytes to 196.
lrrbcd.c is a tool to encode levels using this scheme.
lrunrbcd.c is a tool to decode levels using this scheme.
I haven't translated the UNRBCD algo to 6502 yet. Also, it breaks in
Watcom C, so you'll probably need to use GNU C (e.g., MinGW).
-uso.
The code in Lrrbcd.c has the following instruction that seems out of place:
tbuf[k]=((k&0xF0)>>4)*10+(k&0x0F);
Tommy