Bit stuff

Board

The board is encoded as 64 4-bits tiles (32 bytes), and 2 bytes of header info.

Header

Attribute	Bits
white to move	1
white O-O	1
white O-O-O	1
black O-O	1
black O-O-O	1
can en passant	1
en passant column	3
counter (50-moves rule)	7

The counter needs to count up to 100 because it counts half-moves

Tiles

Attribute	Bits
color	1
piece type	3

Moves

Each move can be encoded with 2 bytes.

Attribute	Bits
from position index	6
to position index	6
is capture	1
is check	1
is mate	1
empty	1

The from position index field is important for differentiating duplicate moves (i.e. 2 rooks on the same file).

3-fold repetition

To implement this rule, we need to keep track of every position (without header) since the last capture or pawn move, so at most 100 * 32 = 320 bytes.

Sprites

Since we only use simple 1-color sprites we just need some 0's and 1's to represent our sprites (might change tho). Since the number of pixels in a sprite might not be a clean multiple of 8, we keep as a header the number of unused bits (up to 7, so we only need 3 bits) that get inserted right before the useful data, but use a full byte for convenience, tho we will probably

Attribute	Bits
# of filler bits	3
empty (header)	5
filler bits	7<=
pixel data	undef