Try fo fit move_t in 16 bits ? #12

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bruno · 2024-04-28T16:51:19+02:00

bruno commented

2024-04-28 16:51:19 +02:00

ideas:

Remove useless grabbed piece (saved in move_do())
shrink flags: As they are mutually exclusive: castling, e.p., promotion.

We would be left with:

from/to: 12 bits (6 bits each)
Promoted piece: 2 bits: N=0, B=1, R=2, Q=3). Promoted piece would be KNIGHT + promoted_piece
Flags: 2 bits (quiet, e.p., castle, capture or promotion). This looks short.

ideas: - Remove useless grabbed piece (saved in `move_do()`) - shrink flags: As they are mutually exclusive: castling, e.p., promotion. We would be left with: - from/to: 12 bits (6 bits each) - Promoted piece: 2 bits: N=0, B=1, R=2, Q=3). Promoted piece would be `KNIGHT + promoted_piece` - Flags: 2 bits (quiet, e.p., castle, capture or promotion). This looks short.

bruno added the

enhancement

label 2024-04-28 16:51:19 +02:00

bruno commented

2024-06-25 11:07:46 +02:00

e.p. flag can be removed: (piece == PAWN && to == ep) will do the trick
castling flag can be removed: we can test if to == from+2 or to == from - 2

- e.p. flag can be removed: `(piece == PAWN && to == ep)` will do the trick - castling flag can be removed: we can test if `to == from+2` or `to == from - 2`

bruno closed this issue

2024-06-25 11:07:46 +02:00

bruno reopened this issue

2024-06-25 11:09:32 +02:00

bruno commented

2024-06-25 11:12:06 +02:00

flags capture, double push, and promotion removed in ec2d229.
Left to do:

Use 2 bits for promoted piece
remove e.p. flag
use one (or zero) flags value for castling

flags capture, double push, and promotion removed in ec2d229. Left to do: - Use 2 bits for promoted piece - remove e.p. flag - use one (or zero) flags value for castling

bruno commented

2024-06-25 15:52:18 +02:00

Done in ffd5d05 :

move flags are now values (1, 2, 3...) instead of bitmask (1, 2, 4...)
unique value for castling flag

2 bits left to save to fit into 2 octets (16-bits).

Done in ffd5d05 : - move flags are now values (1, 2, 3...) instead of bitmask (1, 2, 4...) - unique value for castling flag 2 bits left to save to fit into 2 octets (16-bits).

bruno commented

2024-06-30 11:32:02 +02:00

Since ffd5d05, flags are values (not bitmasks) meaning that we currently have one unused value in flags (the value 3, using 2 bits). We can use this value to flag promotion.

Other ideas "save bits" :

If promoted piece uses only 2 bits, we can :
- test that piece is a pawn AND that destination square is on 1st or 8th rank
En-passant flag can be removed if we test that piece is pawn and dest square is en-passant square.
Castling flag can be removed with some changes in move_do, one of :
- test if piece is king AND distance is 2
- test is piece is king and move_fromto() is E1C1/E1G1 / E8C8/E8G8
If we know the moving piece type, we can use the same flag value for different pieces (e.g en-passant and castling)

Since ffd5d05, flags are values (not bitmasks) meaning that we currently have one unused value in flags (the value 3, using 2 bits). We can use this value to flag promotion. Other ideas "save bits" : - If promoted piece uses only 2 bits, we can : - test that piece is a pawn AND that destination square is on 1st or 8th rank - En-passant flag can be removed if we test that piece is pawn and dest square is en-passant square. - Castling flag can be removed with some changes in move_do, one of : - test if piece is king AND distance is 2 - test is piece is king and move_fromto() is E1C1/E1G1 / E8C8/E8G8 - If we know the moving piece type, we can use the same flag value for different pieces (e.g en-passant and castling)

bruno commented

2024-07-01 14:10:47 +02:00

Finished with a2451d79db

Finished with a2451d79db

bruno closed this issue

2024-07-01 14:10:47 +02:00

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Reference: bruno/brchess#12