[rc5] v3

Christopher Hodson (Consultant) cmh at fpk.hp.com
Mon Oct 27 17:08:01 EST 1997


Joseph Fisk wrote:
> 
> On Mon, 27 Oct 1997, Bill Plein wrote:
> 
> > Describing a board configuration and the move therein would take a lot more
> > data than describing a single RC-128 key, and describing all possible board
> > configurations and all possible moves for that board. Whoa, that's a HUGRE
> > library.
> 
> I think he was referring to the total possible combinations of board
> configurations.
> 
> RC5/128 has a tad more than
> 34,028,236,691,000,000,000,000,000,000,000,000,000 total
> possible keys.
> 
> I have no idea how many possible combinations there are in chess... :-P
> 

64 squares * (7 possible pieces(NULL,K,Q,B,Kn,R,p) * (2 colors))	= 64*8
bits
+ 2 * 8 bits for each pawn en passant(?) possibilities		= 16 bits
+ castle left (T/F)						= 1 bit
+ castle right(T/F)						= 1 bit
+ whose turn is it?						= 1 bit
----------------------------------------------------------------------------------
Total								= 531 bits

N.B. Many, many, many of the board combinations are either not valid,
impossible to achieve, of equivalent to other positions.  OTOH, there
should also be a field for "last x moves"

2^531 =
7029552803973744348141466418259346654483901747346744739219930582205996\
2197991997973735010720373294642967514228648763986300129157117098432640\
75804970101818523648

--
Christopher M. Hodson
System Admin (Consultant)
Hewlett Packard Engineering Services Group
cmh at fpk.hp.com
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