Subject: Re: EBS tournament 14th Feb
From: scc@rlgvax.Reston.ICL.COM (Stephen Carlson)
Organization: International Computers Limited, Reston, Virginia, USA
Date: 5 Feb 92 23:45:13 GMT
Message-ID: <1992Feb5.234513.22165@rlgvax.Reston.ICL.COM>

In article <1992Jan31.133553.6353@dcs.glasgow.ac.uk> fraserc@dcs.glasgow.ac.uk (Campbell Fraser) writes:
>e.g. XTC is a very effective program and will probably do very resectably if
>entered and the tournament is a round robin. However there will certainly be
>a number of programs capable of beating it which could put it out after the
>second round if XTC is drawn against them.

I have a program that was specifically designed to beat xtc.  In fact, it
even made it on the Hill for about ten rounds.  The program is called B2,
named after the stealth bomber:

;redcode verbose
;name B2
;author S.C. Carlson
;strategy Low-profile bomber
b2      add #45,ptr
        jmp 3
        dat #0
        dat #0
        mov sbomb,@ptr
        jmp 3
sbomb   dat #0
        dat #0
        mov dbomb,<ptr
        jmp b2
dbomb   dat #0
        dat #0
ptr     dat #2


Every fourth instruction of this program has a non-zero B-field.  This means
that from the get-go, xtc has only a 25% chance of even detecting it.
Furthermore, only two out of every four addresses are executed, so pattern
bombers modulo 4, like dwarf, have only a 50% chance of hitting it from the
initial position.  Also, its eventual bombing pattern is very thorough: in
the end 50% of all locations are bombed.

The disadvantages are primarily slowness and impotency against mice-like
programs.  The "jmp 3" instructions slow down the program making it about
half of the speed of dwarf and other single threaded bombers.  An updated
version (with the "sbomb spl 0" instruction at line 7) can sometimes beat
mice (with a maximum process limit of 64), the added advantage of a being a
split bomber for this program is marginal.  The updated version did not make
on the Hill.  I think this is because the Hill evolved away from bombers.

--Steve
-- 
Stephen Carlson           | ICL OFFICEPOWER Center    | In theory, theory and
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