Article 1373 of rec.games.corewar:
Newsgroups: rec.games.corewar
From: pk6811s@acad.drake.edu
Subject: Re: Decrement Protection
Message-ID: <1992Oct8.141307.1@acad.drake.edu>
Lines: 46
Sender: news@dunix.drake.edu (USENET News System)
Nntp-Posting-Host: acad.drake.edu
Organization: Drake University, Des Moines, Iowa, USA
References: <70423@hydra.gatech.EDU>
Date: Thu, 8 Oct 1992 20:13:07 GMT

>
> Here is my program SNAKE.  All of my vampiric bombers kept taking
> a beating from this new class of bombers that claim to bomb
> the core at 150% of c.  But a decrement doesn't kill a program.
> I designed all of the B-fields so that if any one is decremented,
> the bombing routine keeps functioning.
> 
> I would really be interested in any other programs that use
> this tactic.

AhHa!  So that's why Snake does so well against my bombers.

I wondered if people would catch on to this.  It's easy to protect
against single decrements on b-fields.  Here's how I do it in Eclipse:
Lines marked ** function normally when decremented (once).

;redcode
;name Eclipse V2.0
;kill Eclipse
;author P.Kline
;strategy bscan, 2-dwarf, 1-dwarf
bomb2    mov -1,<0
ptr      mov bomb1,<1-131
next     add #121,@2         ; **
         jmz next,@ptr
         mov bomb2,@ptr
         jmn ptr,@-1         ; **
bomb1    spl 0,10            ; **
         mov cnt+1,<bomb1-2  ; **
         mov cnt+3,<bomb1-3  ; **
cnt      djn -1,@0           ; **  stays zero until decremented or executed
         end next

Here's another tip.  Don't put zeros in any b-fields in your code.
Since the bomber is doing:
    mov <a,<b
if a points to your zero-value, no problem, but if b does,
the location just ahead of it will be bombed.  Better to make it
something large.  This also applies to locations following your
code.  Better make them something other than zero too. 
Course that leaves you open to probing by b-scanners . . .

Unfortunately, all this anti-stone technology is only going to help scanners.

Paul Kline
pk6811s@acad.drake.edu