Path: utzoo!mnetor!uunet!husc6!bbn!rochester!cornell!oravax!clay
From: clay@oravax.UUCP (McFarland)
Newsgroups: comp.lang.c
Subject: Re: XOR-trick and PUZZLE (was comma-operator)
Message-ID: <181@oravax.UUCP>
Date: 29 Jan 88 19:39:22 GMT
References: <cVyaqyy00jaBF6M0=4@andrew.cmu.edu>
Reply-To: clay@oravax.odyssey.UUCP (Clay Brooke-McFarland)
Organization: Odyssey Research Associates, Ithaca, New York
Lines: 23

In article <cVyaqyy00jaBF6M0=4@andrew.cmu.edu> bader+@andrew.cmu.edu (Miles Bader) writes:
>> How can you use the XOR trick to keep a doubly linked list, using only
>> one field for in each record, to code for finding both the following and 
>> the previous record?  
>
>To make it a bit clearer, you have to be able to find the NEXT record
>given the current and previous records, and find the PREVIOUS record
>given the current and the next record.

To make it a bit clearer all you have to do is XOR it with itself :-}

Of more interest, since you can store n things in a register and get
any of them back given the other n-1 you can store 
NEXT ^ PREVIOUS ^ KEY and keep the KGB from deciphering your linked
lists (Now where did I put that key...).


Clay Brooke-McFarland		    Odyssey Research Associates

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