Re: Thoughts in combinatorial logic

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From	Sylvia Else <sylvia@email.invalid>
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Subject	Re: Thoughts in combinatorial logic
Date	Wed, 3 Apr 2019 09:34:55 +1100
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On 3/04/2019 9:11 am, Bruce Horrocks wrote:
> Can you explain a bit more, please?
> 
> 
> On 01/04/2019 06:11, Sylvia Else wrote:
>> As part of a personal project I'm working on, I needed a combinatorial 
>> logic way of obtaining the lowest set bit from a collection of bits. 
>> That is, taking n inputs in some order, and by using only and/or/not 
>> gates, produce n outputs of which only one is set, being that which 
>> corresponds to the lowest order set input bit
> 
> So a filter that allows the lowest set bit through and clears any higher 
> set bits?

Yes.

> 
>>
>> It's not especially difficult.
>>
>> But suppose the requirement is not the lowest set bit, just any of the 
>> set bits.
> 
> What do you mean by 'any'? A filter that randomly selects one of the set 
> bits to be allowed through?

It could be random, in principle, though combinatorial logic is unlike 
to have that outcome.

Rather stating the obvious, if one assumes that a simpler solution 
exists to the second requirement, then there must be situations where 
changes to the inputs produces changes to the outputs that differ for 
the solution to the first require and the second requirement. I've put 
some thought into a reductio-ad-absurdum proof based on that, but made 
little progress.

Of course, a proof is not going to be forthcoming if my intuition is 
just wrong.

Sylvia.

Thread

Thoughts in combinatorial logic Sylvia Else <sylvia@email.invalid> - 2019-04-01 16:11 +1100
  Re: Thoughts in combinatorial logic Marko Rauhamaa <marko@pacujo.net> - 2019-04-01 16:28 +0300
  Re: Thoughts in combinatorial logic not@telling.you.invalid (Computer Nerd Kev) - 2019-04-02 22:08 +0000
    Re: Thoughts in combinatorial logic not@telling.you.invalid (Computer Nerd Kev) - 2019-04-03 07:47 +0000
  Re: Thoughts in combinatorial logic Bruce Horrocks <07.013@scorecrow.com> - 2019-04-02 23:11 +0100
    Re: Thoughts in combinatorial logic Sylvia Else <sylvia@email.invalid> - 2019-04-03 09:34 +1100
  Re: Thoughts in combinatorial logic Bruce Horrocks <07.013@scorecrow.com> - 2019-04-05 10:48 +0100
    Re: Thoughts in combinatorial logic Sylvia Else <sylvia@email.invalid> - 2019-04-11 20:33 +1000

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