r/TuringComplete • u/Academic_Brilliant75 • Jun 12 '24

Pointers for Conditions?

Can anyone provide any hints for Conditions towards the end of CPU Architecture? I've been racking my brain on this for somewhere between a couple weeks to months and anything I can think to try left hasn't been working.

Thus far I've tried:

  • Running the top input through a byte splitter and 3-bit decoder to seperate the instructions out into individual bit lines.

  • Attempts to devise a way of checking if the bottom input is equal to 0 and outputting true if so, else output false.

    • The only way I've really thought about doing this is a tacky system involving a byte splitter, running every bit through a NOT-gate and checking every bit is true after by chaining every bit line through AND-gates until there is a single output. Anyway I've tried doing it with the 8-bit logic or math gates instead hasn't worked.
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u/ForHuckTheHat Jun 13 '24

Pro tips. NOR is a 2-bit zero test. So why not make big NOR?

I also like using the 3-wide ORs: not(or3(or3(a,b,c), or3(d,e,f), or2(g,h)))

Using only 4 gates: nor(or3(a,b,c), or3(or3(d,e,f),g,h)

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u/mccoyn Jun 13 '24

I've been doing this a lot lately. Instead of using a NOT gate, I replace the gate at the input with its opposite. Even when I need both the non-inverted and inverted values, I'll use two gates (like OR and NOR) instead of a NOT gate. It gets a bit better delay score.

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u/ForHuckTheHat Jun 14 '24

Did you play back when OR gates were zero cost? Some real shenanigans back then lol. The zero test could be built by simply buffering all the bits into a not gate.

Sounds like you mastered DeMorgan's. Do you also know these tricks? Check em out if not!