Minecraft Maps / Redstone Device

8-Bit Kogge-Stone Adder [RDF]

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properinglish's Avatar properinglish
Level 32 : Artisan Engineer
34
I present to you my Kogge-Stone adder! Now, I love pistons and instant ripple-carry as much as anyone. In fact, the vast majority of my creations have relied on pistons for speed - and I've made some very fast circuits. The thing is, I thought it would be a lot of fun to start playing with some more complex logic and build a real life fast adder while taking a break from pistons.

You might have heard the terms "Kogge-Stone" or "carry-lookahead" before, and while the circuitry sure is convoluted, the concept isn't too hard to understand. In a ripple carry adder the carry is calculated as the sum is calculated, so you can't calculate the carry or sum of a bit until the carry of the previous bit has been calculated. A carry-lookahead adder produces the carry of each bit before the sum, so you have much less waiting to do. The Kogge-Stone Adder is a type of carry-lookahead adder with reduced fan-out (fan-out refers to the number of connections between a logic gate output and other logic gate inputs), making it quite fast. The one I built has a slowest speed of 9 ticks - not to shabby for a torch-based adder!


This was built on the Redstone Development Foundation Build Server - Come check us out at therdf.net!
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1
03/08/2012 5:15 am
Level 54 : Grandmaster Pirate
RevolutionalRedStone
RevolutionalRedStone's Avatar
9-Ticks is brilliant for an 8-bit adder.... Infact I'm taking this for something ; )
1
03/06/2012 9:42 am
Level 23 : Expert Geek
vanyamil
vanyamil's Avatar
GJ. I was trying to do a LCA too, but it was too slow. +1
1
03/06/2012 11:15 am
Level 32 : Artisan Engineer
properinglish
properinglish's Avatar
Thanks! :D The trick to making it fast was designing it so that the rate-limiting delay was in the logic, rather than in any bussing. Additionally, I used 2-tick XNOR gates as opposed to 3-tick XORs and managed to save a tick in the first layer of the lookahead logic (BK Cells) by using a NOR gate rather than an AND.
1
03/06/2012 5:28 pm
Level 23 : Expert Geek
vanyamil
vanyamil's Avatar
True that :D GJ
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