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Multiplication of binary numbers

#1
04-02-2024, 08:24 PM
I recall how binary multiplication works when you multiply two numbers bit by bit. You shift left each time you hit a one in the multiplier. Then add up those partial products right away. It feels simple once you try it on paper a few times. But hardware does it with adders and shifters wired together. You see the pattern emerge fast in small examples like four bit values.
And perhaps you notice how zeros just skip the add step entirely. That saves cycles in the processor unit. I tried explaining it to my buddy last week over coffee. He got stuck on the carry bits though. Now you can think of it like long multiplication but only with ones and zeros. Each position doubles the weight as you move left. Or maybe you handle the sign bit separately if numbers go negative. That changes things in two complement setups.
But you keep the flow going by generating all partial rows first. Then sum them column wise with full adders. I found that method avoids overflow surprises in bigger words. You end up with the product in the accumulator register after shifts. Also perhaps the array multiplier builds it all in parallel for speed. That uses more gates but cuts down latency a lot. I like how it scales when you add pipeline stages.
Now you might wonder about Booth encoding to cut down adds. It groups bits and skips some operations cleverly. I saw it speed things up in older CPUs during tests. You apply the rules by looking at pairs of bits each cycle. Or then you subtract instead of add when you hit certain patterns. That reduces the total partial products you need. I remember testing it on eight bit numbers and seeing fewer steps.
But you have to watch for the correction at the end if signs differ. It keeps the result accurate without extra hardware sometimes. Perhaps you combine it with Wallace trees for even faster summing. Those compress the columns using carry save tricks. I played around with it in simulations and got lower delays. You notice the tradeoffs between area and performance right away.
Also maybe you consider sequential multipliers for low power designs. They reuse one adder over multiple cycles. I think that fits embedded stuff where space matters most. You load the operands then loop through the bits. Or then you accumulate the result bit by bit. That way avoids big combinational logic clouds. I always check the timing diagrams to verify no glitches pop up.
You see how overflow flags trigger if the high bits exceed the word size. I caught that error once during a debug session with friends. Now you handle fractions too by tracking the point position. It works similar but with right shifts instead. Perhaps you extend to floating point by normalizing mantissas first. That adds exponent adds into the mix. I enjoy breaking it down step by step like this.
But you practice with random values to build intuition quick. I did that and it stuck better than reading alone. You avoid mistakes by verifying the decimal equivalent after. Or then you tweak the algorithm for specific architectures. That keeps things efficient in real chips. I share these ideas because they helped me early on.
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ron74
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Multiplication of binary numbers - by ron74 - 04-02-2024, 08:24 PM

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Multiplication of binary numbers

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