# Designing an ALU: problem with multiplication operation

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#### amira

##### Newbie level 6 Hello everyone,

I have been trying to design a 4 bit ALU. I have designed it for some arithmetic and logical operations. Now I want to add the multiplication operation with my design. For that I am trying to design 4*4 multiplier. But the problem is it's giving me 7 outputs and the rest of the arithmetic and logical outputs are of 4 bits. So when I'll try to add my outputs in some mux , then there are 7 outputs from the multiplier and 4 outputs from the other portion.

If I use 4, 2*1 mux then there are 3 other multiplication outputs are left. What should I do in such a situation?

Any kind of suggestions will be greatly apperciated.

Thanks,

amira

#### WA

##### Member level 4 If I read this post correctly, You might be experiencing overflow conditions.

Also ALU's usually do the add/shift method. So by the inherent design the answer
shifts also

a quick example

4 * 2 = 8

4 = 0100
2 = 0010

If the ALU does the shift/add the output would look something like this

0001000 it's still the same answer but you have 3 added bits to the begining.

hope this helps a little
wa

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