Two's compliment of SIGNED binary

[fractal01]

The twos compliment for regular binary numbers- you just replace all 1's by 0's and 0's by 1's and then +1. So how would you go about finding out for signed...I have got as far as changing the first digit then that's it! Does anyone know what to do?

 

[I like Serena]

Hi fractal01!

"Signed" is the same thing (at least in 2's complement, which is pretty standard).

Suppose you take the number 1.
The binary representation is: 0001
The 2's complement is 1110+1=1111.
This is the same as the representation for -1.

Suppose you add them:
0001 + 1111 = (1)0000.

Yes! It is zero! (disregarding the carry over)

 

[fractal01]

Hi fractal01!

"Signed" is the same thing (at least in 2's complement, which is pretty standard).Yes! It is zero! (disregarding the carry over)

Hey! Thank you so much! My lecturer gave us some questions and in one of the answers he came up with something completely different and it was the only example so I have been struggling over it for at least half an hour! Everyone is human I guess and makes mistakes...but are you sure that this is the only way of calculating this?

 

[I like Serena]

...but are you sure that this is the only way of calculating this?

This is the way the 2's complement representation and its associated "signed" works.

There are other representations, such as 1's complement (unusual), and a representation with a separate sign bit (used for floating point), but those are not "regular" binary numbers.

So what did your lecturer come up with?

 

[aralbrec]

It could be sign-magnitude representation.

 

[I like Serena]

It could be sign-magnitude representation.

That's what I said or what I at least intended:
"a representation with a separate sign bit (used for floating point)"

 

[fractal01]

That's what I said or what I at least intended:
"a representation with a separate sign bit (used for floating point)"

Thanks for all of your help! You are right. He just looked at a different question when he was writing the problem I think.

 

[fractal01]

It could be sign-magnitude representation.

Thanks