Hexadecimal Multiplication using 2's complement

[Fatima Hasan]

Homework Statement

Perform the following operations using 2's complement method.
$FFFD_{16} * FFF1_{16}$

Homework Equations

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The Attempt at a Solution

$FFFD_{16}$ ----> (1's comp.) = $0002_{16}$ -----> (2's comp.) = $0003_{16}$
$FFF1_{16}$ ----> (1's comp.) = $000E_{16}$ -----> (2's comp.) = $000F_{16}$
$0003_{16} * 000F_{16} = D2_{16}$

But $FFFD_{16}$ ( negative ) * $FFF1_{16}$ ( negative ) , so the answer should be positive .
The answer is $= 0D2_{16}$ (positive ) .
Could anyone check my answer please ?

 

[phinds]

what is D2 base 16 in decimal? Does it sound like the right answer for 3x15?

 

[Fatima Hasan]

what is D2 base 16 in decimal? Does it sound like the right answer for 3x15?

$2D_{16}$

 

[phinds]

$2D_{16}$

Did you not understand my question? What is that in DECIMAL base?

 

[Fatima Hasan]

Did you not understand my question? What is that in DECIMAL base?

$D2_{16} = 13 * 16 + 2 * 16^0$
$= 210$
It's not the right answer for 3*15 .
I tried to solve the problem again and this is my work :
$3 * 15 = 45$ in decimal which is equal to $2D_{16}$
So, $FFFD_{16}$ ( negative ) * $FFF1$ (negative) = $02D_{16}$

 

[phinds]

$D2_{16} = 13 * 16 + 2 * 16^0$
$= 210$
It's not the right answer for 3*15 .
I tried to solve the problem again and this is my work :
$3 * 15 = 45$ in decimal which is equal to $2D_{16}$
So, $FFFD_{16}$ ( negative ) * $FFF1$ (negative) = $02D_{16}$

Yes, and can you do the actual arithmetic in base 16? (I wouldn't bother but I'm not sure if that's part of what you are supposed to do)

 

[phinds]

I solved it again and I got $2D_{16}$ not $D2_{16}$.

Yes, I deleted the post where I mistakenly said it 2D was wrong. I got the 2D confused with the D2

 

[Fatima Hasan]

Yes, and can you do the actual arithmetic in base 16? (I wouldn't bother but I'm not sure if that's part of what you are supposed to do)

3 * F (15 in decimal) = 45 in decimal.
45 / 16 = 2.8125 ( 2 is the first digit , subtract 2 from 2.8125 and multiply the answer by 16 to get the second digit which is 13 in decimal ( D in base 16 ).

 

[phinds]

3 * F (15 in decimal) = 45 in decimal.
45 / 16 = 2.8125 ( 2 is the first digit , subtract 2 from 2.8125 and multiply the answer by 16 to get the second digit which is 13 in decimal ( D in base 16 ).

No, I mean can you do the original problem FFFD*FFF1 IN HEX not in decimal. I don't know that it's a requirement of the problem, I'm just asking if you CAN do it. Anyway, I think I've given you what help I can with this problem so I'll bow out now.

 

[hmmm27]

No, I mean can you do the original problem FFFD*FFF1 IN HEX

yes, but it's annoying and requires twice the register space and use of a rubber chicken to do it flat out instead of as complements.

 

[NascentOxygen]

But $FFFD_{16}$ ( negative ) * $FFF1_{16}$ ( negative ) , so the answer should be positive .
The answer is $= 0D2_{16}$ (positive ) .
Could anyone check my answer please ?

Is this all solved now, Fatima Hasan? The only problem being that you have been writing D2 where you meant to write 2D?