a question about base 3 subtruction..

[transgalactic]

i cant understand how it works:
i have two bit numbers (x1 x0 ,y1 y0) which are needed to be subtruction

i cant understand why
x1 x0 y1 y0 | B D1 D2
0 0 0 1 | 1 1 0
0 0 1 0 | 1 0 1
0 0 1 1 | X X X


i cant understand these arithmetics
the first one is 0-1=-1
so in base 3 the resolt is should be three but i cant understand what meen Borrow=1
and the resolt 10
i dont understand how did they desided that

and why we have dont cares on the third example

 

[Pommie]

First, this is base 2 arithmetic, also called binary arithmetic. The columns go (right to left) units,2s,4s,8s,16s... just like base ten, which is units,10s,100s,1000s - we multiply by the base to move left a column. When we subtract a 1 from a zero it can't be done (same in base 10) and so we have to borrow 1 from the 2s column. So, 2-1=1 or in binary 10-01=01. We carry on subtracting each column until we have an answer.

For more information google binary arithmetic.

Mike.

 

[transgalactic]

the answer in the example you showed is
b=1 d1=1 d0=0

but you say it should be b=1 d1=0 d0=1

and what about the dont care case


?????//

 

[Pommie]

I don't understand your table. I was explaining the 0-1=-1 and why this needs to borrow one from the twos column.

Did you try googleing?

Mike.

 

[transgalactic]

ye i understood this stuff

i cant understand this table
espessioly the dont care case

maybe it differs because its base 3
???

 

[Pommie]

If it was base 3 it would also contain 2s and 10-1 would equal 02. It is binary.

Mike.

 

[transgalactic]

okkk
the solution needs to be in base thre
here is the original page of the solution

https://img411.imageshack.us/my.php?image=img8811or9.jpg

in the case of 0-3
it
000
-
011
we need to borrow out of the range so it will turn into

112
-
011
it gives us 101 (is it correct??)
not a three dont cares
i cant understand this last case
???????