# A question about the logic of certain transformations

1. May 1, 2008

### transgalactic

there is this table that i showed in my previos question
now i need to implement it using 16X4 and 4 X4 proms

here is the table:

http://s290.photobucket.com/albums/ll279/transgalactic/?action=view&current=IMG_8814.jpg

here is the table:

http://s290.photobucket.com/albums/ll279/transgalactic/?action=view&current=IMG_8815.jpg

my problem is with the #1 and the #2 components

regarding the #1 component:
its input is the two's complement of a certain number X
and the output is the |X|

i know that in order to transform a normal number into its two's complement
we need to flip each digit and add one to the resolt

we are required to do the oppossite thing ,so we need to subtract one
and flip each digit
but they did something odd (int the #1 component)

in part A marked red they didnt transform at all the numbers
but in part B marked blue instead of subtracting one and plipping each digit
they found the two's complement of the input number
why?????????????

regarding component #2:
i have the same problem but here in group D they flip each digit
were as in part C they live it as it is

there is some logic behind that
i cant see it??