Fractions

[Iqbal]

Hi all,

I need to do arithmetic using fractions eg. adding +1/4 of an 8 bit
value to another 8 bit value or subtracting
-1/16 of an 8 bit value from another 8 bit value.

Can anyone tell me how I can do this in VHDL or point me in the right
direction ?

Thanks

 

[Benjamin Todd]

Your examples are pretty simple, are you trying to make a generic 'fraction'
or is there only a certain set of values you can accept?

I'd be thinking about 1/(2^n) fractions as an approximation...

Considering that you only have an 8-bit number to start with, this means you
can only go from 0-255... this is probably an exploitable limitation.

Ben

 

[Thomas Stanka]

I need to do arithmetic using fractions eg. adding +1/4 of an 8 bit
value to another 8 bit value or subtracting
-1/16 of an 8 bit value from another 8 bit value.

Can anyone tell me how I can do this in VHDL or point me in the right
direction ?

Z= X + Y/4 for 8 bit unsigned:

Z <= X + "00"&Y(7 downto 2);

bye Thomas