Velocity Reviews > VHDL > Fractions

# Fractions

Iqbal
Guest
Posts: n/a

 04-10-2007
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
Guest
Posts: n/a

 04-10-2007
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

"Iqbal" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> 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
>

Thomas Stanka
Guest
Posts: n/a

 04-10-2007
On 10 Apr., 12:19, "Iqbal" <(E-Mail Removed)> wrote:
> 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