# Factorial function with logic.

Discussion in 'Digital Circuit Design' started by Mr.Alan, Jun 10, 2017.

1. ### Mr.Alan Thread Starter New Member

Aug 15, 2016
11
0
Hi. I would realy know a way to do factorial function (!) with some kind of circuit with 8-bit data output.

2. ### Papabravo Expert

Feb 24, 2006
11,994
2,574
This is not very hard. You use a lookup table with a 3-bit input and 8-bit output. All FPGA development tools will synthesize this function. The lookup table produces the following results:

0! = 1 = 0b0000 0001
1! = 1 = 0b0000 0001
2! = 2 = 0b0000 0010
3! = 6 = 0b0000 0110
4! = 24 = 0b0001 1000
5! = 120 =0b0111 1000
6! = OVERFLOW = any convenient value that is not equal to one of the above outputs
7! = OVERFLOW = any convenient value that is not equal to one of the above outputs

And we're done.

Last edited: Jun 10, 2017
#12 and AnalogKid like this.
3. ### #12 Expert

Nov 30, 2010
18,076
9,678
That sure beats trying to teach a machine how to multiply!

4. ### GopherT AAC Fanatic!

Nov 23, 2012
7,983
6,775
You do realize there are only 6 possible output values that Can be possible if you are limited to 8-bit values.