how many "1" in input data?

[vongy]

please help me how to cacl the number ''1' in the input data in only one clock cycle?
for example:
if input [31:0] = 32'hf then output data = 4;
if input [31:0] = 32'7f then output data = 7;

please not use too many adder !
please not use for loop!

thanks

 

[lostinxlation]

It's actually easy, but seems line a home work and I'll give you only a hint.
Draw a truth table of a full adder and look at it very carefully.

 

[rca]

why not using loop & adder? easy to use and readable

variable_cnt := 0;
for i in 0 to 31 LOOP
if vector_input(i)='1' then
variable_cnt := variable_cnt + 1;
end if;
end for;

 

[vongy]

It's actually easy, but seems line a home work and I'll give you only a hint.
Draw a truth table of a full adder and look at it very carefully.

thanks, but it is not a homework!!!
I know i must use adder, but i want to use the least resource!!

---------- Post added at 04:12 ---------- Previous post was at 04:10 ----------

why not using loop & adder? easy to use and readable

variable_cnt := 0;
for i in 0 to 31 LOOP
if vector_input(i)='1' then
variable_cnt := variable_cnt + 1;
end if;
end for;

thanks.
Yes, this easy to readable, but it has 32 fulladder in series, how i can calc it in 5ns, my system run on 200MHz clock domain, and i must calc it in only one cycle!!

 

[lostinxlation]

I told you what to do. Have you ever CAREFULLY and RIGOROUSLY looked at the truth table of full adder ?

Open your eyes real wide and look at the truth table. Doesn't notice anything ? if so, think about rearranging the table. Or better yet, consider what a binary full adder means mathematically.

A B Ci    S  Co
-----------------
0 0 0     0   0
0 0 1     1   0
0 1 0     1   0
0 1 1     0   1
1 0 0     1   0
1 0 1     0   1
1 1 0     0   1
1 1 1     1   1

This is one of weakness of today's digital engineer. They rely too much on RTLs and forgot the nature of binary operation.


PS. I quickly made a few logics. Apparently you need 4 adders to count 1 in 6 bits, 4 adders for 7 bits, 7 adders for 8 bits.. And it seem counting 1 in 32 bits requires 31 adders with only 8 levels of adders at the critical paths so that it will meet 5ns though I don't know which process you are using.