how can i have one precomputation unit and THEN for process that happening concurrent

hi
i want to a precomputation first and then do 4 part that are happening concurrent ???
i think to put that 4 part in 4 process that are donig concurrent but i dont know how to do the precomputation part before this for parts??

You really need to go read a book firstly on digital logic design (Paying particular attention to the words synchronous and combinatorial), then on VHDL, EVERYTHING is concurrent unless you force it to not be.

The keyword is pipelining, create an entity containing your preprocessing logic, register the output and then hook it to your main processing blocks, you may wish to provide a 'data valid' strobe to the processing blocks from the preprocessor.

At any given time the preprocessor logic is computing the data to be handed off to the processing blocks on the rising edge of the NEXT clock pulse, while at the same time the processing blocks are calculating outputs based on the output of the preprocessor which changed at the last rising edge of the clock.

This is very, very standard stuff.

Regards, Dan.

i dont know how to put preprocessor logic in entity, ithout we can not put anythind except input and output in entity?

You really really need to read a digital logic design book.
the pre-processor he is refering to is part of your algorithm. With proper design and pipelining, the pre-processor can work at the same time as the other parts - because the data arrives serially.