8-Bit Population Counter (Popcount)

8-bit population count (popcount): counts the '1' bits in i_data and encodes the result as a 4-bit binary number (0 to 8).

Behaviour (pure combinational):

• o_count = i_data(0) + i_data(1) + ... + i_data(7) (arithmetic sum of the 8 bits).
• 4-bit output is enough since popcount(8 bits) ≤ 8 fits in 4 bits.

*No clock, no reset: pure combinational logic.*