Hardware interview practice
Count active lanes in a predicate mask
Implement a combinational population-count unit for a statically sized predicate mask. The result must represent every value from zero through WIDTH.
Reviewed example
Work through one case
Input
WIDTH=5; predicate mask=5'b10111Expected output
count=3'b100 (4 active lanes)$clog2(5+1)=3 result bits represent the all-active value five without truncating the four counted ones.
What to cover
Requirements
- Support any static WIDTH >= 1, including non-powers of two.
- Size the result with $clog2(WIDTH + 1) so the all-ones answer is representable.
- Do not use a simulation-only system task as the implementation.
- Assign the accumulator on every evaluation and avoid truncated intermediate results.