DescriptionQ962
Q962DesignASIC interview problem
Count active lanes in a predicate mask
TechniquesPopulation countReductionWidth arithmetic
DifficultyEasy
TopicRTL Design
LanguageSystemVerilog
Requirements4 checkpoints
01
Problem
Implement a combinational population-count unit for a statically sized predicate mask. The result must represent every value from zero through WIDTH.
Example input and output
Use this case to check your interpretationInput
WIDTH=5; predicate mask=5'b10111Output
count=3'b100 (4 active lanes)Explanation
$clog2(5+1)=3 result bits represent the all-active value five without truncating the four counted ones.
02
Requirements (4)
- 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.