Difficulty: Easy · Puzzle 6 of 6 · Topic: Datatype and Bit Puzzles
For this value with an unknown bit, what do `==`, `===`, and `==?` return?
module p6;
logic [3:0] v = 4'b10x1;
initial begin
$display("eq=%b", v == 4'b1001);
$display("caseeq=%0d", v === 4'b10x1);
$display("wild=%0d", v ==? 4'b1??1);
end
endmodule`===` is exact 4-state match. `==?` treats wildcard bits in the pattern (RHS) as don't-care.
1) `v == 4'b1001` returns x because the x bit affects normal logical equality.
2) `v === 4'b10x1` returns 1 because every bit, including x, matches exactly.
3) `v ==? 4'b1??1` returns 1 because RHS `?` bits are don't-care and only MSB/LSB are checked.Answer: eq=x, caseeq=1, wild=1
A common mistake is treating `==?` like `===` or assuming wildcarding happens on both operands.
What would `v ==? 4'b0??1` return, and why?