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Agreeing floating inputs pass through an unknown select · case 04

Two candidate inputs both at 'z' produce 'z' instead of 'x'.

Member previewVariant 4 · 3 implementations · 9 checks per implementation

Case contract

Input [kind, sel, data]: sel is MSB-first over 0/1/x/z; an x or z select bit makes both values of that bit candidates. mux: the output is the common value of all candidate data inputs if they agree and are 0 or 1, else 'x'. dec: data[0] is the enable; enable 0 gives all '0'; otherwise candidate lines are '1' only when there is a single candidate and the enable is 1, else 'x'; non-candidate lines are '0'.

Why this case matters

Unknown-select pessimism rules in RTL simulation decide whether X on a control input corrupts datapath outputs.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
mux unknown select floating data	`"z"`	`"x"`	Failed

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