Both the default F80 softfloat wrappers (FXTRACT_SIG/FXTRACT_EXP) and
the reduced-precision F64 dispatcher fell through to the generic
exponent/significand extraction for Inf and NaN inputs, producing
finite garbage. The F80 wrapper returns input unchanged in the
significand slot and +Inf (or NaN) in the exponent slot; the F64
dispatcher detects the exponent-all-ones case and selects the proper
Inf/NaN result before the existing zero-case fold.