$4\mathrm{.}8$ Design a code converter that converts a decimal digit from

$($a$)*$ The $8,4,-2,-1$ code to BCD $($see Table $1\mathrm{.}5).($HDL$-$see Problem $4\mathrm{.}50)$

$($b$)$ The $8,4,-2,-1$ code to Gray code.