Complete the line in the semaphore wait$()$ functions.

wait$($semaphore $*$S$)\{$

if $($S$->$value $\_\_\_\_\_\_\_\_0)\{$

S$->$value$--$;

add this process to S$->$list;

block$()$;

$\}$

else S$->$value$--$;

$\}$