case condition is
when "1"=>
if input=A(1) then
output<=B(1);
else
output<=0;
when "2"=>
if input=A(2) then
output<=B(2);
else
output<=0;
when"3"
到when "98"
也是这规律
when "99"=>
if input=A(999) then
output<=B(99);
else
output<=0;
when others=>
output<=0;
end case;