exit Statements

The exit statement completes execution of an enclosing loop statement, called label in the syntax. The completion is conditional if the statement includes a condition, such as the when condition in the following syntax.

exit [ label ] [ when condition ] ;

• label: An exit statement with no label terminates the innermost enclosing loop. When you specify a loop label, the current iteration of than named loop is terminated, as shown in the previous example of a named next statement.
  
  
• when is an optional clause that executes its next statement when its condition (a Boolean expression) evaluates TRUE.
  
  

  Note: The exit and next statements have identical syntax, and they both skip the remainder of the enclosing (or named) loop. The difference between the two statements is that exit terminates its loop and, then, continues with the next loop iteration (if any).

The example below compares two bit vectors. An exit statement exits the comparison loop when a difference is found. The corresponding circuit design is shown in the figure following this example.

entity example5 16 is

   port(

      signal A, B: in BIT_VECTOR(1 downto 0);

      signal A_LESS_THAN_B: out Boolean;

      );

end example5 16;

architecture behave of example5 16 is

begin

process (A, B)

begin

A_LESS_THAN_B <= FALSE;

for I in 1 downto 0 loop

  if (A(I) = '1' and B(I) = '0') then

    A_LESS_THAN_B <= FALSE;

    exit;

  elsif (A(I) = '0' and B(I) = '1') then

    A_LESS_THAN_B <= TRUE;

    exit;

  else

    null;      -- Continue comparing

  end if;

end loop;

end process;

end behave;

Figure 5.8 Circuit Design for Comparator Using the exit Statement