guideline

Use hard-coded constraint checking when measured performance indicates.

   subtype Small_Int is Positive range Lower .. Upper;
   Var : Small_Int;
   ...

   -- Using exception handler
   Double:
      begin
         Var := 2 * Var;
      exception
         when Constraint_Error =>
            ...
      end Double;

      -- Using hard-coded check
      if Var > Upper / 2 then
         ...
      else
         Var := 2 * Var;
      end if;

rationale

Determine the impact of using exception handlers to detect constraint errors. If the exception handling mechanism is slow, then hard-coded checking may be more efficient.