guideline

Use the short-circuit control form when measured performance indicates.

   -- Nested "if"
   if Last >= Target_Length then
      if Buffer (1 .. Target_Length) = Target then
         ...
      end if;
   end if;

   -- "and then"
   if Last >= Target_Length and then Buffer (1 .. Target_Length) = Target then
      ...
   end if;

rationale

Determine the impact of using nested if statements versus using the and then or or else operator. One of the above may be significantly more efficient than the other.