If the real code is in the context of a sub then the following is clearer and less error prone:

return 18 if $major_length == 4800;

if ($major_length == 8552) {
   return 33 if $val == 4;
   return 18 if $val == 1;
   return "Bogus value ($val) for major length $major_length";
} else {
   return "Bogus major length ($major_length)";
}
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