Back in 386 era, there was a concept of self-modifying code (assembly). A similar like stencils presented here, but because code was a singleton, rarely a copy

Back in 386 era, there was a concept of self-modifying code (assembly). A similar like stencils presented here, but because code was a singleton, rarely a copy was made. E.g. Doom on DOS used this optimisation techique, because otherwise you could not cram out enough performance from tight rendering loops on old CPUs.