[akavel]

Though this argument also supports the parent comment actually: notably, standard library has much higher than usual chance and assumption of being possibly used in tight loops - with no way to relax that assumption based on actual (often closed-source) usage. So the same optimizations done in stdlib could perfectly well be considered premature if done in non-stdlib code (even if we imagined some func was not in stdlib and one needed to write exactly same func in one's code).