RosettaCodeData/Task/Substring-Top-and-tail/PARI-GP/substring-top-and-tail.pari

df(s)=concat(vecextract(Vec(s),1<<#s-2));
dl(s)=concat(vecextract(Vec(s),1<<(#s-1)-1));
db(s)=concat(vecextract(Vec(s),1<<(#s-1)-2));