urlencode urldecode in pure bash as efficient as possible

urlencode.sh

#!/bin/bash
# urlencode / urldecode in pure bash without externals
# no backticks or forking, all in-memory ops
# urlencode/urldecode the contents of $x, place results back in $x
# allow bash-isms
# b.kenyon.w@gmail.com

urlencx () {
  local LANG=C i b t=$x l=${#x} ;x=''
  for ((i=0;i<l;i++)); do
    b=${t:i:1}
    [[ "$b" =~ [a-zA-Z0-9\.\~\_\-] ]] || printf -v b '%%%02X' "'$b"
    x+=$b
  done
}

urldecx () {
  local LANG=C
  x="${x//+/ }"
  printf -v x '%b' "${x//%/\\x}"
}

printf -v x "This'll be fun\!\n*Won't* \"it\"?"

printf 'original: x="%s"\n' "$x"
urlencx
printf ' encoded: x="%s"\n' "$x"
urldecx
printf ' decoded: x="%s"\n' "$x"