djb2 hash implementation in portable shell

djb2.sh

set -euf
IFS=''
LC_ALL=C

! command -v emulate >/dev/null 2>&1 || emulate ksh >/dev/null 2>&1
command -v local >/dev/null 2>&1 || alias local=typeset

_ordchr_='\015\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037\040\041\042\043\044\045\046\047\050\051\052\053\054\055\056\057\060\061\062\063\064\065\066\067\070\071\072\073\074\075\076\077\100\101\102\103\104\105\106\107\110\111\112\113\114\115\116\117\120\121\122\123\124\125\126\127\130\131\132\133\134\135\136\137\140\141\142\143\144\145\146\147\150\151\152\153\154\155\156\157\160\161\162\163\164\165\166\167\170\171\172\173\174\175\176\177\'
_ordchr_="$(printf "$_ordchr_")"

_subs () {
    local str="$1" i=0 from=$(($2)) to=$(($3 + $2)) sub=
	while test $i -lt $to
	do
		rest="${str#?}"
		char="${str%"$rest"}"
		str="${rest}"
        test $from -gt $i || sub="$sub$char"
        i=$((i + 1))
    done
    _r="$sub"
}

_ord () {
    _r="${_ordchr_%$1*}"
    _r=${#_r}
}

_chr () {
    _subs "$_ordchr_" $1 1
}


_djb2_hash () {
    local num="$1" hash=5381
	while test ${#num} -gt 0
	do
		rest="${num#?}"
		char="${num%"$rest"}"
		num="${rest}"
        _ord "$num"
		hash=$(((hash + (hash << 5)) ^ _r))
	done
    echo $hash
}

_djb2_hash "the quick brown fox"
_djb2_hash "the quick brown fox2"
_djb2_hash 'b'