color-hash.ksh: provide a fnv1a implementation and switch to it

utils/scripts/color-hash.ksh

@@ -11,14 +11,36 @@ function _color_hash_djb2
 	print $h
 }
 
+function _color_hash_fnv1a
+{
+	local c h s
+	s=$1
+	h=${2:-2166136261}
+	while (( ${#s} > 0 )); do
+		c=0x${s%${s#??}}
+		s=${s#??}
+		h=$(( $h ^ $c ))
+		h=$(( (($h << 24) + ($h << 8) +
+		    ($h << 7) + ($h << 4) + ($h << 1) + $h) & 0xffffffff ))
+	done
+	# xor-fold to 16 bits
+	print $(( ($h >> 16) ^ ($h & 0xffff) ))
+}
+
 function color_hash
 {
-	local bright flag h n s
+	local bright impl flag h n s
 
 	bright=false
-	while getopts b flag; do
+	impl=_color_hash_fnv1a
+	while getopts bi: flag; do
 		case $flag in
 		b)	bright=true ;;
+		i)	if [[ $OPTARG != @(djb2|fnv1a) ]]; then
+				return 1
+			fi
+			impl=_color_hash_$OPTARG
+			;;
 		*)	return 1 ;;
 		esac
 	done
@@ -27,7 +49,7 @@ function color_hash
 	h=
 	s=$(print -nr "$1" | od -A n -t x1 | tr -d '[:space:]*')
 	while :; do
-		h=$(_color_hash_djb2 "$s" $h)
+		h=$($impl "$s" $h)
 		# Avoid modulo bias.
 		(( $h >= 4 )) && break
 	done