+utf16.adjust = function(mode, string, after) {
+ var before = after.slice();
+ var offset = 0, index = 0;
+
+ var check = function() {
+ var from = mode ? index : offset;
+ var to = mode ? offset : index;
+
+ for (var o = 0, l = after.length; o != l; ++o)
+ if (before[o] == from) {
+ before[o] = null;
+ after[o] = to;
+ }
+ };
+
+ for (var e = string.length; index != e; ++index) {
+ check();
+
+ var unit = string.charCodeAt(index);
+ var part = unit & 0xfc00;
+
+ if (part == 0xdc00)
+ return null;
+ else if (part != 0xd800);
+ else if (++index == e)
+ return null;
+ else {
+ var next = string.charCodeAt(index);
+ if ((next & 0xfc00) != 0xdc00)
+ return null;
+ }
+
+ ++offset;
+ }
+
+ check();
+ return after;
+};
+
+utf16.point2unit = function(string, offsets) {
+ return utf16.adjust(false, string, offsets);
+};
+
+utf16.unit2point = function(string, offsets) {
+ return utf16.adjust(true, string, offsets);
+};
+
+utf16.charAt = function(string, offset) {
+ return utf16.substring(string, offset, offset + 1);
+};
+
+utf16.charCodeAt = function(string, offset) {
+ var char = utf16.charAt(string, offset);
+ if (char.length != 2)
+ return char.charCodeAt(0);
+ return 0x10000 | (char.charCodeAt(0) & 0x03ff) << 10 | char.charCodeAt(1) & 0x03ff
+};
+
+utf16.strlen = function(string) {
+ return utf16.unit2point(string, [string.length])[0];
+};
+
+utf16.substr = function(string, start, length) {
+ var stop;
+ if (typeof length !== "undefined")
+ stop = start + length;
+ return utf16.substring(string, start, stop);
+};
+
+utf16.substring = function(string, start, stop) {
+ var range = utf16.point2unit(string, [start, stop]);
+ return string.substring(range[0], range[1]);
+};
+
+utf16.prototype.charAt = function(index) {
+ return new utf16(utf16.charAt(this.string, index));
+};
+
+utf16.prototype.charCodeAt = function(index) {
+ return utf16.charCodeAt(this.string, index);
+};
+
+utf16.prototype.substr = function(start, length) {
+ return new utf16(utf16.substr(this.string, start, length));
+};
+
+utf16.prototype.substring = function(start, end) {
+ return new utf16(utf16.substring(this.string, start, end));
+};
+
+utf16.prototype.toString = function() {
+ return this.string;
+};
+
+return utf16;
+