UTF-8 Hex String(of 1character) To Unicode code point value

getCodePoint.js

/*-----------------------------------------------------------------------------------------
[UCS-2 (UCS-4)]     [codepoint bit pattern]   [1st byte]  [2nd byte]  [3rd byte]  [4th byte]
U+ 0000..  U+007F    00000000-0xxxxxxx         0xxxxxxx
U+ 0080..  U+07FF    00000xxx-xxyyyyyy         110xxxxx    10yyyyyy
U+ 0800..  U+FFFF    xxxxyyyy-yyzzzzzz         1110xxxx    10yyyyyy    10zzzzzz    
U+10000..U+1FFFFF    00000000-000wwwxx         11110www    10xxxxxx    10yyyyyy    10zzzzzz
                    -xxxxyyyy-yyzzzzzzz
------------------------------------------------------------------------------------------*/
// e.g.
// [in]  0xC6A9 ('Σ', U+01A9)
// [out] 0d0425 (=0x1A9)
function getCodePoint(hex) {
	var bytes, n, shift1st, codePoint;
	// requires less than 4bytes
	bytes = Math.floor(Math.log(hex) / Math.log(0xFF) + 1);
	if (bytes > 4) {
		return -1;
	}
	// mask 1st byte
	shift1st = (bytes === 1) ? 0 : (bytes + 1);
	codePoint = (hex >> ((bytes - 1) * 8)) & (0xFF >> shift1st);
	for (n = 1; n < bytes; n++) {
		codePoint <<= 6;
		// 2nd-4th byte: mask 0x00111111
		codePoint += (hex >> ((bytes - 1 - n) * 8)) & 0x3F;
	}
	return codePoint;
}