bool utf8check5(const char *_s, int len)
{
	const byte *s = (const byte *)_s;
	const byte *lim = s + len;
	int codePoint = 0;
	while(s < lim) {
		word code = (byte)*s++;
		if(code >= 0x80) {
			if(code < 0xC2)
				return false;
			else
			if(code < 0xE0) {
				if(s >= lim || *s < 0x80 || *s >= 0xc0)
					return false;
				codePoint = ((code - 0xC0) << 6) + *s - 0x80;
				if(codePoint < 0x80 || codePoint > 0x07FF)
					return false;
				s++;
			}
			else
			if(code < 0xF0) {
				if(s + 1 >= lim ||
				   s[0] < 0x80 || s[0] >= 0xc0 ||
				   s[1] < 0x80 || s[1] >= 0xc0)
				   	return false;
				codePoint = ((code - 0xE0) << 12) + ((s[0] - 0x80) << 6) + s[1] - 0x80;
				if(codePoint < 0x0800 || codePoint > 0xFFFF)
					return false;
				s += 2;
			}
			else
			if(code < 0xF5) {
				if(s + 2 >= lim ||
				   s[0] < 0x80 || s[0] >= 0xc0 ||
				   s[1] < 0x80 || s[1] >= 0xc0 ||
				   s[2] < 0x80 || s[2] >= 0xc0)
				   	return false;
				codePoint = ((code - 0xf0) << 18) + ((s[0] - 0x80) << 12) + ((s[1] - 0x80) << 6) + s[2] - 0x80;
				if(codePoint < 0x010000 || codePoint > 0x10FFFF)
					return false;
				s += 3;
			}
			else
				return false;
		}
	}
	return true;
}