namespace Utf8 { // could be a static class, instead of a namespace, if it needs private members
// basic classification of UTF-8 bytes
inline static bool isSingleByte(UCHAR c)       { return c < 0x80; }
inline static bool isPartOfMultibyte(UCHAR c)  { return c >= 0x80; }
inline static bool isFirstOfMultibyte(UCHAR c) { return c >= 0xC2 && c < 0xF5; } // 0xF5 to 0xFD are defined by UTF-8, but are not currently valid Unicode
inline static bool isContinuation(UCHAR c)     { return (c & 0xC0) == 0x80; }
inline static bool isValid(UCHAR c)            { return c < 0xC0 || isFirstOfMultibyte(c); } // validates a byte, out of context

// number of continuation bytes for a given valid first character (0 for single byte characters)
inline static int  continuationBytes(UCHAR c)  {
 static const char _len[] = { 1,1,2,3 };
 return (c < 0xC0) ? 0 : _len[(c & 0x30) >>  4];
}

// validates a full character
inline static bool isValid(const char* buf, int buflen) {
 if(isSingleByte(buf[0])) return true; // single byte is valid
 if(!isFirstOfMultibyte(buf[0])) return false; // not single byte, nor valid multi-byte first byte
 int charContinuationBytes = continuationBytes(buf[0]);
 if(buflen < charContinuationBytes+1) return false; // character does not fit in buffer
 for(int i = charContinuationBytes; i>0; --i)
  if(!isContinuation(*(++buf))) return false; // not enough continuation bytes
 return true;  // the character is valid (if there are too many continuation bytes, it is the next character that will be invalid)
}

// rewinds to the first byte of a multi-byte character for any valid UTF-8 (and will not rewind too much on any other input)
inline static int characterStart(const char* buf, int startingIndex) {
 int charContinuationBytes = 0;
 while(charContinuationBytes < startingIndex // rewind past start of buffer?
  && charContinuationBytes < 5 // UTF-8 support up to 5 continuation bytes (but valid sequences currently do not have more than 3)
  && isContinuation(buf[startingIndex-charContinuationBytes])
  )
  ++charContinuationBytes;
 return startingIndex-charContinuationBytes;
}
};