#if TCL_UTF_MAX > 3
    4,4,4,4,4,
#else
    1,1,1,1,1,
#endif
    1,1,1,1,1,1,1,1,1,1,1
};

/*
 * Functions used only in this module.
 */

static int		Invalid(unsigned char *src);

/*
 *---------------------------------------------------------------------------
 *
 * TclUtfCount --
 *
 *	Find the number of bytes in the Utf character "ch".

	return 2;
    }
    if (((unsigned)(ch - 0x10000) <= 0xFFFFF)) {
	return 4;
    }
    return 3;
}

/*
 *---------------------------------------------------------------------------
 *
 * Invalid --
 *
 *	Utility routine to report whether /src/ points to the start of an
 *	invald byte sequence that should be rejected. This might be because
 *	it is an overlong encoding, or because it encodes something out of
 *	the proper range. Caller guarantees that src[0] and src[1] are
 *	readable, and
 *
 *	(src[0] >= 0xC0) && (src[0] != 0xC1)
 * 	(src[1] >= 0x80) && (src[1] < 0xC0)
 *	(src[0] < ((TCL_UTF_MAX > 3) ? 0xF5 : 0xF0))
 *
 * Results:
 *	A boolean.
 *---------------------------------------------------------------------------
 */

static const unsigned char bounds[28] = {
    0x80, 0x80,		/* \xC0 accepts \x80 only */
    0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF,
    0x80, 0xBF,		/* (\xC4 - \xDC) -- all sequences valid */
    0xA0, 0xBF,	/* \xE0\x80 through \xE0\x9F are invalid prefixes */
    0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF, /* (\xE4 - \xEC) -- all valid */
    0x90, 0xBF,	/* \xF0\x80 through \xF0\x8F are invalid prefixes */
    0x80, 0x8F  /* \xF4\x90 and higher are invalid prefixes */
};

static int
Invalid(
    unsigned char *src)	/* Points to lead byte of a UTF-8 byte sequence */
{
    unsigned char byte = *src;
    int index;

    if (byte % 0x04) {
	/* Only lead bytes 0xC0, 0xE0, 0xF0, 0xF4 need examination */
	return 0;
    }
    index = (byte - 0xC0) >> 1;
    if (src[1] < bounds[index] || src[1] > bounds[index+1]) {
	/* Out of bounds - report invalid. */
	return 1;
    }
    return 0;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_UniCharToUtf --
 *
 *	Store the given Tcl_UniChar as a sequence of UTF-8 bytes in the
 *	provided buffer. Equivalent to Plan 9 runetochar().

}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_UtfNext --
 *
 *	Given a pointer to some location in a UTF-8 string, Tcl_UtfNext
 *	returns a pointer to the next UTF-8 character in the string.
 *	The caller must not ask for the next character after the last
 *	character in the string if the string is not terminated by a null
 *	character.
 *
 * Results:
 *	The return value is the pointer to the next character in the UTF-8
 *	string.
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

const char *
Tcl_UtfNext(
    const char *src)		/* The current location in the string. */
{

    size_t left = totalBytes[UCHAR(*src)];
    const char *next = src + 1;

    if (((*src) & 0xC0) == 0x80) {
	if ((((*++src) & 0xC0) == 0x80) && (((*++src) & 0xC0) == 0x80)) {
	    ++src;
	}
	return src;
    }



    while (--left) {
	if ((*next & 0xC0) != 0x80) {
	    /*
	     * src points to non-trail byte; We ran out of trail bytes
	     * before the needs of the lead byte were satisfied.
	     * Let the (malformed) lead byte alone be a character
	     */
	    return src + 1;
	}
	next++;
    }
    if (Invalid((unsigned char *)src)) {
	return src + 1;
    }
    return next;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_UtfPrev --
 *

 */

const char *
Tcl_UtfPrev(
    const char *src,		/* A location in a UTF-8 string. */
    const char *start)		/* Pointer to the beginning of the string */
{
    int trailBytesSeen = 0;	/* How many trail bytes have been verified? */
    const char *fallback = src - 1;
				/* If we cannot find a lead byte that might
				 * start a prefix of a valid UTF byte sequence,
				 * we will fallback to a one-byte back step */
    unsigned char *look = (unsigned char *)fallback;
				/* Start search at the fallback position */



    /* Quick boundary case exit. */
    if (fallback <= start) {

	return start;
    }


    do {
	unsigned char byte = look[0];

	if (byte < 0x80) {
	    /*
	     * Single byte character. Either this is a correct previous
	     * character, or it is followed by at least one trail byte
	     * which indicates a malformed sequence. In either case the
	     * correct result is to return the fallback.
	     */
	    return fallback;
	}
	if (byte >= 0xC0) {
	    /* Non-trail byte; May be multibyte lead. */

	    if ((trailBytesSeen == 0)
		/*
		 * We've seen no trailing context to use to check
		 * anything. From what we know, this non-trail byte
		 * is a prefix of a previous character, and accepting
		 * it (the fallback) is correct.
		 */

		    || (trailBytesSeen >= totalBytes[byte])) {
		/*
		 * That is, (1 + trailBytesSeen > needed).
		 * We've examined more bytes than needed to complete
		 * this lead byte. No matter about well-formedness or
		 * validity, the sequence starting with this lead byte
		 * will never include the fallback location, so we must
		 * return the fallback location. See test utf-7.17
		 */
		return fallback;
	    }

	    /*
	     * trailBytesSeen > 0, so we can examine look[1] safely.
	     * Use that capability to screen out overlong sequences.
	     */

	    if (Invalid(look)) {
		/* Reject */
		return fallback;
	    }
	    return (const char *)look;
	}

	/* We saw a trail byte. */
	trailBytesSeen++;

	if ((const char *)look == start) {
	    /*
	     * Do not read before the start of the string
	     *
	     * If we get here, we've examined bytes at every location
	     * >= start and < src and all of them are trail bytes,
	     * including (*start).  We need to return our fallback
	     * and exit this loop before we run past the start of the string.
	     */
	    return fallback;
	}

	/* Continue the search backwards... */
	look--;
    } while (trailBytesSeen < 4);

    /*
     * We've seen TCL_UTF_MAX trail bytes, so we know there will not be a
     * properly formed byte sequence to find, and we can stop looking,
     * accepting the fallback (for TCL_UTF_MAX > 3) or just go back as
     * far as we can.
     */
    return fallback;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_UniCharAtIndex --
 *