CONST char *
Tcl_UtfPrev(
    CONST char *src,		/* The current location in the string. */
    CONST char *start)		/* Pointer to the beginning of the string, to
				 * avoid going backwards too far. */
{
    static unsigned char maxLead = (TCL_UTF_MAX == 3) ? 0xEF : 0xF7;
    static unsigned char leads[6] = {0xC0, 0xC0, 0xE0, 0xF0, 0xF8, 0xF8};
    int limit,n = 0;
    CONST char *look = src - 1;
    int i, o, known = 0;
    Tcl_UniChar ch;

    if (look <= start) {
    if (src <= start) {
	return start;
    }

    /* simplest case - ascii char */
    limit = ((src - start) < TCL_UTF_MAX) ? (src - start) : TCL_UTF_MAX;

    do {
	unsigned char byte = *((unsigned char *) look);
    if (*((unsigned char *) look) < 0x80) {

	if (byte < 0x80) {
	    /* An 7-bit ASCII byte followed by n trail bytes indicates the
	     * last trail byte was the answer. */
	    return src - 1;
	}
	if (byte > maxLead) {
	return look;
    }
    /* navigate up to max return value of Tcl_UtfToUniChar */
    for (i = 1; i <= 4; i++) {
	if (look < start) {
	    /* A byte value too large to be a valid lead byte indicates the
	     * last trail byte was the answer */
	   return src - 1;
	    look = start;
	    break;
	}
	if (byte >= leads[n++]) {
	if (*((unsigned char *) look) < 0x80) {
	    /* A lead byte that can accept up to n trail bytes becomes
	     * the answer. */
	    return look;
	    /* traversing back reaches ascii - either known mark points to char,
	     * or unexpected case with invalid utf-8 or unsupported surrogate 
	     * starting from next char, so goto next char and stop search: */
	    look++;
	    break;
	}
	o = Tcl_UtfToUniChar(look, &ch);
	/* if we are reached start of some char, mark as known and try further */
	if (byte >= 0xC0) {
	if (o >= i) {
	    /* A lead byte that cannot accept n trail bytes indicates
	     * the last trail byte the answer. */
	    return src - 1;
	    known = i;
	}
	look--;

    }
	/* We saw a trail byte; keep scanning. */
	look--;
    /* use best (marked as known) char position, or current found if unknown: */
    if (known) {
	look = src - known;
    } while (n < limit);

    }
    /* We saw nothing but trail bytes until the limit was reached.
     * Indicates the last trail byte is the answer. */
    return src - 1;
    return look;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_UniCharAtIndex --
 *