str_foldcase(
    char_u	*str,
    int		orglen,
    char_u	*buf,
    int		buflen)
{
    garray_T	ga;
    int		i;
    int		len = orglen;

#define GA_CHAR(i)  ((char_u *)ga.ga_data)[i]
#define GA_PTR(i)   ((char_u *)ga.ga_data + (i))
#define STR_CHAR(i)  (buf == NULL ? GA_CHAR(i) : buf[i])
#define STR_PTR(i)   (buf == NULL ? GA_PTR(i) : buf + (i))

    // Copy "str" into "buf" or allocated memory, unmodified.
    if (buf == NULL)
    {
	ga_init2(&ga, 1, 10);
	if (ga_grow(&ga, len + 1) == FAIL)
	    return NULL;
	mch_memmove(ga.ga_data, str, (size_t)len);
	ga.ga_len = len;
    }
    else
    {
	if (len >= buflen)	    // Ugly!
	    len = buflen - 1;
	mch_memmove(buf, str, (size_t)len);
    }
    if (buf == NULL)
	GA_CHAR(len) = NUL;
    else
	buf[len] = NUL;

    // Make each character lower case.
    i = 0;
    while (STR_CHAR(i) != NUL)
    {
	if (enc_utf8 || (has_mbyte && MB_BYTE2LEN(STR_CHAR(i)) > 1))
	{
	    if (enc_utf8)
	    {
		int	c = utf_ptr2char(STR_PTR(i));
		int	olen = utf_ptr2len(STR_PTR(i));
		int	lc = utf_tolower(c);

		// Only replace the character when it is not an invalid
		// sequence (ASCII character or more than one byte) and
		// utf_tolower() doesn't return the original character.
		if ((c < 0x80 || olen > 1) && c != lc)
		{
		    int	    nlen = utf_char2len(lc);

		    // If the byte length changes need to shift the following
		    // characters forward or backward.
		    if (olen != nlen)
		    {
			if (nlen > olen)
			{
			    if (buf == NULL
				    ? ga_grow(&ga, nlen - olen + 1) == FAIL
				    : len + nlen - olen >= buflen)
			    {
				// out of memory, keep old char
				lc = c;
				nlen = olen;
			    }
			}
			if (olen != nlen)
			{
			    if (buf == NULL)
			    {
				STRMOVE(GA_PTR(i) + nlen, GA_PTR(i) + olen);
				ga.ga_len += nlen - olen;
			    }
			    else
			    {
				STRMOVE(buf + i + nlen, buf + i + olen);
				len += nlen - olen;
			    }
			}
		    }
		    (void)utf_char2bytes(lc, STR_PTR(i));
		}
	    }
	    // skip to next multi-byte char
	    i += (*mb_ptr2len)(STR_PTR(i));
	}
	else
	{
	    if (buf == NULL)
		GA_CHAR(i) = TOLOWER_LOC(GA_CHAR(i));
	    else
		buf[i] = TOLOWER_LOC(buf[i]);
	    ++i;
	}
    }

    if (buf == NULL)
	return (char_u *)ga.ga_data;
    return buf;
}