int asn1_valid_host(const ASN1_STRING *host)
{
    int hostlen = host->length;
    const unsigned char *hostptr = host->data;
    int type = host->type;
    int i;
    signed char width = -1;
    unsigned short chflags = 0, prevchflags;

    if (type > 0 && type < 31)
        width = tag2nbyte[type];
    if (width == -1 || hostlen == 0)
        return 0;
    /* Treat UTF8String as width 1 as any MSB set is invalid */
    if (width == 0)
        width = 1;
    for (i = 0 ; i < hostlen; i+= width) {
        prevchflags = chflags;
        /* Value must be <= 0x7F: check upper bytes are all zeroes */
        if (width == 4) {
            if (*hostptr++ != 0 || *hostptr++ != 0 || *hostptr++ != 0)
                return 0;
        } else if (width == 2) {
            if (*hostptr++ != 0)
                return 0;
        }
        if (*hostptr > 0x7f)
            return 0;
        chflags = char_type[*hostptr++];
        if (!(chflags & (CHARTYPE_HOST_ANY | CHARTYPE_HOST_WILD))) {
            /* Nothing else allowed at start or end of string */
            if (i == 0 || i == hostlen - 1)
                return 0;
            /* Otherwise invalid if not dot or hyphen */
            if (!(chflags & (CHARTYPE_HOST_DOT | CHARTYPE_HOST_HYPHEN)))
                return 0;
            /*
             * If previous is dot or hyphen then illegal unless both
             * are hyphens: as .- -. .. are all illegal
             */
            if (prevchflags & (CHARTYPE_HOST_DOT | CHARTYPE_HOST_HYPHEN)
                && ((prevchflags & CHARTYPE_HOST_DOT)
                    || (chflags & CHARTYPE_HOST_DOT)))
                return 0;
        }
    }
    return 1;
}