StringScanner#scan_base16_integer

static VALUE
strscan_scan_base16_integer(VALUE self)
{
    char *ptr;
    long len = 0;
    struct strscanner *p;

    GET_SCANNER(self, p);
    CLEAR_MATCH_STATUS(p);

    strscan_must_ascii_compat(p->str);

    ptr = CURPTR(p);

    long remaining_len = S_RESTLEN(p);

    if (remaining_len <= 0) {
        return Qnil;
    }

    if (ptr[len] == '-' || ptr[len] == '+') {
        len++;
    }

    if ((remaining_len >= (len + 2)) && ptr[len] == '0' && ptr[len + 1] == 'x') {
        len += 2;
    }

    if (len >= remaining_len || !rb_isxdigit(ptr[len])) {
        return Qnil;
    }

    MATCHED(p);
    p->prev = p->curr;

    while (len < remaining_len && rb_isxdigit(ptr[len])) {
        len++;
    }

    return strscan_parse_integer(p, 16, len);
}