file.c:785
static VALUE
check3rdbyte(fname, mode)
    VALUE fname;
    int mode;
{
    struct stat st;

    SafeStringValue(fname);
    if (stat(StringValueCStr(fname), &st) < 0) return Qfalse;
    if (st.st_mode & mode) return Qtrue;
    return Qfalse;
}
