static VALUE
lazy_take_func(VALUE val, VALUE args, int argc, VALUE *argv)
{
    long remain;
    VALUE memo = rb_attr_get(argv[0], id_memo);
    if (NIL_P(memo)) {
	memo = args;
    }

    rb_funcall2(argv[0], id_yield, argc - 1, argv + 1);
    if ((remain = NUM2LONG(memo)-1) == 0) {
	return Qundef;
    }
    else {
	rb_ivar_set(argv[0], id_memo, LONG2NUM(remain));
	return Qnil;
    }
}

/*
 * A class for calculating message digests using the SHA-1 Secure Hash
 * Algorithm by NIST (the US' National Institute of Standards and
 * Technology), described in FIPS PUB 180-1.
 */
void
Init_sha1()
{
    VALUE mDigest, cDigest_Base, cDigest_SHA1;

    rb_require("digest");

#if 0
    mDigest = rb_define_module("Digest"); /* let rdoc know */
#endif
    mDigest = rb_path2class("Digest");
    cDigest_Base = rb_path2class("Digest::Base");

    cDigest_SHA1 = rb_define_class_under(mDigest, "SHA1", cDigest_Base);

    rb_ivar_set(cDigest_SHA1, rb_intern("metadata"),
      Data_Wrap_Struct(rb_cObject, 0, 0, (void *)&sha1));
}

static VALUE
cr_s_wrap (VALUE self, VALUE pointer)
{
  VALUE result;
  VALUE rb_cr;
  cairo_t *cr;

  if (NIL_P (rb_cairo__cFFIPointer))
    {
      rb_raise (rb_eNotImpError,
                "%s: FFI::Pointer is required",
                rb_id2name (rb_frame_this_func ()));
    }

  if (!RTEST (rb_obj_is_kind_of (pointer, rb_cairo__cFFIPointer)))
    {
      rb_raise (rb_eArgError,
                "must be FFI::Pointer: %s",
                rb_cairo__inspect (pointer));
    }

  {
    VALUE rb_cr_address;
    rb_cr_address = rb_funcall (pointer, rb_intern ("address"), 0);
    cr = NUM2PTR (rb_cr_address);
    cr_check_status (cr);
  }

  rb_cr = rb_obj_alloc (self);
  cairo_reference (cr);
  DATA_PTR (rb_cr) = cr;
  rb_ivar_set (rb_cr, cr_id_surface, Qnil);

  if (rb_block_given_p ())
    {
      result = rb_ensure (rb_yield, rb_cr, cr_destroy_with_destroy_check, rb_cr);
    }
  else
    {
      result = rb_cr;
    }

  return result;
}

/* call-seq:
 *    XML::Reader.io(io) -> XML::Reader
 *    XML::Reader.io(io, :encoding => XML::Encoding::UTF_8,
 *                       :options => XML::Parser::Options::NOENT) -> XML::Parser
 *
 * Creates a new reader by parsing the specified io object.
 *
 * You may provide an optional hash table to control how the
 * parsing is performed.  Valid options are:
 *
 *  base_uri - The base url for the parsed document.
 *  encoding - The document encoding, defaults to nil. Valid values
 *             are the encoding constants defined on XML::Encoding.
 *  options - Controls the execution of the parser, defaults to 0.
 *            Valid values are the constants defined on
 *            XML::Parser::Options.  Mutliple options can be combined
 *            by using Bitwise OR (|). 
 */
static VALUE rxml_reader_io(int argc, VALUE *argv, VALUE klass)
{
  xmlTextReaderPtr xreader;
  VALUE result;
  VALUE io;
  VALUE options;
  char *xbaseurl = NULL;
  const char *xencoding = NULL;
  int xoptions = 0;

  rb_scan_args(argc, argv, "11", &io, &options);

  if (!NIL_P(options))
  {
    VALUE baseurl = Qnil;
    VALUE encoding = Qnil;
    VALUE parserOptions = Qnil;

    Check_Type(options, T_HASH);

    baseurl = rb_hash_aref(options, BASE_URI_SYMBOL);
    xbaseurl = NIL_P(baseurl) ? NULL : StringValueCStr(baseurl);

    encoding = rb_hash_aref(options, ENCODING_SYMBOL);
    xencoding = NIL_P(encoding) ? NULL : xmlGetCharEncodingName(NUM2INT(encoding));

    parserOptions = rb_hash_aref(options, OPTIONS_SYMBOL);
    xoptions = NIL_P(parserOptions) ? 0 : NUM2INT(parserOptions);
  }
  
  xreader = xmlReaderForIO((xmlInputReadCallback) rxml_read_callback, NULL,
                           (void *) io, 
                           xbaseurl, xencoding, xoptions);

  if (xreader == NULL)
    rxml_raise(&xmlLastError);

  result = rxml_reader_wrap(xreader);

  /* Attach io object to parser so it won't get freed.*/
  rb_ivar_set(result, IO_ATTR, io);

  return result;
}

static VALUE
rbosa_element_make (VALUE klass, AEDesc *desc, VALUE app)
{
    AEDesc *    newDesc;
    VALUE       new_klass, obj;

    newDesc = (AEDesc *)malloc (sizeof (AEDesc));
    if (newDesc == NULL)
        rb_fatal ("cannot allocate memory");
    memcpy (newDesc, desc, sizeof (AEDesc));
    new_klass = Qnil;

    /* Let's replace the klass here according to the type of the descriptor,
     * if the basic class OSA::Element was given.
     */
    if (klass == cOSAElement) {
        if (newDesc->descriptorType == 'list') {
            klass = cOSAElementList;
        }
        else if (newDesc->descriptorType == 'reco') {
            klass = cOSAElementRecord;
        }
        else if (newDesc->descriptorType == 'type') {
            new_klass = __rbosa_class_from_desc_data (app, *newDesc);
        }
        else if (newDesc->descriptorType == 'obj ' && !NIL_P (app)) {
            AEDesc  res;
            OSErr   err;

            if ((err = AEGetParamDesc ((AppleEvent *)newDesc, 'want', '****', &res)) == noErr)
                new_klass = __rbosa_class_from_desc_data (app, res);
        }
    }

    if (!NIL_P (new_klass))
        klass = new_klass; 
    
    obj = Data_Wrap_Struct (klass, NULL, rbosa_element_free, newDesc);

    rb_ivar_set (obj, sApp, NIL_P (app) ? obj : app);

    return obj;
}

/*
 * Create an empty media list.
 *
 * @param [VLC::Core] core the core instance
 * @raise [ArgumentError] Invalid or unsupported arguments
 * @todo fixme
 */
static VALUE
rg_initialize(int argc, VALUE *argv, VALUE self)
{
    VALUE core;
    libvlc_media_list_t *instance;

    rb_scan_args(argc, argv, "01", &core);
    if (NIL_P(core))
        core = rb_funcall(GTYPE2CLASS(VLC_TYPE_CORE), rb_intern("new"), 0);

    instance = libvlc_media_list_new(RVAL2VLCCORE(core));
    if (!instance)
        rb_raise(rb_eArgError, "Invalid arguments.");
    rb_ivar_set(self, id_core, core);

    G_INITIALIZE(self, instance);
    vlc_media_list_free(instance);
    return Qnil;
}

VALUE Message_alloc(VALUE klass) {
  VALUE descriptor = rb_ivar_get(klass, descriptor_instancevar_interned);
  Descriptor* desc = ruby_to_Descriptor(descriptor);
  MessageHeader* msg = (MessageHeader*)ALLOC_N(
      uint8_t, sizeof(MessageHeader) + desc->layout->size);
  VALUE ret;

  memset(Message_data(msg), 0, desc->layout->size);

  // We wrap first so that everything in the message object is GC-rooted in case
  // a collection happens during object creation in layout_init().
  ret = TypedData_Wrap_Struct(klass, &Message_type, msg);
  msg->descriptor = desc;
  rb_ivar_set(ret, descriptor_instancevar_interned, descriptor);

  layout_init(desc->layout, Message_data(msg));

  return ret;
}

static VALUE
cr_get_target (VALUE self)
{
  cairo_surface_t *surface;
  VALUE rb_surface = Qnil;

  surface = cairo_get_target (_SELF);
  rb_cairo_check_status (cairo_surface_status (surface));

  if (RTEST (rb_ivar_defined (self, cr_id_surface)))
      rb_surface = rb_ivar_get (self, cr_id_surface);
  if (NIL_P (rb_surface) || RVAL2CRSURFACE (rb_surface) != surface)
    {
      rb_surface = CRSURFACE2RVAL (surface);
      rb_ivar_set (self, cr_id_surface, rb_surface);
    }

  return rb_surface;
}

void
rbgtk_initialize_gtkobject(VALUE obj, GtkObject *gtkobj)
{
    gtkobj = g_object_ref(gtkobj);
    gtk_object_sink(gtkobj);
    G_INITIALIZE(obj, gtkobj);

    if (GTK_IS_WINDOW(gtkobj) || GTK_IS_MENU_SHELL(gtkobj)) {
        VALUE klass;
        klass = rb_obj_class(obj);
        if (rb_ivar_defined(klass, id__windows__) == Qfalse) {
            rb_ivar_set(klass, id__windows__, rb_hash_new());
        }
        rb_hash_aset(rb_ivar_get(klass, id__windows__), obj, Qnil);
        g_signal_connect_after(gtkobj, "destroy",
                               G_CALLBACK(remove_from_windows),
                               (gpointer)obj);
    }
}

/* Synchronize around a reentrant selector lock */
static VALUE NIO_Selector_synchronize(VALUE self, VALUE (*func)(VALUE *args), VALUE *args)
{
    VALUE current_thread, lock_holder, lock;

    current_thread = rb_thread_current();
    lock_holder = rb_ivar_get(self, rb_intern("lock_holder"));

    if(lock_holder != current_thread) {
        lock = rb_ivar_get(self, rb_intern("lock"));
        rb_funcall(lock, rb_intern("lock"), 0, 0);
        rb_ivar_set(self, rb_intern("lock_holder"), current_thread);

        /* We've acquired the lock, so ensure we unlock it */
        return rb_ensure(func, (VALUE)args, NIO_Selector_unlock, self);
    } else {
        /* We already hold the selector lock, so no need to unlock it */
        return func(args);
    }
}

static VALUE
cr_initialize (VALUE self, VALUE target)
{
  cairo_t *cr;
  VALUE result = Qnil;

  cr = cairo_create (RVAL2CRSURFACE (target));
  cr_check_status (cr);
  rb_ivar_set (self, cr_id_surface, target);
  if (rb_ivar_defined (target, rb_cairo__io_id_output))
    cr_set_user_data (cr,
                      &cr_object_holder_key,
                      cr_object_holder_new (self),
                      cr_object_holder_free);
  DATA_PTR (self) = cr;
  if (rb_block_given_p ())
    result = rb_ensure (rb_yield, self, cr_destroy_with_destroy_check, self);
  return result;
}

static VALUE
lazy_zip_arrays_func(VALUE val, VALUE arrays, int argc, VALUE *argv)
{
    VALUE yielder, ary, memo;
    long i, count;

    yielder = argv[0];
    memo = rb_attr_get(yielder, id_memo);
    count = NIL_P(memo) ? 0 : NUM2LONG(memo);

    ary = rb_ary_new2(RARRAY_LEN(arrays) + 1);
    rb_ary_push(ary, argv[1]);
    for (i = 0; i < RARRAY_LEN(arrays); i++) {
	rb_ary_push(ary, rb_ary_entry(RARRAY_AREF(arrays, i), count));
    }
    rb_funcall(yielder, id_yield, 1, ary);
    rb_ivar_set(yielder, id_memo, LONG2NUM(++count));
    return Qnil;
}

static VALUE
cr_text_to_glyphs_data_initialize (VALUE self,
                                   VALUE need_glyphs, VALUE need_clusters,
                                   VALUE need_cluster_flags)
{
  rb_ivar_set (self, cr_id_at_glyphs, Qnil);
  rb_ivar_set (self, cr_id_at_clusters, Qnil);
  rb_ivar_set (self, cr_id_at_cluster_flags, INT2NUM (0));
  rb_ivar_set (self, cr_id_at_need_glyphs, need_glyphs);
  rb_ivar_set (self, cr_id_at_need_clusters, need_clusters);
  rb_ivar_set (self, cr_id_at_need_cluster_flags, need_cluster_flags);

  return Qnil;
}

/*
 * @return [Array<RPM::Package>] Packages defined in the spec file
 */
VALUE
rpm_spec_get_packages(VALUE spec)
{
	VALUE pkg = rb_ivar_get(spec, id_pkg);

	if (NIL_P(pkg)) {
		Package p = RPM_SPEC(spec)->packages;

		pkg = rb_ary_new();
		while (p != NULL) {
			if (p->fileList)
				rb_ary_push(pkg, rpm_package_new_from_header(p->header));
			p = p->next;
		}

		rb_ivar_set(spec, id_pkg, pkg);
	}

	return pkg;
}

static VALUE
rg_initialize(VALUE self, VALUE type)
{
    GType gtype;

    if (RVAL2CBOOL(rb_obj_is_kind_of(type, rb_cInteger))) {
        gtype = NUM2ULONG(type);
        if (!g_type_name(gtype))
            gtype = G_TYPE_INVALID;
    } else {
        gtype = g_type_from_name(StringValuePtr(type));
    }

    if (G_TYPE_INVALID == gtype)
        rb_raise(rb_eArgError, "invalid GType");

    rb_ivar_set(self, id_gtype, ULONG2NUM(gtype));

    return Qnil;
}

VALUE
rbffi_Function_ForProc(VALUE rbFunctionInfo, VALUE proc)
{
    VALUE callback;
    VALUE cbTable = RTEST(rb_ivar_defined(proc, id_cbtable)) ? rb_ivar_get(proc, id_cbtable) : Qnil;

    if (cbTable == Qnil) {
        cbTable = rb_hash_new();
        rb_ivar_set(proc, id_cbtable, cbTable);
    }

    callback = rb_hash_aref(cbTable, rbFunctionInfo);
    if (callback != Qnil) {
        return callback;
    }

    callback = rbffi_Function_NewInstance(rbFunctionInfo, proc);
    rb_hash_aset(cbTable, rbFunctionInfo, callback);
    return callback;
}

static VALUE
rb_rsvg_handle_close(VALUE self)
{
    gboolean result;
    GError *error = NULL;

    if (RVAL2CBOOL(rb_ivar_get(self, id_closed))) {
        return Qnil;
    }

    result = rsvg_handle_close(_SELF(self), &error);

    if (result) {
        rb_ivar_set(self, id_closed, Qtrue);
    } else {
        RAISE_GERROR(error);
    }

    return CBOOL2RVAL(result);
}

static void
raise_argument_error(rb_thread_t *th, const rb_iseq_t *iseq, const VALUE exc)
{
    VALUE at;

    if (iseq) {
	vm_push_frame(th, iseq, VM_FRAME_MAGIC_DUMMY, Qnil /* self */,
		      VM_ENVVAL_BLOCK_PTR(0) /* specval*/, Qfalse /* me or cref */,
		      iseq->body->iseq_encoded, th->cfp->sp, 1 /* local_size (cref/me) */, 0 /* stack_max */);
	at = rb_vm_backtrace_object();
	vm_pop_frame(th);
    }
    else {
	at = rb_vm_backtrace_object();
    }

    rb_ivar_set(exc, idBt_locations, at);
    rb_exc_set_backtrace(exc, at);
    rb_exc_raise(exc);
}

static VALUE Sprite_initialize(int argc, VALUE *argv, VALUE self) {
  VALUE sprites = rb_ivar_get(mGraphics, rb_intern("@sprites"));
  VALUE src_rect = rb_class_new_instance(0, NULL, cRect);
  Sprite *sprite = EXT_SPRITE(self);

  rb_ary_push(sprites, self);
  old_call(self, rb_intern("initialize"), argc, argv);

  src_rect = old_call(self, rb_intern("src_rect"), 0, NULL); /* TODO */
  rb_ivar_set(self, rb_intern("@src_rect"), src_rect);
  Rect__add_ref(src_rect, self);
  sprite->src_rect = src_rect;

  sprite->x = sprite->y = 0;
  sprite->ox = sprite->oy = 0;
  sprite->disposed = 0;
  sprite->visible = 1;

  return self;
}

static VALUE rb_eu_escape_html_as_html_safe(VALUE self, VALUE str)
{
	VALUE result;
	int secure = g_html_secure;
	gh_buf buf = GH_BUF_INIT;

	Check_Type(str, T_STRING);
	check_utf8_encoding(str);

	if (houdini_escape_html0(&buf, (const uint8_t *)RSTRING_PTR(str), RSTRING_LEN(str), secure)) {
		result = new_html_safe_string(buf.ptr, buf.size);
		gh_buf_free(&buf);
	} else {
		result = new_html_safe_string(RSTRING_PTR(str), RSTRING_LEN(str));
	}

	rb_ivar_set(result, ID_at_html_safe, Qtrue);

	return result;
}