/*
* Copyright © 2008 Ryan Lortie
* Copyright © 2010 Codethink Limited
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*
* Author: Ryan Lortie <desrt@desrt.ca>
*/
#ifndef __G_VARIANT_TYPE_INFO_H__
#define __G_VARIANT_TYPE_INFO_H__
#include <glib/gvarianttype.h>
#define G_VARIANT_TYPE_INFO_CHAR_MAYBE 'm'
#define G_VARIANT_TYPE_INFO_CHAR_ARRAY 'a'
#define G_VARIANT_TYPE_INFO_CHAR_TUPLE '('
#define G_VARIANT_TYPE_INFO_CHAR_DICT_ENTRY '{'
#define G_VARIANT_TYPE_INFO_CHAR_VARIANT 'v'
#define g_variant_type_info_get_type_char(info) \
(g_variant_type_info_get_type_string(info)[0])
typedef struct _GVariantTypeInfo GVariantTypeInfo;
/* < private >
* GVariantMemberInfo:
*
* This structure describes how to construct a GVariant instance
* corresponding to a given child of a tuple or dictionary entry in a
* very short constant time. It contains the typeinfo of the child,
* along with 4 constants that allow the bounds of the child's
* serialised data within the container's serialised data to be found
* very efficiently.
*
* Since dictionary entries are serialised as if they were tuples of 2
* items, the term "tuple" will be used here in the general sense to
* refer to tuples and dictionary entries.
*
* BACKGROUND:
* The serialised data for a tuple contains an array of "offsets" at
* the end. There is one "offset" in this array for each
* variable-sized item in the tuple (except for the last one). The
* offset points to the end point of that item's serialised data. The
* procedure for finding the start point is described below. An
* offset is not needed for the last item because the end point of the
* last item is merely the end point of the container itself (after
* the offsets array has been accounted for). An offset is not needed
* for fixed-sized items (like integers) because, due to their fixed
* size, the end point is a constant addition to the start point.
*
* It is clear that the starting point of a given item in the tuple is
* determined by the items that preceed it in the tuple. Logically,
* the start point of a particular item in a given type of tuple can
* be determined entirely by the end point of the nearest
* variable-sized item that came before it (or from the start of the
* container itself in case there is no preceeding variable-sized
* item). In the case of "(isis)" for example, in order to find out
* the start point of the last string, one must start at the end point
* of the first string, align to 4 (for the integer's alignment) and
* then add 4 (for storing the integer). That's the point where the
* string starts (since no special alignment is required for strings).
*
* Of course, this process requires iterating over the types in the
* tuple up to the item of interest. As it turns out, it is possible
* to determine 3 constants 'a', 'b', and 'c' for each item in the
* tuple, such that, given the ending offset of the nearest previous
* variable-sized item (prev_end), a very simple calculation can be
* performed to determine the start of the item of interest.
*
* The constants in this structure are used as follows:
*
* First, among the array of offets contained in the tuple, 'i' is the
* index of the offset that refers to the end of the variable-sized item
* preceeding the item of interest. If no variable-sized items preceed
* this item, then 'i' will be -1.
*
* Let 'prev_end' be the end offset of the previous item (or 0 in the
* case that there was no such item). The start address of this item
* can then be calculate using 'a', 'b', and 'c':
*
* item_start = ((prev_end + a) & b) | c;
*
* For details about how 'a', 'b' and 'c' are calculated, see the
* comments at the point of the implementation in gvariantypeinfo.c.
*
* The end address of the item is then determined in one of three ways,
* according to the 'end_type' field.
*
* - FIXED: For fixed sized items, the end address is equal to the
* start address plus the fixed size.
*
* - LAST: For the last variable sized item in the tuple, the end
* address is equal to the end address of the tuple, minus the size
* of the offset array.
*
* - OFFSET: For other variable sized items, the next index past 'i'
* (ie: 'i + 1') must be consulted to find the end of this item.
*/
typedef struct
{
GVariantTypeInfo *type_info;
gsize i, a;
gint8 b, c;
guint8 ending_type;
} GVariantMemberInfo;
#define G_VARIANT_MEMBER_ENDING_FIXED 0
#define G_VARIANT_MEMBER_ENDING_LAST 1
#define G_VARIANT_MEMBER_ENDING_OFFSET 2
/* query */
const gchar * g_variant_type_info_get_type_string (GVariantTypeInfo *typeinfo);
void g_variant_type_info_query (GVariantTypeInfo *typeinfo,
guint *alignment,
gsize *size);
/* array */
GVariantTypeInfo * g_variant_type_info_element (GVariantTypeInfo *typeinfo);
void g_variant_type_info_query_element (GVariantTypeInfo *typeinfo,
guint *alignment,
gsize *size);
/* structure */
gsize g_variant_type_info_n_members (GVariantTypeInfo *typeinfo);
const GVariantMemberInfo * g_variant_type_info_member_info (GVariantTypeInfo *typeinfo,
gsize index);
/* new/ref/unref */
GVariantTypeInfo * g_variant_type_info_get (const GVariantType *type);
GVariantTypeInfo * g_variant_type_info_ref (GVariantTypeInfo *typeinfo);
void g_variant_type_info_unref (GVariantTypeInfo *typeinfo);
void g_variant_type_info_assert_no_infos (void);
#endif /* __G_VARIANT_TYPE_INFO_H__ */
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