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OFFSETOF_VAR macro to simplify hashmap iterators

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While we cannot rely on a `__typeof__' operator being portable
to use with `offsetof'; we can calculate the pointer offset
using an existing pointer and the address of a member using
pointer arithmetic for compilers without `__typeof__'.

This allows us to simplify usage of hashmap iterator macros
by not having to specify a type when a pointer of that type
is already given.

In the future, list iterator macros (e.g. list_for_each_entry)
may also be implemented using OFFSETOF_VAR to save hackers the
trouble of using container_of/list_entry macros and without
relying on non-portable `__typeof__'.

v3: use `__typeof__' to avoid clang warnings

Signed-off-by: Eric Wong <e@80x24.org>
Reviewed-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Eric Wong
2019-10-06 23:30:41 +00:00
committed by Junio C Hamano
parent c8e424c9c9
commit 23dee69f53
15 changed files with 56 additions and 45 deletions
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44
hashmap.h
View File

@ -408,16 +408,32 @@ static inline struct hashmap_entry *hashmap_iter_first(struct hashmap *map,
return hashmap_iter_next(iter);
}
#define hashmap_iter_next_entry(iter, type, member) \
container_of_or_null(hashmap_iter_next(iter), type, member)
/*
* returns the first entry in @map using @iter, where the entry is of
* @type (e.g. "struct foo") and @member is the name of the
* "struct hashmap_entry" in @type
*/
#define hashmap_iter_first_entry(map, iter, type, member) \
container_of_or_null(hashmap_iter_first(map, iter), type, member)
#define hashmap_for_each_entry(map, iter, var, type, member) \
for (var = hashmap_iter_first_entry(map, iter, type, member); \
/* internal macro for hashmap_for_each_entry */
#define hashmap_iter_next_entry_offset(iter, offset) \
container_of_or_null_offset(hashmap_iter_next(iter), offset)
/* internal macro for hashmap_for_each_entry */
#define hashmap_iter_first_entry_offset(map, iter, offset) \
container_of_or_null_offset(hashmap_iter_first(map, iter), offset)
/*
* iterate through @map using @iter, @var is a pointer to a type
* containing a @member which is a "struct hashmap_entry"
*/
#define hashmap_for_each_entry(map, iter, var, member) \
for (var = hashmap_iter_first_entry_offset(map, iter, \
OFFSETOF_VAR(var, member)); \
var; \
var = hashmap_iter_next_entry(iter, type, member))
var = hashmap_iter_next_entry_offset(iter, \
OFFSETOF_VAR(var, member)))
/*
* returns a @pointer of @type matching @keyvar, or NULL if nothing found.
@ -432,22 +448,22 @@ static inline struct hashmap_entry *hashmap_iter_first(struct hashmap *map,
container_of_or_null(hashmap_get_from_hash(map, hash, keydata), \
type, member)
/*
* returns the next equal @type pointer to @var, or NULL if not found.
* @var is a pointer of @type
* @member is the name of the "struct hashmap_entry" field in @type
* returns the next equal pointer to @var, or NULL if not found.
* @var is a pointer of any type containing "struct hashmap_entry"
* @member is the name of the "struct hashmap_entry" field
*/
#define hashmap_get_next_entry(map, var, type, member) \
container_of_or_null(hashmap_get_next(map, &(var)->member), \
type, member)
#define hashmap_get_next_entry(map, var, member) \
container_of_or_null_offset(hashmap_get_next(map, &(var)->member), \
OFFSETOF_VAR(var, member))
/*
* iterate @map starting from @var, where @var is a pointer of @type
* and @member is the name of the "struct hashmap_entry" field in @type
*/
#define hashmap_for_each_entry_from(map, var, type, member) \
#define hashmap_for_each_entry_from(map, var, member) \
for (; \
var; \
var = hashmap_get_next_entry(map, var, type, member))
var = hashmap_get_next_entry(map, var, member))
/*
* Disable item counting and automatic rehashing when adding/removing items.