threads / patch / 24533

patchhash: Remove useless init_hash()

Subject: [PATCH] hash: Remove useless init_hash()

## tl;dr

7 messages between Jul 27, 2010 and Jul 28, 2010. Diffs are folded; open one to read it.

replies: 6people: 5as markdown or json

Stephen Boyd· Jul 27, 2010, 05:36 UTC · lore
init_hash() is essentially a memset() so just use that.
Signed-off-by: Stephen Boyd <bebarino@gmail.com>
---
 Documentation/technical/api-hash.txt |    4 ----
 diffcore-rename.c                    |    2 +-
 hash.h                               |    7 -------
 3 files changed, 1 insertions(+), 12 deletions(-)
Show changes to 3 files +1 −12

Documentation/technical/api-hash.txt, diffcore-rename.c, hash.h

diff --git a/Documentation/technical/api-hash.txt b/Documentation/technical/api-hash.txt
index e5061e0..7cf64ec 100644
--- a/Documentation/technical/api-hash.txt
+++ b/Documentation/technical/api-hash.txt
@@ -23,10 +23,6 @@ Data Structures
 Functions
 ---------
 
-`init_hash`::
-
-	Initialize the hash table.
-
 `free_hash`::
 
 	Release memory associated with the hash table.
diff --git a/diffcore-rename.c b/diffcore-rename.c
index df41be5..b355520 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -382,7 +382,7 @@ static int find_exact_renames(void)
 	int i;
 	struct hash_table file_table;
 
-	init_hash(&file_table);
+	memset(&file_table, 0, sizeof(file_table));
 	for (i = 0; i < rename_src_nr; i++)
 		insert_file_table(&file_table, -1, i, rename_src[i].one);
 
diff --git a/hash.h b/hash.h
index 69e33a4..418be24 100644
--- a/hash.h
+++ b/hash.h
@@ -33,11 +33,4 @@ extern void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table
 extern int for_each_hash(const struct hash_table *table, int (*fn)(void *));
 extern void free_hash(struct hash_table *table);
 
-static inline void init_hash(struct hash_table *table)
-{
-	table->size = 0;
-	table->nr = 0;
-	table->array = NULL;
-}
-
 #endif

-- 
1.7.2.19.g9a302
Jakub Narebski· Jul 27, 2010, 10:30 UTC · re: Stephen Boyd · lore

Re: [PATCH] hash: Remove useless init_hash()

Stephen Boyd <bebarino@gmail.com> writes:
> init_hash() is essentially a memset() so just use that.
> 
> Signed-off-by: Stephen Boyd <bebarino@gmail.com>
[...]
Encapsulation is good.
Show 10 quoted lines
> diff --git a/diffcore-rename.c b/diffcore-rename.c
> index df41be5..b355520 100644
> --- a/diffcore-rename.c
> +++ b/diffcore-rename.c
> @@ -382,7 +382,7 @@ static int find_exact_renames(void)
>  	int i;
>  	struct hash_table file_table;
>  
> -	init_hash(&file_table);
> +	memset(&file_table, 0, sizeof(file_table));

This is IMHO slightly less readable, and doesn't protect against changes in implementation.

Show 17 quoted lines
>  	for (i = 0; i < rename_src_nr; i++)
>  		insert_file_table(&file_table, -1, i, rename_src[i].one);
>  
> diff --git a/hash.h b/hash.h
> index 69e33a4..418be24 100644
> --- a/hash.h
> +++ b/hash.h
> @@ -33,11 +33,4 @@ extern void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table
>  extern int for_each_hash(const struct hash_table *table, int (*fn)(void *));
>  extern void free_hash(struct hash_table *table);
>  
> -static inline void init_hash(struct hash_table *table)
> -{
> -	table->size = 0;
> -	table->nr = 0;
> -	table->array = NULL;
> -}
*This* could be replaced by memset.
Show 5 quoted lines
> -
>  #endif
> -- 
> 1.7.2.19.g9a302
> 
-- 
Jakub Narebski
Poland
ShadeHawk on #git
Ævar Arnfjörð Bjarmason· Jul 27, 2010, 10:36 UTC · re: Jakub Narebski · lore

Re: [PATCH] hash: Remove useless init_hash()

On Tue, Jul 27, 2010 at 10:30, Jakub Narebski <jnareb@gmail.com> wrote:
CC-ing Linus since he wrote it (per Documentation/SubmittingPatches).
Show 13 quoted lines
> Stephen Boyd <bebarino@gmail.com> writes:
>
>> init_hash() is essentially a memset() so just use that.
>>
>> Signed-off-by: Stephen Boyd <bebarino@gmail.com>
> [...]
>
> Encapsulation is good.
>
> [..]
>
> This is IMHO slightly less readable, and doesn't protect against
> changes in implementation.
Agreed.
Show 19 quoted lines
>>       for (i = 0; i < rename_src_nr; i++)
>>               insert_file_table(&file_table, -1, i, rename_src[i].one);
>>
>> diff --git a/hash.h b/hash.h
>> index 69e33a4..418be24 100644
>> --- a/hash.h
>> +++ b/hash.h
>> @@ -33,11 +33,4 @@ extern void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table
>>  extern int for_each_hash(const struct hash_table *table, int (*fn)(void *));
>>  extern void free_hash(struct hash_table *table);
>>
>> -static inline void init_hash(struct hash_table *table)
>> -{
>> -     table->size = 0;
>> -     table->nr = 0;
>> -     table->array = NULL;
>> -}
>
> *This* could be replaced by memset.

No it couldn't? The second argument to memset is just an int, so setting the memory area to 0 isn't portable to systems where the representation of NULL isn't "0".

(It's early so I may be misremembering my C..)
Jeff King· Jul 27, 2010, 19:49 UTC · re: Ævar Arnfjörð Bjarmason · lore

Re: [PATCH] hash: Remove useless init_hash()

On Tue, Jul 27, 2010 at 10:36:09AM +0000, Ævar Arnfjörð Bjarmason wrote:
Show 14 quoted lines
> >> -static inline void init_hash(struct hash_table *table)
> >> -{
> >> -     table->size = 0;
> >> -     table->nr = 0;
> >> -     table->array = NULL;
> >> -}
> >
> > *This* could be replaced by memset.
> 
> No it couldn't? The second argument to memset is just an int, so
> setting the memory area to 0 isn't portable to systems where the
> representation of NULL isn't "0".
> 
> (It's early so I may be misremembering my C..)

You're remembering your C correctly. It isn't portable, but it is so unlikely on modern machines that we simply don't care (and you will see memsets zero-ing pointers like this all through the git code, so this is certainly not introducing anything new).

That being said, I agree with the comments that removing init_hash actually makes the code _less_ readable. You could just replace these three lines with a memset, but why? It's just code churn.

-Peff
Ævar Arnfjörð Bjarmason· Jul 27, 2010, 19:58 UTC · re: Jeff King · lore

Re: [PATCH] hash: Remove useless init_hash()

On Tue, Jul 27, 2010 at 19:49, Jeff King <peff@peff.net> wrote:
Show 21 quoted lines
> On Tue, Jul 27, 2010 at 10:36:09AM +0000, Ævar Arnfjörð Bjarmason wrote:
>
>> >> -static inline void init_hash(struct hash_table *table)
>> >> -{
>> >> -     table->size = 0;
>> >> -     table->nr = 0;
>> >> -     table->array = NULL;
>> >> -}
>> >
>> > *This* could be replaced by memset.
>>
>> No it couldn't? The second argument to memset is just an int, so
>> setting the memory area to 0 isn't portable to systems where the
>> representation of NULL isn't "0".
>>
>> (It's early so I may be misremembering my C..)
>
> You're remembering your C correctly. It isn't portable, but it is so
> unlikely on modern machines that we simply don't care (and you will see
> memsets zero-ing pointers like this all through the git code, so this is
> certainly not introducing anything new).

Thanks for the confirmation. I was aware that NULL != 0 only occured on long-dead architechtures, but I suspected that some compiler out there would whine if it could statically determine that you were reading in a memzero'd area and using it as NULL. Evidently not, or at least nobody's complained.

> That being said, I agree with the comments that removing init_hash
> actually makes the code _less_ readable. You could just replace these
> three lines with a memset, but why? It's just code churn.
Yeah, and for the record it also missed this part in hash.c:
    void free_hash(struct hash_table *table)
    {
    	free(table->array);
    	table->array = NULL;
    	table->size = 0;
    	table->nr = 0;
    }
Have fun everyone :)
Stephen Boyd· Jul 28, 2010, 07:33 UTC · re: Ævar Arnfjörð Bjarmason · lore

Re: [PATCH] hash: Remove useless init_hash()

  On 07/27/2010 12:58 PM, Ævar Arnfjörð Bjarmason wrote:
Show 15 quoted lines
>
>> That being said, I agree with the comments that removing init_hash
>> actually makes the code _less_ readable. You could just replace these
>> three lines with a memset, but why? It's just code churn.
> Yeah, and for the record it also missed this part in hash.c:
>
>      void free_hash(struct hash_table *table)
>      {
>      	free(table->array);
>      	table->array = NULL;
>      	table->size = 0;
>      	table->nr = 0;
>      }
>
> Have fun everyone :)
Ok, seems like nobody thinks this is a good idea so I'm fine with dropping it. The minimal savings (if at all) doesn't seem worth the code churn. One less patch in the queue ;-)
Linus Torvalds· Jul 27, 2010, 15:55 UTC · re: Stephen Boyd · lore

Re: [PATCH] hash: Remove useless init_hash()

On Mon, Jul 26, 2010 at 10:36 PM, Stephen Boyd <bebarino@gmail.com> wrote:
>
> init_hash() is essentially a memset() so just use that.
I disagree.

Yes, technically right now the initialization just zeroes out all the fields, and memset() does the same. But there is no advantage to using memset(), since init_hash() will create the same or better code, and using init_hash() is way more readable.

Also, it's not at all the case that init_hash() is always going to be a memset(). Imagine a threaded hash-table with a lock associated with it or something. Now, admittedly that's not necessarily something we'd ever do in git, but I still think it's simply a good idea to have a clear "initialize this" routine, rather than depending on the fact that zeroing it out is sufficient.

                    Linus

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