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SubjectRe: [RFC 1/4] hashtable: introduce a small and naive hashtable
On 08/02/2012 06:15 PM, Josh Triplett wrote:
> On Thu, Aug 02, 2012 at 03:04:19PM +0200, Sasha Levin wrote:
>> On 08/02/2012 01:23 PM, Sasha Levin wrote:
>>>> #define DEFINE_HASH_TABLE(name, length) struct hash_table name = { .count = length, .buckets = { [0 ... (length - 1)] = HLIST_HEAD_INIT } }
>>> The limitation of this approach is that the struct hash_table variable must be 'static', which is a bit limiting - see for example the use of hashtable in 'struct user_namespace'.
>>>
>>
>> What if we just use two possible decelerations? One of static structs and one for regular ones.
>>
>> struct hash_table {
>> size_t bits;
>> struct hlist_head buckets[];
>> };
>>
>> #define DEFINE_HASHTABLE(name, bits) \
>> union { \
>> struct hash_table name; \
>> struct { \
>> size_t bits; \
>
> This shouldn't use "bits", since it'll get expanded to the macro
> argument.
>
>> struct hlist_head buckets[1 << bits]; \
>> } __name; \
>
> __##name
>
>> }
>>
>> #define DEFINE_STATIC_HASHTABLE(name, bit) \
>> static struct hash_table name = { .bits = bit, \
>> .buckets = { [0 ... (bit - 1)] = HLIST_HEAD_INIT } }
>
> You probably wanted to change that to [0 ... ((1 << bit) - 1)] , to
> match DEFINE_HASHTABLE.

I wrote it by hand and didn't compile test, will fix all of those.

> Since your definition of DEFINE_HASHTABLE would also work fine when used
> statically, why not just always use that?
>
> #define DEFINE_STATIC_HASHTABLE(name, bits) static DEFINE_HASHTABLE(name, bits) = { .name.bits = bits }

It will get defined fine, but it will be awkward to use. We'd need to pass anonymous union to all the functions that handle this hashtable, which isn't pretty.



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