lkml.org 
[lkml]   [2012]   [Aug]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 1/4] hashtable: introduce a small and naive hashtable
On Thu, Aug 02, 2012 at 12:00:33PM +0200, Sasha Levin wrote:
> On 08/02/2012 12:45 AM, Tejun Heo wrote:
> > On Thu, Aug 02, 2012 at 12:41:56AM +0200, Sasha Levin wrote:
> >> How would your DEFINE_HASHTABLE look like if we got for the simple
> >> 'struct hash_table' approach?
> >
> > I think defining a different enclosing anonymous struct which the
> > requested number of array entries and then aliasing the actual
> > hash_table to that symbol should work. It's rather horrible and I'm
> > not sure it's worth the trouble.
>
> I agree that this is probably not worth the trouble.
>
> At the moment I see two alternatives:
>
> 1. Dynamically allocate the hash buckets.
>
> 2. Use the first bucket to store size. Something like the follows:
>
> #define HASH_TABLE(name, bits) \
> struct hlist_head name[1 << bits + 1];
>
> #define HASH_TABLE_INIT (bits) ({name[0].next = bits});
>
> And then have hash_{add,get} just skip the first bucket.
>
>
> While it's not a pretty hack, I don't see a nice way to avoid having to dynamically allocate buckets for all cases.

What about using a C99 flexible array member? Kernel style prohibits
variable-length arrays, but I don't think the same rationale applies to
flexible array members.

struct hash_table {
size_t count;
struct hlist_head buckets[];
};

#define DEFINE_HASH_TABLE(name, length) struct hash_table name = { .count = length, .buckets = { [0 ... (length - 1)] = HLIST_HEAD_INIT } }

- Josh Triplett


\
 
 \ /
  Last update: 2012-08-02 13:21    [W:0.071 / U:3.188 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site