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 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.

    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 }

    One downside: you can't use this to define a global non-static hash
    table, because you can't have a global non-static anonymous union.
    Using the non-union form would actually allow a global non-static hash
    table:

    #define DEFINE_HASHTABLE_INIT(name, bits) struct hash_table name = { .bits = bits, .buckets = { [0 ... ((1 << bits) - 1)] = HLIST_HEAD_INIT } }

    /* elsewhere */
    extern struct hash_table name;

    I don't know if that seems like a good idea or not.

    - Josh Triplett


    \
     
     \ /
      Last update: 2012-08-02 19:01    [W:0.051 / U:33.344 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site