Re: RFC: sorted value_string + bsearch

[Anders Broman <anders.broman () ericsson com>]

-----Original Message-----
From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Jakub Zawadzki
Sent: den 22 april 2010 15:40
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] RFC: sorted value_string + bsearch

On Tue, Apr 20, 2010 at 11:43:49PM +0200, Anders Broman wrote:
> > Would it be faster to use hash tables instead of very large 
> > value_strings? In diameter i think 3gpp AVP codes are in a 
> > value_string > 2k
>
> I think main problem with hash tables, is that you need to have big table, and good hash function.
>
>
> Binary search is O(log2 n), so for 5k we have at most 13 lookups.
> To achieve it with hash table we need 384 (5000/13) buckets (HASHPORTSIZE in addr_resolv.c is only 256).
>
> And I think it's hard to implement hash tables, using current value_string ABI.
>
> Cheers.
Disclaimer: Hobby C programmer :-)

A crude sketch:
I was hoping it would be possible to provide a pointer to the hash table like:
-       { &hf_diameter_vendor_id,
-                 { "VendorId", "diameter.vendorId", FT_UINT32, BASE_DEC, VALS(sminmpec_values),
-                         0x0,NULL, HFILL }},
+       { &hf_diameter_vendor_id,
+                 { "VendorId", "diameter.vendorId", FT_UINT32, BASE_DEC, HASH_VALS(hastablep),
+                         0x0,NULL, HFILL }},

Use g_hastable_new_full() gint version and stuff the value_string into the hash table
In proto_register, then have proto.c extract the value. Alternatively we could perhaps
Pass a "get_value" function pointer?
 I'm not sure this will work :-)

Regards
Anders
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