Johan Hake wrote:
> On Tuesday 06 October 2009 22:18:04 Anders Logg wrote:
>> On Tue, Oct 06, 2009 at 09:13:45PM +0100, Garth N. Wells wrote:
>>> Anders Logg wrote:
>>>> On Tue, Oct 06, 2009 at 10:05:24PM +0200, Johan Hake wrote:
>>>>> On Tuesday 06 October 2009 21:58:29 Andy Ray Terrel wrote:
>>>>>> On Tue, Oct 6, 2009 at 2:43 PM, Anders Logg <l...@simula.no> wrote:
>>>>>>> On Tue, Oct 06, 2009 at 02:28:40PM -0500, Andy Ray Terrel wrote:
>>>>>>>> Sorry for being dense but computing the SHA1 hash for what
>>>>>>>> essentially is a string compare seems a bit overkill.
>>>>>>> I want to avoid a call to strcmp in a piece of code that needs to be
>>>>>>> fast. What I do (it seems to work now) is to compute the 20 byte
>>>>>>> SHA-1 hash from the ~40 byte finite element signature which is
>>>>>>> typically something like
>>>>>>>
>>>>>>> FiniteElement('Lagrange', 'triangle', 1)
>>>>>>>
>>>>>>> I then cast the SHA-1 hash to an 8 byte void* and use that for
>>>>>>> comparison. This may not be very safe but this is not exactly
>>>>>>> cryptography. The number of possible hashes is the same as the
>>>>>>> address space so it should be fine.
>>>>>> Yes I guess if you have a large number of comparisons it might be
>>>>>> faster. I forget there are a lot of signature checks for the
>>>>>> function space stuff.
>>>>>>
>>>>>> Computing the hash is O(n) just like strcmp, it really depends on the
>>>>>> constants. I would just do the timing before I said anything.
>>>>> Would it be an idea to extend ufc::finite_element with a
>>>>> hash_signature()? Then you can compute the hash using hashlib in
>>>>> python during code creation.
>>>>>
>>>>> Johan
>>>> Sounds like a good idea. Only it requires changes to DOLFIN, UFC, FFC
>>>> and SyFi...
>>>>
>>>> Are there any objections to this?
>>> I'm not sure that this is a good idea. It complicates UFC.
>
> Complicates? One function returning a string?
How would I write it by hand? It's common for new methods that the
UFC-compliant code is hand generated.
Garth
But I agree with Anders that it
> requires a lot to change and that it therefore is a good thing to think about
> it.
>
>> It's either that or using boost. I'm looking at both options.
>>
>> Calling boost is simpler since it requires the smallest change. If we
>> decide to go with that option now, we can keep this in mind for the
>> next update of UFC.
>
> Sounds good.
>
> Johan
>
>> --
>> Anders
>>
>>> Garth
>>>
>>>>>> I looked there are a lot of libraries out there for this but OpenSSL
>>>>>> is by far the most pervasive.
>>>>>>
>>>>>> -- Andy
>>>>>>
>>>>>>>> On Tue, Oct 6, 2009 at 2:18 PM, Anders Logg <l...@simula.no> wrote:
>>>>>>>>> I'm contemplating adding a dependency to OpenSSL for computing
>>>>>>>>> hashes of things like element signatures.
>>>>>>>>>
>>>>>>>>> This is what breaks Kristian's code. Comparing element pointers
>>>>>>>>> does not work since the UFC class creates its own elements which
>>>>>>>>> are different from the ones existing in FunctionSpace classes.
>>>>>>>>>
>>>>>>>>> Would there be any difficulties with depending on OpenSSL? Are
>>>>>>>>> there simpler alternatives for a function that takes a string a
>>>>>>>>> returns a message digest like the SHA1 function in OpenSSL?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> -----BEGIN PGP SIGNATURE-----
>>>>>>>>> Version: GnuPG v1.4.9 (GNU/Linux)
>>>>>>>>>
>>>>>>>>> iEYEARECAAYFAkrLmCAACgkQTuwUCDsYZdEk3ACgl7+tHjclHzLesh+g/1vOzIo9
>>>>>>>>> tJsAn1fHGu+dzyA/ndNpy88/RFWNTbEB
>>>>>>>>> =24AA
>>>>>>>>> -----END PGP SIGNATURE-----
>>>>>>>>>
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>>>>>>> -----BEGIN PGP SIGNATURE-----
>>>>>>> Version: GnuPG v1.4.9 (GNU/Linux)
>>>>>>>
>>>>>>> iEYEARECAAYFAkrLndAACgkQTuwUCDsYZdFlWACePT0FglJU+NTPnOBXi/h7WcHC
>>>>>>> E5EAn2vinxerlg6jTNuA4T+0Kp+CFuhz
>>>>>>> =68Dm
>>>>>>> -----END PGP SIGNATURE-----
>>>>>>>
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>>>>> --
>>>>>
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