March 2011 - Boost - lists.boost.org

Boost.Log status
by Vicente BOTET 23 May '11

23 May '11

Hi, what is going on Boost.Log? The library was accepted provisionally on March 2010 * Log - accepted provisionally March 2010; author: Andrey Semashev. Best, Vicente

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[boostcon][proto] Suggestion for LIAW session: fixed-point numbers
by Ravi 19 May '11

19 May '11

Hi, Are there any proto-based ideas for the library-in-a-week sessions? If not, would building a fixed-point data type be of interest? The domain is narrow enough that something useful can be accomplished in 4 sessions, but of large enough scope to present opportunities for exploring proto in depth. A fairly simple design follows representing a number: fixed_number<int width, int ulp, // 2^{ulp} is the smallest increment possible bool signed, template assigner<first, last, signed> > 'assigner' handles rounding/truncation/wrapping/etc when assigning another number (floating-point or fixed-point) to the current one. Internally, each fixed-point number would be represented by a boost::uint64_t or a boost::int64_t (limiting the maximum precision allowed). As an example, fixed_number<5, -3, false> would represent a data type that would go from 0 to 3.875 in steps of 0.125. Proto would be used for creating all arithmetic operations since the return type of a+b could be different from the type of either a or b. A bonus would involve getting the fixed-point data type to play well with std::complex (and, yes, I am aware that std::complex is not designed to work with anything other than double and float, and will require specialization in the std namespace). If there is sufficient interest, I could even provide a starting point with +,-,* implemented; / would take more time. The design above is intended as a starting point for discussion and I am most definitely not wedded to it. I am a tyro when it comes to proto, and hence would need someone with more proto expertise to guide the discussion. Regards, Ravi

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[local] Help for the Alternatives section
by Lorenzo Caminiti 12 May '11

12 May '11

Hello all, I am updating Boost.Local docs and I could use a some help in getting the Alternatives section right http://svn.boost.org/svn/boost/sandbox/local/libs/local/doc/html/boost_loca… . How can I program the following code (its local function and `factor` constant binding) using Boost.Phoenix, Boost.Lambda, and C++0x lambda functions? If you know, can you please reply with the actual code? #include <boost/local/function.hpp> #include <iostream> #include <vector> #include <algorithm> int main() { double sum = 0.0; int factor = 10; void BOOST_LOCAL_FUNCTION_PARAMS(double num, // Variable `factor` bound as constant. bind& sum, const bind& factor) { sum += factor * num; std::cout << "Summed: " << sum << std::endl; } BOOST_LOCAL_FUNCTION_NAME(add) std::vector<double> v(3); v[0] = 1.0; v[1] = 2.0; v[2] = 3.0; // Local function `add` passed as template parameter. std::for_each(v.begin(), v.end(), add); return 0; } Thank you very much! -- Lorenzo

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[atomic] Status?
by vicente.botet 04 May '11

04 May '11

Hi, There are some libraries that would prefer to be reviewed after Boost.Atomic is reviewed, otherwise them should move the library as an internal detail of the implementation. Could the people working on Boost.Atomic tell us what is the state of the library? Which platforms have been handled? Which part of the standard has been implemented? Could others having knowledge in assembler participate in this project? When we can expect the library to be ready for review? Best, Vicente

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accurate sum accumulator (kahan)
by Gaetano Mendola 27 Apr '11

27 Apr '11

Hi all, I had to implement in terms of boost accumulators the Kahan summation algorithm. I will paste at the end of this message the accumulator, the feature and the extractor source code. This accumulator reduces the numerical error obtained with standard sequential sum, as example the sum of 1e6f elements equal to 1e-6f should give 1.0f, this is the results obtained with sum and sum_kahan: tag::sum: 1.009038925 tag::sum_kahan: 1.000000000 I'm not sure if that sum_kahan is worth to be inserted in the accumulators provided with boost, I'm not an expert of boost:accumulators (I just followed the guide to make this new accumulator) so not sure if you prefer to have a fast_sum and an accurate_sum instead of sum and sum_kahan. Regards Gaetano Mendola // File kahan_sum.hpp #ifndef KAHAN_SUM #define KAHAN_SUM #include <boost/accumulators/framework/accumulator_base.hpp> #include <boost/accumulators/framework/parameters/sample.hpp> #include <boost/numeric/conversion/cast.hpp> namespace boost { namespace accumulators { namespace impl { template<typename Sample> struct sum_kahan_accumulator : accumulator_base { typedef Sample result_type; template<typename Args> sum_kahan_accumulator(Args const & args) : sum(args[sample | Sample()]), compensation(boost::numeric_cast<Sample>(0.0)) { } template<typename Args> void operator ()(Args const & args) { const Sample myTemp1 = args[sample] - this->compensation; const Sample myTemp2 = this->sum + myTemp1; this->compensation = (myTemp2 - this->sum) - myTemp1; this->sum = myTemp2; } result_type result(dont_care) const { return this->sum; } private: Sample sum; Sample compensation; }; }}} namespace boost { namespace accumulators { namespace tag { struct sum_kahan : depends_on< > { typedef impl::sum_kahan_accumulator< mpl::_1 > impl; }; }}} namespace boost { namespace accumulators { namespace extract { extractor< tag::sum_kahan > const sum_kahan = {}; } using extract::sum_kahan; }} #endif

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GSoC 2011
by mahbubul hasan 21 Apr '11

21 Apr '11

Hi, I am Mahbub. I am a CSE graduate. I just saw you had a proposal regarding queue and heap in GSoC 2010. In my undergraduate I did thesis on heaps. In that time I learned soft heap, it might be interesting to you. Here is the short description of soft heap<http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.85.3258&rep=rep1&t…>.( http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.85.3258&rep=rep1&t…) Soft heap is a heap like data structure but with some uncertainty. This data structure supports insert, delete, merge, findmin. It does every work in amortized constant time except insert operation which takes O( log 1/e ) where 0<e=<.5. Here e is error rate. The data structure will never contain more than en corrupted elements. There are two versions of soft heap. 1. By Binomial Tree 2. By forest of binary tree There is one more thing that might interesting to you. That is, in my undergraduate I improved the running time of heap sort by significant amount by applying pairing technique. The paper is submitted to International Journal of Computer Mathematics and it is under review now. It mainly improves Carlsson's variant of heapsort. It also improves the deletion method proposed by Gonnet and Munro (Heaps on Heaps). [The heap is inplace, that means no additional space is required] It also improves the Weak Heapsort. WeakHeapsort is a sorting method which requires O(n) additional bit to sort. However applying the pairing technique it can be reduced to O(n/2) additional bit. It is known that weakheap is the theoretically best known algorithm. [Best considering number of comparisons] So I am just curious if you are interested in these types of algorithms. I saw no possible proposal category where these fits in, but I thought you might be interested. Please let me know what do you think about this. Mahbub

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doxygen limitations
by Vicente BOTET 17 Apr '11

17 Apr '11

Hi, I would like to comment some limitations I have found while trying to generate the reference manual from the code comments using doxygen. 1. C++0x explicit operators are not documented as explicit with a warning explicit operator underlying_type const&() const ^^^^ gives operator underlying_type const &() const; 2. ::type misplaced when inheriting from a metafunction template < typename Final, typename UT, typename MetaMixinSeq=boost::mpl::vector0<>, typename Base=base_opaque_type > class new_class : public linear_hierarchy::type { gives template, typename Base = base_opaque_type> class new_class : public linear_hierarchy::type< MetaMixinSeq, Final, Base > { // ^^^^ 3. The base type is missing if the class is not documented elsewhere. This applies to other classes defined in other libraries in Boost or the Stl, but also when we use parameterized inheritance. template struct inherited_from_underlying { template struct type : Base { // Parameterized inheritance }; }; gives template struct inherited_from_underlying { // member classes/structs/unions template struct type { }; }; 4. When the brief comment takes only one line the comment is included on the Synopsis and nothing on the description section //! the underlying type typedef UT underlying_type; generates typedef UT underlying_type; // the underlying type 5. The classes are sometimes implicitly prefixed with his namespace template < typename UT, typename Tag=void, typename Bool=bool, typename MetaMixinSeq=boost::mpl::vector0<>, typename Base=base_private_opaque_type > class private_opaque_type : public private_opaque_class< private_opaque_type, UT, Bool, MetaMixinSeq, Base> gives template, typename Base = base_private_opaque_type> class private_opaque_type : public boost::opaque::private_opaque_class< private_opaque_type< UT, Tag, Bool, MetaMixinSeq, Base >, UT, Bool, MetaMixinSeq, Base > Do you have a workaround to some of these issues? What about creating a specific doxygen limitations and workarounds wiki page? Is there a possibility that the generated html goes to a single reference html file? Best, Vicente P.S. You can see directly some real examples on the documentation of Boost.Opaque https://svn.boost.org/svn/boost/sandbox/opaque/libs/opaque/doc/html/index.h….

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[GSOC]SIMD Library
by Faiçal Tchirou 12 Apr '11

12 Apr '11

Hi everyone, I recently ask documentation about the SIMD Library project here and I receive some guides and references links from Joel Falcou. Now I have some questions about the library itself. Is the goal of the project to build a library similar to libSIMDx86 but more focusing on the AltiVec instruction set ? Joel also advises me to take a look at Proto. I read that Proto is used to build DSEL. Will Proto be used to map high level classes and methods of the library to native SIMD instructions ? What about the library itself ? Which modules have to be developped ? Thanks.

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Proposed Library Boost.Algorithm
by Marshall Clow 09 Apr '11

09 Apr '11

(Finally) I have uploaded to the vault <http://www.boostpro.com/vault/index.php?action=downloadfile&filename=Boost.…> a proposal for the Boost.Algorithm library. This has been a matter of interest and discussion for a long, long time. Some of this code was written during the "Library in a week" session at BoostCon 2008. More was written last summer after this year's BoostCon. There is no way that I can write and submit all the algorithms that people want/need/are interested in, so I am proposing to set up a system by which people can submit algorithms to be included in the library, and have them reviewed, much like how new libraries are reviewed for acceptance into boost. The difference will be that a new algorithm is generally a much smaller piece of code than a new library, so hopefully we can lower the barrier to getting small pieces of code into Boost. So, what's in this proposal? 1) Three search algorithms: Boyer-Moore, Boyer-Moore-Horspool and Knuth-Morris-Pratt. (search.hpp) 2) A set of predicates for determining if a sequence is ordered (by some criteria) (ordered.hpp) Originally written by Grant Erickson during the "Library in a week" session at Boostcon 2008, and reworked somewhat by myself. 3) A set of predicates for determining other properties of a sequence, based on some suggestions for C++0x. (all.hpp) 4) An algorithm for restricting a value between two endpoints (clamp.hpp) And, of course, test cases and documentation. -- Marshall

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[GSoC] NLP Idea for GSoC 2011 project
by Sarma Tangirala 08 Apr '11

08 Apr '11

Hello list, I have worked with Boost on my projects but haven't really thought of using C++ as a language for NLP. The NLP that I have done is on Python and Java, for their built-in string methods. I don't know if this is inexperience or ignorance, but does C++ work well for NLP? I was thinking of having a GSoC project that is devoted to provide support for NLP. I mean like the kind that looks real easy on python. Also, I was looking at some C++ code using Boost/tokenizer.hpp that tokenized some text and it looked a bit scary. Any suggestions or advice? -- Regards, Sarma Tangirala, Junior - Class of 2012, Department of Information Science and Technology, College of Engineering Guindy - Anna University

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