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boost::crc - newbie help
by Paul Caswell 08 Jan '10

08 Jan '10

Hello all, I've the task of implementing the following CRC computation and was wondering whether I could use boost::crc to save me a lot of hassle. ------------------------ Default 32-bit Parity (CRC) This 32-bit CRC is the same as that described in EKMS 304 ([6]) and EKMS 322 ([8]) and could be used as a CRC method in the keyAlgorithm Attribute (with OID { 1 2 826 0 1145 0 5 1 }). Let g(x) be the polynomial x32 + x22 + x2 + x + 1. Let d(x) be the k bits of data to have parity applied to them. The first bit of data is the coefficient of the (k-1)st power of x etc. Let f(x) be the polynomial naturally represented by the initial fill 0xF8DD4258, i.e. x31 + x30 + x29 + x28 + x27 + x23 + x22 + x20 + x19 + x18 + x16 + x14 + x9 + x6 + x4 + x3. Then the output is c(x) = x32d(x) + xkf(x) mod g(x). The polynomial c(x) is then interpreted as a stream with the coefficient of x31 coming first and the coefficient of x0 coming last. The 32-bit parity is then c(x). This calculation can be done using a simple shift register as shown below. The shaded stages represent ones in the initial fill. The logic steps k times to determine c(x), which is the final state of the register. <diagram omitted> ------------------------ Any advice and or help would be appreciated. Regards, Paul This email and any files transmitted with it may be confidential, legally privileged and protected in law and are intended solely for the use of the individual to whom it is addressed. Any view or opinions presented are solely those of the author and do not necessarily represent those of Stonewood Group Ltd. If you have received this Email in error please contact the sender by return and confirm that its contents have been destroyed without further distribution or disclosure. Please email admin(a)stonewood.co.uk with any questions relating to this disclaimer. Stonewood Group Ltd has Registered Offices at Sandford Lane, Wareham, Dorset BH20 4DY. The company is registered in England and Wales under no: 3007498.

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Thread not interrupted in runtime linked library
by Lloyd 08 Jan '10

08 Jan '10

Hi, Using boost thread a new thread is created. The thread loads a DLL using LoadLibrary() call, gets the procedure address by calling GetProcAddress() and executes the procedure. The body of procedure is an infinite loop. When I try to interrupt the thread from main thread it is not interrrupted! What could be the reason? In all other cases the thread is interrupted except when it is inside the dynamically (runtime) linked library procedure. What could be the reason? Please share some idea... Thank you very much Lloyd ___________________ Happy New Year 2010

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Xpressive continuing search from previous match
by K. Noel Belcourt 08 Jan '10

08 Jan '10

Hi, I have a search for a regular expression like this. sregex_iterator cur(buffer.begin(), buffer.end(), defined_re), end; for(; cur != end; ++cur) { ... But what I really want to do is perform a new regex search starting at the location in the buffer marking the end of the previous search. Is there a way to get the buffer index from the previous search so I can start the new search past the previous search? I apologize if this is easy to do, I must have missed it with my quick perusal through the documentation. Thanks. -- Noel Belcourt

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Defining Statements with Proto
by David A. Greene 08 Jan '10

08 Jan '10

A few years ago, I asked how to define a grammar with Proto to match something like this: if_(expr) [ stmt, stmt, ... ].else [ stmt, stmt, ... ]; The answer was to do this: struct Grammar; struct ExpressionGrammar; struct StatementGrammar; struct Domain; template<typename Expr> struct Expression : proto::extends<Expr, Expression<Expr>, Domain> { typedef proto::extends<Expr, Expression<Expr>, Domain> base_type; Expression(Expr const & expr = Expr()) : base_type( expr ) {} }; struct Domain : proto::domain< proto::generator< Expression >, Grammar> {}; struct If {}; BOOST_PROTO_DEFINE_FUNCTION_TEMPLATE( 1 , if_ , Domain , (If) , BOOST_PP_SEQ_NIL ); // Here is the grammar for if_ statements // matches if_(e1)[e2] struct IfGrammar : boost::proto::subscript< boost::proto::arg< boost::proto::unary_expr< If, ExpressionGrammar >, >, StatementGrammar > {}; // An else_ "operator" template<typename Expr> struct Expression< Expr , typename enable_if<proto::matches<Expr, IfGrammar> >::type > : proto::extends<Expr, Expression<Expr>, Domain> { Expression() : else_(proto::make_expr<Else>(*this)) {}; proto::result_of::make_expr< Else, // else is now an "operator" Expression<Expr> const >::type const else_; }; // matches if_(e1)[e2].else_[e3] struct IfElseGrammar : boost:proto::subscript< boost::proto::arg< boost::proto::unary_expr< Else, IfGrammar >, >, StatementGrammar > {}; I didn't understand it then and I don't now. :) However, it seems to be obsolete since BOOST_PROTO_DEFINE_FUNCTION_TEMPLATE doesn't seem to exist anymore (it's not documented, anyway). So how would this be formulated in modern Boost.Proto? I'm guessing I will need an expression template wrapper (called Expression<> above) that uses some combination of BOOST_PROTO_BASIC_EXTENDS, BOOST_PROTO_EXTENDS_SUBSCRIPT and BOOST_PROTO_EXTENDS_FUNCTION. But of course not all statements have a valid operator() overload and no expressions do. I guess the grammar will take care of that, yes? I'm really puzzled about how to do the ".else_" part. I was hoping I could look to Phoenix to get a clue but it doesn't seem to use Proto. Any help? Thanks! -Dave

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[foreach] BOOST_FOREACH question...
by barcaroller 08 Jan '10

08 Jan '10

Does the BOOST_FOREACH macro work for empty sequences or must a size check be done explicitly? list<int> mylist; if (!mylist.empty()) // <--- necessary? { foreach(int& i, mylist) { // take action } } The reason I ask is that neither begin() nor end() return valid iterators for empty sequences, but it is my understanding that BOOST_FOREACH needs iterators to work properly.

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fusion and mpl
by Peter Foelsche 08 Jan '10

08 Jan '10

I need to be able to convert a mpl sequence into something like a tuple: typedef boost::mpl::vector<double> CMplSequence; typedef CCreateVectorFromMpl<CMplSequence>::type CVector; I need to have runtime access with constant index: CVector s; get<0>(s) = 1.0; std::cout << get<0>(s) << "\n"; I need to be able to retrieve the type at compile time: typedef CGetType<CVector, boost::mpl::long_<0> >::type CFirstType; I already wrote something like this using std::pair as the tuple but I'm running into problems storing reference types on Windows. Peter

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boost::multi_array equivalent for runtime number of dimensions
by Hicham Mouline 07 Jan '10

07 Jan '10

Hello, I only know at runtime the dimension and extends of a multidimensional array, though the number of dimensions is always < 10 for e.g. Is there a container that allows this? Otherwise, I can write code for multi_array<T, 2> multi_array<T, 3> . multi_array<T, 10>, do a switch case on the dimensions variable, and select the appropriate code, regards,

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[Math/Statistical Distributions+Random] Random number generation
by Marco Guazzone 07 Jan '10

07 Jan '10

Hi all! I'm a "boost newbie" so sorry for too trivial questions. Just trying to use boost for some statistical experiments, involving statistical distribution fitting, quantile generation (for goodness-of-fit tests), random variate generation, and so on. . The "Math/Statistical Distribution" library is great and almost complete. But I'm just curious why the random number generation (provided by the "Random" lib) and this library have not been integrated. For instance, the boost::random::exponential_distribution and the boost::math::exponential_distribution are two different worlds. I think a function like this below would be very helpful: --- [snip] --- template <typename Generator, typename RealType, typename Policy> inline RealType rand(Generator& rng, const exponential_distribution<RealType, Policy>& dist) { return -1.0 / dist.lambda() * std::log(1.0-rng()); } --- [snip] --- or something similar (e.g., rand implemented as a class method) In this case only two objects are needed: * boost::random::mersenne_twister * boost::math::exponential_distribution Instead, actually I have to keep different objects. For instance, for the exponential distribution: * boost::random::exponential_distribution * boost::random::mersenne_twister * boost::random::variate_generator * boost::math::exponential_distribution Unluckely I can't use boost::math::exponential_distribution in place of boost::random::exponential_distribution since boost::random::variate_generator expects a specific interface for the distribution. Well, what is the rationale behind the choice of this separation? Do you think would be useful to provide this kind of integration? Thank you very much in advance!! Cheers -- Marco

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Re: [Boost-users] BGL: shared_ptr as bundled properties > how to generate properties maps ???
by Damien Maupu 07 Jan '10

07 Jan '10

>On Wed, 6 Jan 2010, Emil Dotchevski wrote: > > On Wed, Jan 6, 2010 at 8:20 AM, Damien Maupu <damien.maupu_at_[hidden]> wrote: >>> I write something like: >>> typedef boost::shared_ptr<Vertex> VertexPtr; >>> typedef boost::shared_ptr<Edge> EdgePtr; >>> typedef adjacency_list<vecS, vecS, directedS, VertexPtr, EdgePtr> Graph; >> >> It is probably not a good idea to use shared_ptr for graphs; some >> graphs have cycles and this will lead to leaks (if your data structure >> is a DAG, you're fine.) >I don't think that will be an issue -- his shared pointers link to >properties; the graph structure itself is in BGL data structures. >However, if the properties refer to other graph vertices or edges, there >is an issue of dangling references if those objects are removed from the >graph. >-- Jeremiah Willcock Hi, I am not sure I understand why using smart pointer should be an issue. Could you explain me in little more details? Do you know how to get properties maps if bundle properties are pointer or smart pointers? Thank you Damien

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ASIO async_read_until with condition + strand
by Christophe Bourez 07 Jan '10

07 Jan '10

Can someone help with the boost async_read_until with condition ? I need to implement a request/response protocol. * A request cannot be send until the response has been completely read from the server. * Response's length from the server is unknown. The data must be parsed thanks to a parser to understand the content of the buffer. The parser is capable to return a code specifying whether the data is complete, which could require more reading on the socket. I'd like to implement my client asynchronously using ASIO. Here is the solution I implemented: the async send handler calls async_read whose handler calls async_read handler again until the message is complete. Due to the here above constraints, I am forced to queue the requests and async send the next request by the end of the handler of the current response (when it is complete, otherwize it async_reads again). I have tried to use async_read_until with a condition, but the parser was invoked very (too) often (every 2 bytes) and penalizes the performance. Would it be possible to reduce the number of calls to the condition (by reading at once the maximum of bytes present on the socket for example)? I'd like to async send the requests as soon as I can, in order to avoid the queue. Is it possible to implement a solution by using the ASIO strands? If yes, I have the feeling that the way I implemented the response handling will not work with the strand because the handler of async_read calls async_read again, which will probably come at the end of the strand's queue (which may contain many async_send requests). Could async_read_until with a condition solves this issue by avoiding to async_read again? Any help will be very appreciated. Christophe

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