November 2015 - Boost - lists.preview.boost.org

[variant] Opinion on boost::safe_get<> and default boost::get<> behavior
by Antony Polukhin 18 Dec '15

18 Dec '15

Hi all, I'm in doubt and would like to hear opinions on the following issue. boost::get for boost::variant was not making any compile time checks, resulting in runtime errors where a compile time error must be: boost::variant<int, string> v(100); boost::get<bool>(&v); // returns NULL instead of compile time error boost::get<bool>(v); // throws exception on runtime instead of compile time error Now we have an implementation of compile time checked get in a separate branch at git: boost::variant<int, string> v(100); boost::safe_get<bool>(&v); // compile time error boost::safe_get<bool>(v); // compile time error boost::unsafe_get<bool>(&v); // returns NULL instead of compile time error boost::unsafe_get<bool>(v); // throws exception on runtime instead of compile time error I'm in doubt, what the default behavior of boost::get must be: * safe_get behavior is much closer to Standard Library behavior (just like std::get for tuples) and allows to avoid errors in user code * unsafe_get behavior is same as behavior of old boost::get and won't break user's code if boost::get is used in some generic contexs What's your opinion? -- Best regards, Antony Polukhin

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[LOG] formatting_ostream API change
by Andrew Hundt 09 Dec '15

09 Dec '15

I had the following code, which worked in 1.58: #include <boost/log/trivial.hpp> #include <boost/exception/all.hpp> #include <boost/algorithm/string.hpp> /// @todo move elsewhere, because it will conflict with others' implementations of outputting vectors template<typename T> inline boost::log::formatting_ostream& operator<<(boost::log:: formatting_ostream& out, std::vector<T>& v) { out << "["; size_t last = v.size() - 1; for(size_t i = 0; i < v.size(); ++i) { out << v[i]; if (i != last) out << ", "; } out << "]"; return out; } I used it to output a std::vector<float> as follows: BOOST_LOG_TRIVIAL(trace) << “Real joint angles from FRI: " << realJointPosition << "\n"; However this now seems to fail in 1.59. I’ve created a github gist with the compiler output <https://gist.github.com/ahundt/5869dbd09e889b7153c3> in case that’s helpful as well. I see that the update recently had some breaking changes, what is the new way to provide the desired functionality? Thanks for your help. Cheers! Andrew Hundt

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interest in an asynchronous linear algebra library?
by Oswin Krause 07 Dec '15

07 Dec '15

Hi list, Disclaimer: What I am proposing here does not exist (yet). But it will in the near future and if there is interest i would like to give something back to the boost community. I would like to propose a new library to boost: asynchronous blas. What is it and what can I do with it? It is a linear algebra library where all computations are carried out in an asynchronous manner on GPU and CPU. Computing a matrix-matrix product does not block the current thread but instead launches a task which at some point returns with a result, allowing the main thread to continue until the result is needed. GPU and CPU tasks can be started at the same time depending on each other (e.g. a CPU computation waits until the GPU returned some needed result and vice-versa) Why is this important? Which problems does it solve? Many linear algebra libraries are target towards either a) solving a few large linear algebra problems b) solving many small similar problems This library is targeted towards the middle ground: a medium amount of decently sized problems. Here the problem is that it is often hard to use all the computing resources available as a single problem will not exhaust the device resources and there is no easy way to launch several similar tasks in parallel. This problem occurs often in GPU computing where out-of-order execution of kernels is used to fill up the device. Similarly, it is often hard to make CPU and GPU work together as GPU tasks are asynchronous while CPU tasks are often synchronous and it is not straight forward to couple both without blocking either CPU or GPU. How does it work? Expression templates similar to boost::ublas are used to create a dependency graph: which object is used in which computations and which tasks have to wait to ensure a correct outcome? a simple case would be two independent computations like matrix A=prod(B,trans(B)); matrix C=prod(trans(B),B); a normal library like ublas would wait until A is computed before C is evaluated. Instead, it can be more efficient to just add the two tasks to a list and let worker threads execute them as soon as resources are available. First the computation of A is put into the graph and A is marked as "being written to" while B is marked as "being read". When C is added to the list, it does not depend on the first computation as several tasks can read from B at the same time. So another worker thread can grab the task and execute it. If we now add the task B += prod(D,prod(C,trans(D)); the library computes it as matrix temp = prod(C,trans(D); B += prod(D,temp). temp can be computed as soon as C is computed. But B can only be computed after A and temp are computed as we can only write to B after all previous tasks using B are finished. Are you qualified? I am main contributor to https://github.com/Shark-ML/Shark/ and as part of it I forked ublas https://github.com/Shark-ML/Shark/tree/master/include/shark/LinAlg/BLAS which now uses several linear algebra libraries as possible backends (ATLAS, openBLAS...). What is the timeline? I would start developing a minimal example ASAP based on the rewrite of ublas above. I would use a minimum set of features (only dense square matrices) and basic GPU support. Opinions? Best, Oswin

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Boost 1.60.0 beta 1 Release Candidate 2 available for testing
by Marshall Clow 04 Dec '15

04 Dec '15

Release candidate files for 1.60.0 beta 1 are available at http://boost.cowic.de/rc/ As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. This helps ensure the candidates build OK before we push them out to SourceForge. Changes since rc1: * Boost.Sprit has been updated and Boost.Log now builds. * Boost.Math has been updated and now builds. Known issues: * Errors when building libraries for visual studio: test and type_erasure. * Boost.Test fails when building on Darwin with gcc 4.9.2 The files (and associated md5s) are: MD5 (boost_1_60_0_b1_rc2.7z) = dd38daa9378a6002fc12da0cab695511 MD5 (boost_1_60_0_b1_rc2.tar.bz2) = f3c9ffc14db3b2e55c7c5c703e69883d MD5 (boost_1_60_0_b1_rc2.tar.gz) = 89365262443cc16990b69f8e4b8b47ab MD5 (boost_1_60_0_b1_rc2.zip) = 3389bd4595a989fe95966440cbe45ca9 Thanks! -- The release managers

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compilation errors with ublas / cppad
by Peter Caspers 30 Nov '15

30 Nov '15

Hi, I think this has been asked before, but since I am not aware of any answer, I would like to bring up the topic again: When using CppAD::AD<double> with boost ublas, certain compilation errors show up. I attach a small example (ublas_cppad.cpp) and the (start of the) error messages I get (compilation_errors.txt, produced with boost 1.59.0, g++ 4.9.3, CppAD-20151124). The problem is in matrix_assign.hpp; when changing template<class E1, class E2, class S> BOOST_UBLAS_INLINE bool equals (const matrix_expression<E1> &e1, const matrix_expression<E2> &e2, S epsilon, S min_norm) { return norm_inf (e1 - e2) < epsilon * std::max<S> (std::max<S> (norm_inf (e1), norm_inf (e2)), min_norm); } to template<class E1, class E2, class S> BOOST_UBLAS_INLINE bool equals (const matrix_expression<E1> &e1, const matrix_expression<E2> &e2, S epsilon, S min_norm) { S tmp = norm_inf (e1 - e2); return tmp < epsilon * std::max<S> (std::max<S> (norm_inf (e1), norm_inf (e2)), min_norm); } the example code compiles without errors. Can someone point out, how this should be fixed (either on boost or CppAD side)? In general, are there requirements for a type T to cooperate with ublas matrices one should be aware of? Thank you Peter

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Is master branch open for bug fixes?
by Vicente J. Botet Escriba 30 Nov '15

30 Nov '15

Hi, the calendar says that master branch is open for bug fixes, but not mail has been sent to to notify it. Could some release manager confirm that? Best, Vicente

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[program_options] empty string argument
by Benedek Thaler 30 Nov '15

30 Nov '15

Hi, I have the exact same problem: http://boost.2283326.n4.nabble.com/ProgramOptions-explicit-empty-string-arg… --compression '' gave me a specified, empty compression switch value, as expected, on boost 1.58. However, on 1.59, the empty string counts against the positional arguments, and causes regressions. Also, --compression='' gives: The argument for option '--compression' should follow immediately after the equal sign. What is the recommended workaround? Is it planned to be fixed/changed? Thanks, Benedek

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[Boost.LLVM] Synopsis now available
by Andy Jost 29 Nov '15

29 Nov '15

I've created a new GitHub repository for this project and uploaded a synopsis of the proposed interface. I redesigned the interface, so it differs slightly from the prototype code and examples I gave before. Please take a look and provide feedback if you can! https://github.com/andyjost/Boost.LLVM/blob/master/boost_llvm.cpp -Andy

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Interest in an LLVM library?
by Andy Jost 26 Nov '15

26 Nov '15

Is there interest in an LLVM library? My motivation is to simplify the dynamic creation of functions, modules, and programs by defining an EDSL modeled after the C language. LLVM provides an API based exclusively on function calls that is verbose and difficult to use. The EDSL is more expressive and easier to use. (This may remind some people of Boost.Python and indeed these libraries are similar in motivation.) The scope of this proposal is limited. The proposed library does not compile, link, optimize, save, or load anything, for example, since the LLVM API is suitable for that. Also, it may not support obscure features, even if they seem to be within its purview, since one can always make direct calls to the LLVM API. I have written about 6500 lines of prototype code in the context of another project (a compiler for the language Curry, if anyone is interested). It is not a complete solution, but is by no means trivial, either. I'll discuss that next, but since the discussion is somewhat lengthy, let me first explain what I'm looking for by sending this. I think this EDSL would make a good Boost library. If others agree, then the next step is to review the design. I need second opinions and help from more knowledgeable people to improve the design. There are a few places in particular where I think a redesign is necessary. After that, I'm happy to implement the final library (and would gladly accept help, if anyone is interested). Now, I'll show a few examples and provide links to the prototype code. First, here's how to create a module and put it in scope: module const example_module("example"); scope _ = example_module; The scope object sets the insertion point for types, functions, and global variables. We can create a type as follows: type i32 = int_(32); i32 is a 32-bit integer. It is easy to build more complex types, e.g., i32[2] is an array type, *i32 is a pointer type, and i32(i32,i32) is a function type. An expression like i32(42) produces a constexpr. As you might guess at this point, the prototype makes heavy use of SFINAE. I've gone to a lot of effort to make this work with everything I can think of, particularly multi-dimensional arrays and initializer_lists. So, an expression like (i32[3][2])({{1,2,3},{4,5,6}}) works! (Note: i32[3][2] is the C++ type int32_t[2][3] because that's the only sensible way to interpret successive calls to operator[]). We can create a struct from a sequence of types like this: type foo = struct_("foo", {i32, *i32}); Or, we can leave out the sequence to get an opaque struct. A function prototype can be created as follows: function const f = extern_(i32(i32), "f", {"i"}); This function, f, takes an i32 (named "i") and returns an i32. The function is placed in example_module, since the code appears in its scope. There are two other linkage-specifying functions: static_ and inline_. extern_ and static_ are also used to create global variables (i.e., if the type is not a function). To define the body, we create another scope: { scope _ = f; // code for f. } To understand this, we have to discuss scopes in more depth. There are three nested levels of scope: the current module, the current function, and the current basic block. The code above sets the current function to f and the current basic block to f's entry point. Generally speaking, within a function body we write statements that generate instructions. Those instructions are inserted into the current function at the end of the current basic block. To define the body, we can declare values and operate on them. For example: value i = arg("i"); Here, "arg" is a special function that fetches the named function parameter. We can add instructions to f using operators or special methods. For example: value j = i + 1; return_(j); Branches manipulate the current basic block. Here's an if statement: label true_path, false_path; if_(i, true_path, false_path); { scope _ = true_path; // code for true. } /* else */ { scope _ = false_path; // code for false. } // new basic block here. This generates instructions to test i, take the appropriate branch, and then continue to a new basic block in the right places (which depends on whether the paths terminate with a branch instruction). It also updates the scope so that statements following if_() are inserted into the new basic block. Believe me when I say it is not trivial to do this with the LLVM API. Although it is sometimes necessary to pre-declare labels as shown above, we can usually employ C++11 lambdas to simplify the encoding: if_(i , []{ /* code for true */} , []{ /* code for false */ } ); The prototype code can be found under https://github.com/andyjost/Sprite-3/tree/master/include/sprite/backend. Also, there are many examples under https://github.com/andyjost/Sprite-3/tree/master/examples. Other parts of the Sprite-3 project are unrelated to this proposal. A good example to start with generates the Fibonacci numbers (https://github.com/andyjost/Sprite-3/blob/master/examples/fib.cpp) Here's the interesting part: // Create a new module and associate it with this lexical scope. module const fib_module("fib"); scope _ = fib_module; // Declare types. auto const char_ = types::char_(); auto const i32 = types::int_(32); auto const i64 = types::int_(64); // Declare external functions. auto const printf = extern_(i32(*char_, dots), "printf"); // Define the @fib function. auto const fib = extern_(i64(i64), "fib", {"n"}); { scope _ = fib; value n = arg("n"); if_(n <(signed_) (2), []{return_(1);}); return_(fib(n-2) + fib(n-1)); } // Define the @main function. auto const main = extern_(i32(), "main"); { scope _ = main; value const x = fib(5); printf("fib(5)=%d\n", x); return_(0); } After this code runs, fib_module contains an intermediate representation of the program. The LLVM API can be used to save that to disk, compile it to assembly, link in the C library (to get printf), or JIT compile any of the functions, among other things. Thanks to everyone who made it this far :) I'm looking forward to your feedback. -Andy

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[trippels-ppc64le][math] Missing quadmath.h errors
by Andrey Semashev 24 Nov '15

24 Nov '15

Hi, I'm seeing some test failures on the trippels-powerpc64le-gcc-6.0 tester that amount to Boost.Math failing to build because the quadmath.h header is missing. http://www.boost.org/development/tests/develop/developer/output/trippels-po… I understand that gcc 6.0 is an unreleased compiler, but the error is probably not a consequence of a compiler bug. Besides, another tester, Flast-FreeBSD10-gcc-6.0.0~gnu++11, passes. Is it possible that the header is not provided for powerpc64le? Or is an optional dependency whose presence is misdetected? Is this a known problem?

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