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[1.53] [multiprecision] Still time for bug fixes?
by John Maddock 12 Jan '13

12 Jan '13

If there's still time (and the test results need to cycle first), I'd like to merge this bug fix: https://svn.boost.org/trac/boost/changeset/82460 for this bug: https://svn.boost.org/trac/boost/ticket/7878 Which causes integer division to fail in some cases. Thanks, John.

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Re: [boost] [non-instrusive move] interest in new library?
by THOMAS JORDAN 11 Jan '13

11 Jan '13

Thomas Jordan wrote: >Jeffrey Lee Hellrung, Jr. wrote >> You didn't really expound on the implementation, but, if I had to guess, >> you'd also require your types to be default constructible, and it would >> perform suboptimally (worse than leaving the move call out) if the swap >> member function was equivalent to std::swap. I think this might preclude >> its use in generic contexts and limit its use to situations where you >> *know* the type is std::vector-like. Let me know if I'm presuming >> incorrectly :) >> > >Yes, it certainly requires the types to be default constructible. > ><snip> > >The alternative would be to have just the single, default, template move >function: > >//pseudo-code >move(T& left, T& right) > >plus a pair of template functions to move to and from temporaries >respectively: > >T move(T& x) >void move(const T& from, T& to) > >then have optimised move functions defined on a per-type basis, e.g., > >MyClass >{ > void swap(MyClass& other) > { > //efficient swap member > } > > friend void swap(MyClass& lhs, MyClass& rhs){} > > friend void move(MyClass& lhs, MyClass& rhs) > { > lhs.swap(rhs); > } >} > >as well as overloads defined for any cheap-to-swap library types >interested in: > >void move(std::vector& lhs, std::vector& rhs){} >void move(boost::function& lhs, boost::function& rhs){} >etc. > >Although this is safer in that it should ensure optimality - and is >actually where I started - it requires more boilerplate to be written, >though there may be way(s) to automate the generation of the the >user-type's move function. Also, with the library move functions >implemented like this, you could still write algorithms like >move()/move_backwards() (and helper functions >such as iter_move() to move the values between two iterators) generically. Also generic overloads of the move() function would be provided for built in arrays and e.g., boost::array //pseudocode void move(boost::array<T,N>& from, boost::array<T,N>& to){} void move(T (& left)[N], T (& right)[N]){} which would be implemented with a call to move(left[i], right[i]) for each element, in which case the elements would be swapped if a move overload has been defined for the element type, copied otherwise, thereby preserving optimality. It would work for multi-dimensional (boost) arrays in a recursive fashion. >So I guess the new question is, would this even smaller library be of >any interest? >Its use-cases would be the same as described in my original post, just >to reiterate: > >//use-case: returning a argument directly from a function > >std::string foo(std::string s) >{ > //e.g., append something to s > //... > > //compiler can perform rvo (compiler would likely not > //perform nrvo if just used 'return s;') > > return move(s); >} > > >//use-case: moving a value to a function/ctor, when the value is not >//required by the calling code after the function/ctor call > >std::string s("hello"); >void bar(std::string s){...} > >bar(s); //copy >bar(move(s)); //move >//s has now been moved out of > > >//use-case: moving a value into place >void MyClass::MyClass(std::string s) >{ > //move value from s into default constructed member s_ > move(s, s_); >} > >Note that the combination of both moving a value to a function/ctor and >then moving it into place, e.g., > >std::string lv; >//... > >MyClass mc(move(lv)); > > >effectively results in a zero-copy invocation, with just a small number of >fixed size swap, default ctor and shallow dtor calls, so this is pretty >efficient. >//use-case: moving a temporary into an lvalue >std:: string lv; >move(foo(), lv); > > >> - Jeff >Tom Tom

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Re: [boost] [non-instrusive move] interest in new library?
by Thomas Jordan 11 Jan '13

11 Jan '13

Joseph Gauterin wrote: > Out of curiosity, how are you detecting if a member function swap exists? >> it detects at compile-time if the type of the >> argument(s) has a member swap function //Type trait to determine whether a type has a swap() member function //Uses SFINAE and the "sizeof trick" from the book "C++ Template Metaprogramming" //by Abrahams and Gurtovoy template<typename T> struct has_swap { typedef char yes; typedef char (&no)[2]; //SFINAE eliminates this when the type is invalid template <typename U, U> struct Check; //this overload will be selected if the Check type is valid template <typename U> static yes Tester(Check<void(U::*)(U&), &U::swap>*); //overload resolution prefers anything at all over ... template <typename U> static no Tester(...); static bool const value = sizeof(Tester<T>(0)) == sizeof(yes); }; > > In general, there's no way of knowing if a member swap function is > more efficient than a single assignment. It isn't even for all the > examples you gave - boost::array<T,N>::swap performs N boost::swaps, > which, if T doesn't provide an efficient swap, results in N calls to > std::swap, and 3*N assignments. In general I'm wary of using swap in a > generic context unless the intent is to swap (i.e. not as a potential > optimization of assignment). Thanks, point taken. I've responded to the exact same point in Jeffrey Lee Hellrung Jr.'s comment on my original post, and also made some alternative suggestions. Would certainly appreciate any further feedback you have there.

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Boost.Exception and constexpr
by Marshall Clow 10 Jan '13

10 Jan '13

I was playing around with Boost.Array tonight, seeing if I could make the signatures more closely match std::array. Specifically, I wanted to add 'constexpr' to "operator [] (size_t) const" and "at (size_t) const"as proposed in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3470.html But I ran into a problem. Here are the implementations: const_reference operator[](size_type i) const { BOOST_ASSERT_MSG( i < N, "out of range" ); return elems[i]; } const_reference at(size_type i) const { rangecheck(i); return elems[i]; } static void rangecheck (size_type i) { if (i >= size()) { std::out_of_range e("array<>: index out of range"); boost::throw_exception(e); } } BOOST_ASSERT does not fit into the constexpr world at all, and neither does rangecheck. I could rewrite rangecheck so it could be constexpr, but only (I believe) by throwing the exception directly, rather than using boost::throw_exception. static void rangecheck (size_type i) { if (i >= size()) throw std::out_of_range e("array<>: index out of range"); } or even just: BOOST_CONSTEXPR const_reference at(size_type i) const { return i >= size () ? throw std::out_of_range e("array<>: index out of range") : elems[i]; } Has anyone put any effort into making Boost.Exception (and BOOST_ASSERT) work with constexpr? -- Marshall Marshall Clow Idio Software <mailto:mclow.lists@gmail.com> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait). -- Yu Suzuki

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Re: [boost] [mailman] trouble with list subscription
by Eric Niebler 10 Jan '13

10 Jan '13

Thanks for your timely response, DongInn. No worries, **it happens. Eric On 1/10/2013 11:47 AM, DongInn Kim wrote: > OK, guys. It seems to be back to normal. > > I am sorry for all the inconveniences and troubles with the mailman websites. > > Regards, > > -- > - DongInn > > On Jan 10, 2013, at 2:34 PM, Marshall Clow wrote: > >> >> On Jan 10, 2013, at 11:19 AM, DongInn Kim <dikim(a)cs.indiana.edu> wrote: >> >>> I am sorry for this. I am working on it. I will be back with you guys soon. >> >> Thank you! >> -- Marshall >> >>> On Jan 10, 2013, at 2:18 PM, Marshall Clow wrote: >>> >>>> I'm seeing this too >>>> -- Marshall >>>> >>>> >>>> Begin forwarded message: >>>> >>>>> From: Eric Niebler <eric(a)boostpro.com> >>>>> Subject: [boost] [mailman] trouble with list subscription >>>>> Date: January 10, 2013 10:46:39 AM PST >>>>> To: Boost mailing list <boost(a)lists.boost.org>, DongInn Kim <dikim(a)osl.iu.edu> >>>>> Reply-To: boost(a)lists.boost.org >>>>> >>>>> Many of the subscription links on >>>>> <http://www.boost.org/community/groups.html> are currently taking me to >>>>> a mailman error page. See for instance >>>>> <http://lists.boost.org/mailman/listinfo.cgi/boost>. I'm guessing this >>>>> has to do with the recent upgrade of the mailman software that DongInn >>>>> did. Does something need to change on the Indiana side, or are our links >>>>> out of date?

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[mailman] trouble with list subscription
by Eric Niebler 10 Jan '13

10 Jan '13

Many of the subscription links on <http://www.boost.org/community/groups.html> are currently taking me to a mailman error page. See for instance <http://lists.boost.org/mailman/listinfo.cgi/boost>. I'm guessing this has to do with the recent upgrade of the mailman software that DongInn did. Does something need to change on the Indiana side, or are our links out of date? -- Eric Niebler BoostPro Computing http://www.boostpro.com

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Re: [boost] [non-instrusive move] interest in new library?
by Joseph Gauterin 10 Jan '13

10 Jan '13

Out of curiosity, how are you detecting if a member function swap exists? >it detects at compile-time if the type of the >argument(s) has a member swap function In general, there's no way of knowing if a member swap function is more efficient than a single assignment. It isn't even for all the examples you gave - boost::array<T,N>::swap performs N boost::swaps, which, if T doesn't provide an efficient swap, results in N calls to std::swap, and 3*N assignments. In general I'm wary of using swap in a generic context unless the intent is to swap (i.e. not as a potential optimization of assignment). >The library is non-intrusive and generic, it will perform an efficient move >in terms of swap for any type providing a member >swap operation, e.g, std::vector, boost::array, user-defined types etc.

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Re: [boost] (Boost) QVM update
by Shakti Misra 09 Jan '13

09 Jan '13

Hi Emil, I also am waiting to try it out. My environment doesn't allow me to use boost completely. I may be getting little greedy, but any chance of using vectorization? :) ~Thanks Shakti On Wed, Jan 9, 2013 at 11:30 AM, Nathan Crookston < nathan.crookston(a)gmail.com> wrote: > Hi Emil, > > Emil Dotchevski wrote: > > > Boost QVM has been updated. Note, this library has not been reviewed > > yet and it is not part of Boost. > > > > Comments and bug reports are appreciated. > > > > I've been looking forward to this library. I often need something like > this in my work (mixture of graphics programming, image processing, and > geospatial applications). I wasn't happy with what ublas offered in the > static-sized 3-8 dimensions, so I rolled my own -- I'd be much happier to > have something like this, though. > > The documentation seem especially complete. A few questions and comments > that occurred to me as I was reading through (and occasionally glancing at > the code): > > * I'm sure [qvms]_traits is used all over the place, but I'd still rather > see scalar_traits, vector_traits, etc., especially as those may be > specialized by the user. > > * I thought s_traits was hard to find in the 'Generic programming > utilities' section. Should it be in the 'Type traits' section instead? > > * It looks like matrix types (probably vectors and quaternions too) must be > default constructible (for both make and the template conversion operator > of mat), though I didn't see that particular requirement noted -- am I > mistaken? > > * The SFINAE page seems to reference itself: > > sfinae > The boost::qvm::sfinae namespace contains only function names that use > SFINAE <circular link>. The boost::qvm namespace contains all Boost QVM > type and function names. > > I would have expected it to link to an explanation of sfinae -- not > necessarily part of QVM's docs. > > * inverse: I was surprised to see that you're inverting using the matrix > of cofactors. For my personal education, why do you use that method -- is > it more stable or efficient than others? A home-rolled implementation I > did something like the following: > > //Solving Ax = b > matrix<float> A; > vector<float> b; > inverse_matrix<float> inverse_m = invert(m);//actually perform lu > decomposition > vector<float> x = inverse_m * b;//actually back-substitutes from lu matrix. > > In that case, I knew that I'd only ever multiply by a vector -- which > allowed me to use a method which is at least as efficient as matrix > inversion and more numerically stable. I'm not sure if an inverse_matrix > type would allow something like: > > matrix<float> A = ...; > inverse_matrix<float> B = ...; > auto C = A * B; > auto D = B * A; > to be computed as efficiently as if B were really just a matrix type. I > could look that up tomorrow, when I have a reference on the material. If > it is, I think it would be interesting to have inverse return a view_proxy. > > * I haven't looked, but I assume QVM is targeting cases where both matrices > fit into cache? Meaning, it doesn't worry about things like cache > blocking? > > * I think the swizzling code is interesting. The Accessing * Elements > pages aren't too informative, though. It would help me if those pages, in > the 'See also:' section, were to link to examples of their usage. > > * Further on swizzling -- when I'm dealing with OpenGL texture coordinates, > the canonical names for them are s, t, r and q. Is there an interface > whereby I could allow writing something like this? > > TexCoord tc1(1, 2, 0, .5); > TexCoord tc2 = tc1 % TSRQ; > > I don't know that I'll ever need such a thing -- this is mostly out of > curiosity. > > I haven't had a chance to try QVM out -- I'd like to work up examples with > e.g., std::array<float,4>, then something with boost::units types as the > scalar types. In fact, working with the latter would be a killer feature > from this library for me. I'll let you know what I find. > > Thanks again for making this library available! > > Nate > > _______________________________________________ > Unsubscribe & other changes: > http://lists.boost.org/mailman/listinfo.cgi/boost >

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(Boost) QVM update
by Emil Dotchevski 09 Jan '13

09 Jan '13

Boost QVM has been updated. Note, this library has not been reviewed yet and it is not part of Boost. Boost QVM provides a set of generic functions for working with quaternions, and vector and matrix types of static size. All operations use a type-traits system, which enables types from other vector/matrix libraries to be integrated in a common type-safe interface. The current source code and documentation is available at http://www.revergestudios.com/boost-qvm. It contains minor bug fixes, and the following new features: - view proxies that negate matrix rows and columns (negr/negc) - view proxies that swap two rows or columns in a matrix (swapr/swapc) - functions for indexing at run-time of any vector or matrix object of arbitrary size. Comments and bug reports are appreciated. Thanks! Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode

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[non-instrusive move] interest in new library?
by THOMAS JORDAN 09 Jan '13

09 Jan '13

Apologies, my previous email I sent incomplete by mistake, please ignore that in favour of the following: Hi, Would there be interest for Boost in a small library providing a simple, non-instrusive emulation of basic move semantics for C++03 (though one which could also be used without harm in a C++11 environment)? The library currently consists of a small number of 'move' function overloads, plus a trait class. It can be used to facilitate move semantics/efficient value-orientated software design in environments which lack, or forbid C++11 or other, more intrusive C++03-aware move libraries (e.g., old/buggy compiler, learning curve prohibitive, etc.). In conjunction it facilitates/forces copy-elision and return-value (RVO) optimisations in certain situations where they might otherwise not be feasible. It works as follows: it detects at compile-time if the type of the argument(s) has a member swap function, and if so, it performs a swap, otherwise it calls the regular assignment operator ('move if possible, copy otherwise'). It can be used to provide an emulation of: - move-assignment between lvalues - moving an rvalue to an lvalue - moving an lvalue to a temporary It also supports moving between built-in arrays. Example use-cases are (ignoring namespace): #include "non_intrusive_move.h" //returning a value std::string foo(std::string s) { //e.g., append something to s //... //compiler can perform rvo (compiler would likely not perform nrvo if just used 'return s;') return move(s); } //moving a value to a function/ctor, when the value is not required by the calling code after the //function/ctor call std::string s("hello"); void bar(std::string s){...} bar(s); //copy bar(move(s)); //move //moving a value into place void MyClass::MyClass(std::string s) { //move value from s into default constructed member s_ move(s, s_); } Note that the combination of both moving a value to a function/ctor and then moving it into place e.g., std::string lv; //... MyClass mc(move(lv)); //lv no longer needed effectively results in a zero-copy invocation, with just a small number of fixed size swap, default ctor and shallow dtor calls, so this is pretty efficient. //moving a temporary into an lvalue std:: string lv; move(foo(), lv); //nicer than foo().swap(lv) The moved-from value is left in a 'valid' but undefined state, i.e., it can be destructed, assigned/moved to, swapped, etc. The library is non-intrusive and generic, it will perform an efficient move in terms of swap for any type providing a member swap operation, e.g, std::vector, boost::array, user-defined types etc. It also performs an efficient move for built-in arrays. The library is header-only and currently depends only on boost::enable_if and boost::swap as external dependencies. It is portable between C++03 and C++11 and has a gentle learning curve - the code is brief and easy to understand (with possible exception of the traits class) - I think that is quite an important feature of the library. It might be feasible to add a few other things, e.g., move, move_backward algorithms. The library is not intended to be standard-compliant (though similar where possible), and is not intended to compete with a much richer, but 'intrusive' library like Boost.Move. I've called it 'non-intrusive move' for the moment but it could of course be called something else (e.g., simple_move). Regards, Tom

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