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[gsoc] Interest in BGL v2?
by Michael Lopez 01 Apr '11

01 Apr '11

Hello all, My name is Michael and, if there is enough interest from the mailing list, I will be submitting an application for GSoC 2011 to work on the BGL v2. I have been working on a project called Origin ( http://code.google.com/p/origin/) when time permits, that houses the code that I intend to integrate into boost. The project was started by Andrew Sutton and I have taken an active role in its creation. The new library focuses on ease of use, replacement of property maps for labels, data structures with more concise and clear semantics, a new graph concept hierarchy, implementing graph algorithms to align with STL abstractions, and, finally, integrate C++0x into the BGL. I have already worked on the existing BGL back in 2009 for GSoC. While working on the BGL, I started seeing opportunities to bring the BGL more in-line with modern techniques and practices. I found that the library, though robust and quite mature, was lacking in some areas. The most unavoidable being C++0x support. The other design concern was that some of the data structures felt more like meta-programs. This is no good since a meta-program generates types that may model one of many concepts. Another feature that has been on BGL's want list is the implementation of algorithm objects. Some of the algorithm objects are already present in Origin. I realize that this is not a 3 month project. I fully understand that. However, I plan to continue maintaining this library in Origin, as I have been, until it is mature enough for a release and integration into other libraries. Hopefully there is enough interest to get this off of the ground. Please respond with your interests, questions and/or doubts. Michael Lopez

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[lexical-cast] version of lexical_cast in 1.46.1 is quite older than in trunk
by SergV 01 Apr '11

01 Apr '11

We discovered lexical_cast from 1.43 and 1.46.1 versions do not work in our program. But version of lexical_cast from trunk work very well. Version information: 1.46.1 - rev. 56161 13.09.2009 trunk - rev.65279 5.09.2010 1) Is there any reason that release does not include last version lexical_cast from trunk? 2) May be there are a lot of such forgotten files in trunk? Sergey Voropaev

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[MSM] feature request stop(const event& event_)
by Richard Szabo 01 Apr '11

01 Apr '11

Hi Christophe and all Now I have to put some effort to residing out code using MSM because one of our module where we use MSM has reached it's limits and we won't be able to compile it any more with VC9 32 bit compiler. In our implementation we have several sub state machines (around 20 per main state machine instance at the moment) ( nested in 4 level deep) and over time as we extend the functionality we introduce new sub state machines which are covering new functionality ... We now can not add any more new sub state machines because we can not compile any more :(. So I have decided to split the big state machines with a lot of subs state machines to stand alone small state machine instances and use our dispatching framework to dispatch events between them. This way I will get small compile units. I'm managed to complete a job apart form one problem I have now. I'm not able to generally trigger the exit functions on the current active states of a state machine when it is finished it's execution like when a sub state machine exists to the outer state machine. Is it possible to implement something like stop method on the back end which would call exit on each region current state and than an exit of the state machine whit an event passed as an argument. ? this would help me a lot and it would be similar to the start. other minor thing is it possible to make public this version of start methode in the back_end ? template <class Event> void start(Event const& incomingEvent) Br. Richard

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Re: [boost] [submission] STL-compliant containers with copy-on-write
by Alexandr Sterligov 01 Apr '11

01 Apr '11

I'm working with embedded software and we have to use COW containers pretty often. I haven't found any COW container implementation which may replace STL containers and had to implemented it. It is not possible to make STL containers with COW keeping all semantics of the STL containers. For example, almost any member-function may throw, because copy ctor may throw. It is not always safe to replace std::vector with mine cow_vector, but in most cases it is safe. For example, it is not safe if you have saved constant pointer or constant reference from constant cow_vector. But with std::vector saving addresses is not a good idea as well, because resize, push_back and others may cause address change. In my implementation iterators are safe, for example: cow_vector<int> a; a.push_back( 1 ); cow_vector<int> b; b.push_back( 2 ); cow_vector<int>::const_iterator itA = a.begin(); assert( *itA == 1 ); cow_vector<int>::const_iterator itB = b.begin(); assert( *itB == 2 ); b = a; assert( itA == a.begin() ); assert( itB == b.begin() ); assert( *itA == 1 ); assert( *itB == 1 ); a[0] = 3; // or *a.begin() = 3 assert( itA == a.begin() ); assert( itB == b.begin() ); assert( *itA == 3 ); assert( *itB == 1 ); You example: int* p = &v[1]; // copying is done here v[0] = 1; assert( p == &v[1] ); // still valid as copying was done before. But in following case it won't work now: void test( const cow_vector<int>& a ) { const int *a = &v[1]; v[0] = 1; assert( p != &v[1] ); // sorry, another pointer if internal buffer was shared. } Please note, that it's possible to do copying if any reference or pointer is taken from iterator or container itself, but my current implementation doesn't do it. That's easy to change. > IMO it isn't possible to really make that work anyway since STL > containers expose references to their elements *and* make guarantees > about iterator stability and element layout. For example, if v is a > vector and I do > > v[0] = 1; > > it's not allowed to change the address of v[1] > -- > Dave Abrahams > BoostPro Computing > http://www.boostpro.com ---- Best regards, Alexander Sterligov

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GSOC2011 (Introduction)
by Harinderpal Singh 01 Apr '11

01 Apr '11

Hi My name is Harinderpal Singh. I am from Lovely Professional University, Punjab, India. I am a fourth year B.Tech student. I have worked on c++. I also have basic knowledge of Mysql. I have competed in various inter college level competitions. I work on linux(ubuntu) and also have knowledge of windows. I don't have any experience with open source previously.I am interested in Checks & Hashes module Regards Harinderpal Singh Website; http://www.iyouth.in Blog: http://codelinguist.wordpress.com/ <http://codelinguist.wordpress.com/> +91-9888573505

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boost interprocess (>1.45) robust mutexes
by Rusk . 31 Mar '11

31 Mar '11

Hi, I have noticed that in version 1.45 Ion Gaztanaga has added detail/robust_emulation.hpp which contains code that seems to emulate pthread_mutexattr_setrobust_np(). I understand this may be needed for platforms that don't support robust mutexes. My version of linux does seem to support robust mutexes, however I could not find a way to compile or in any other way to use this flag on posix mutexes in boost 1.46.1. Article here ( http://stackoverflow.com/questions/1179685/how-do-i-take-ownership-of-an-ab…) indicates the way to do this. But now emulation for robust mutexes has been added I wonder if I am missing something. Thanks, ddrum

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GSoC idea
by Brestin Seby 31 Mar '11

31 Mar '11

Hello, my name is Sebastian Brestin. I am a student from Romania and I am really looking forward to working for C++ Boost library. I have noticed that in the past years Boost has proposed many times on building a library for operations on Big Integers, yet I do not find any implementation in boost_1_46_1 . Also I have noticed that many students choose Java over C++ in algorithm contests, because Java has a built-in library that permits operations on Big Numbers. As I have seen that so far neither STL, nor Boost have implemented operations over Big Numbers, I suggest to implement those operations over Big Numbers: - addition, subtraction, multiplication, division, modulo, comparison, factorial, radical etc. - conversion from one base representation to another( for example from decimal to hexadecimal, or from decimal to binary, or even in other bases) - operations in modulo classes. - those operations will not be limited only to integer numbers but also extended to floating point numbers in simple precision and double precision as well( except modulo classes). I think that this library could help not just students, but it can be also used in finding large prime numbers for security keys, why not ( using the "sieve of eratostene" on those large numbers). Thank you for your time and I hope I will get some feed back over this idea.

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Algebraic abstractions related to (big) integers in C++
by Thomas Klimpel 31 Mar '11

31 Mar '11

Dear (big) integer enthusiasts, The goal of this message is to reflect on the two's complement representation of negative integers, from a relatively abstract algebraic perspective. Some of the questions that arise in this context are whether the two's complement representation would be well suited for (i) a fixed width integer data type (ii) a fixed point number data type (iii) a variable width integer data type (iv) a floating point number data type Circumstantial evidence suggests that it's well suited for (i) and (ii), but not well suited for (iv). The following quote from Bill Gosper (1972) "By this strategy, consider the universe, or, more precisely, algebra [...] therefore algebra is run on a machine (the universe) which is twos-complement." (<http://www.inwap.com/pdp10/hbaker/hakmem/hacks.html#item154>) could be seen as evidence in favor of using two's complement representation for (iii). However, XInt and other bigint libraries took the opposite decision, so there is strong circumstantial evidence against using two's complement representation for (iii). Let me start with a disclaimer that I'm not an expert in algebra. The following thoughts emerged when I tried to understand the semi-direct product. I wanted to see how it works for a concrete "small" group. So I tried to write the Quaternion group (the one with the 8 elements 1, -1, i, -i, j, -j, k, -k) as a semi-direct product. This didn't work, because the Quaternion group is not a semi-direct product. But after some time I managed to "decompose" the Quaternion group into abelian groups in a different way. I subsequently learned that this sort of problem is called the group extension problem <http://en.wikipedia.org/wiki/Group_extension>. It's a solved problem, but I would have to learn some homological algebra to understand its solution. Let's look at the "ring of integers" (denoted by "Z") and the "ring of integers modulo m" (denoted by "Z_m"). We want to "approximate" the "ring of integers" by the "ring of integers modulo m". One of the advantages of this approach is that it's relatively easy to represent the "ring of integers modulo m" in a computer, especially for "m = 2^n" (more concretely "m = 2^32" for int32_t and "m = 2^64" for int64_t). There exists exactly one non-trivial ring homomorphism "p : Z -> Z_m" from the "ring of integers" into the "ring of integers modulo m". (The integer "1" is mapped to the corresponding "1", and the additive group of the "ring of integers modulo m" is generated by "1".) A good way to describe how we "approximate" "Z" by "Z_m" is to define a map "q : Z_m -> Z" such that "p(q(i)) = i for all i". Because the map "q" is not uniquely determined by the condition "p(q(i))=i", let's add the additional constraint "-m/2 <= q(i) < m/2". It's easily checked that this uniquely determines the map "q". This map "q" is not a ring homomorphism, but that's OK as there does not exists any non-trivial ring homomorphism from "Z_m" into "Z". Still we should try to measure the deviation of "q" from a ring homomorphism by taking a look at "S(a, b) := q(a) + q(b) - q(a + b)" and "P(a, b) := q(a) q(b) - q(a b)". It's easily checked that "p(S(a, b)) = 0" and "p(P(a, b)) = 0". This shows that "S(a, b)" and "P(a, b)" are multiples of "m". A quick estimation shows "-1 <= S(a, b)/m <= 1" and "-(m+1)/4 < P(a, b)/m <= (m+2)/4". This doesn't look too bad, but still bad enough to question whether the constraint "-m/2 <= q(i) < m/2" is really the way to go. Instead of the constraint "-m/2 <= q(i) < m/2", we could have also used the constraint "0 <= q(i) < m" or the constraint "-m/2 < q(i) <= m/2". One reason to prefer the constraint "-m/2 <= q(i) < m/2" over the constraint "-m/2 < q(i) <= m/2" is that we exactly get the two's complement representation of signed integers for "m = 2^n", which was the very reason that we investigated these algebraic relations in the first place. It's also more consistent with the "a <= x < b" representation of ranges so typical for C/C++. I want to give a third reason why the constraint "-m/2 <= q(i) < m/2" should be preferred over the constraint "-m/2 < q(i) <= m/2". Let's define a "round to nearest" division and the corresponding modulo operation for the "ring of integers" by "rdiv(a, b) := floor(1/2 + a/b)" and "rmod(a, b) := a - b rdiv(a, b)". It's easily checked that "-m/2 <= rmod(i, m) < m/2". It could be objected that implementing "round to nearest" by "i = floor(0.5 + x);" is only correct for non-negative values of "x". The correct implementation of "round to nearest" seems to be "i = x >= 0 ? floor(x + 0.5) : ceil(x - 0.5);". But I don't think that the more complicated definition of "round to nearest" is always "more" correct than the simpler one. At least when manipulating polygons, there can be situations where the simpler definition turns out to be the "more" correct one. But let's investigate to constraint "0 <= q(i) < m" now. A quick estimation shows "0 <= S(a, b)/m <= 1" and "0 <= P(a, b)/m < m-1". So "S(a, b)/m" could be stored in a single "carry bit" and "P(a, b)/m" can be stored as a value of "Z_m". It is therefore not uncommon to have access to "S(a, b)/m" in machine language via a "carry bit" and to "P(a, b)/m" by using a machine instruction that computes "a b" and "P(a, b)/m" at the same time and stores "a b" and "P(a, b)" in different registers. (My experiences with machine language are from the time before 1996, so pardon me if these statement should not be fully correct.) The statement about the carry bit is not fully correct, because the carry bit is normally not just a result of an addition in machine language, but is also taken into account during the addition. So if "c" is the carry bit before the addition, the addition will return the value "p(c) + a + b" in "Z_m" and the new carry bit "(c + q(a) + q(b) - q(p(c) + a + b))/m". It's probably even possible to write this "add_with_carry" operation as a function in C or as a template in C++. But I don't really believe that many compilers will notice the equivalence between a template like the following and the "add_with_carry" machine instruction. template <Uint> typename boost::enable_if<boost::is_unsigned<Uint>, bool>::type add_with_carry(Uint& a, const Uint& b, bool c) { a += (c != 0); a += b; return (c != 0) ? (a <= b) : (a < b); } And I'm pretty certain that there doesn't exist any compiler will notice the equivalence between a template like the following and the mentioned machine instruction for a multiplication returning the complete result. I'm not even certain myself that they are equivalent (but I could write a test to verify it for me, if I really wanted to be certain). template <Uint> typename boost::enable_if<boost::is_unsigned<Uint>, Uint>::type multiply_full_result(Uint& a, const Uint& b) { Uint upper_a = (a >> (sizeof(Unit)/2)); Uint upper_b = (b >> (sizeof(Unit)/2)); Uint lower_a = a & (Uint(-1) >> (sizeof(Unit)/2)); Uint lower_b = b & (Uint(-1) >> (sizeof(Unit)/2)); Uint upper = upper_a * upper_b; upper += ((upper_a*lower_b) >> (sizeof(Unit)/2)); upper += ((lower_a*upper_b) >> (sizeof(Unit)/2)); a *= b; return upper; } I'm starting to get problems with the length of this message now, because it is quite reasonable to expect that the number of people that will even try to read the message gets lower and lower as the message gets longer and longer. And this is already my third start from scratch trying to come up with something reasonable in size and readability. My first attempt directly started with p-adic numbers and p-adic integers, then tried to explain how the two's complement representation is related to 2-adic integers. It noted that it is indeed an approximation in the 2-adic metric, but this normally doesn't buy us anything, because the 2-adic metric is almost never the relevant metric for our problem domain at hand. This is also one of the reasons why the two's complement representation should be avoided for floating point numbers, because the relevant metric in this case is the normal metric of the real numbers. My second attempt tried to take the opposite approach, and started with the C++ statement "std::size_t n = std::max(1, c.size());", noting that it will provoke a compile error. After some discussion and additional examples like the expressions "c.size()/-2" and "-c.size()/2", it claimed that Haskell was able to solve these problems by not assigning any concrete type to "2" at all, but just the abstract "Num" typeclass. One part of the problems that are meant here is described in the following statement: "What I consider especially strange from an algebraic point of view, is to automatically promote a signed integer type to its corresponding unsigned integer type, when an arithmetic expression contains both signed and unsigned integer types. Shouldn't it be the other way round? Or wouldn't it be even better, if there would be no automatic conversion at all? At least from an algebraic point of view, any natural number is also an integer, not vice versa like in C." So let's try to come to some sort of conclusion now, even so not all semantical issues I wanted to discuss have been raised, and nearly no solutions for the raised issues have been presented. It looks to me now like it can be advantageous to implement operations for signed (variable or fixed width) integer data types in terms of operations for unsigned integer data types. This can be done independent of whether the two's complement representation is used or not. However, we should still be careful to provide the correct semantic for signed integer types, even if we implement them in terms of unsigned integer types. It is a questionable design when the TTMath bignum library lets it signed integer type derive public from its unsigned integer type ("template<uint value_size> class Int : public UInt<value_size> { ... };"), because the relationship between signed and unsigned integer types is not a "is a" relationship as required for public inheritance. (Think about it, a signed integer is really not an unsigned integer, even if the unsigned integer type would model the "ring of integers modulo m" instead of the "natural numbers".) Is is also questionable when a relatively new language like the D programming language cripples its "Usual Arithmetic Conversions" by stating "The signed type is converted to the unsigned type." as rule 4.4. Even so it is true that an integer can be converted to an "integer modulo m" (remember the ring homomorphism "p : Z -> Z_m"), are there really good reasons to apply such a conversion automatically? For the C/C++ language, the answer is definitively yes: "backward compatibility". But I don't think that this reason would have applied to D. And please pardon me if I imply press the send button now. Regards, Thomas

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[context review] Review is finished
by Vicente BOTET 31 Mar '11

31 Mar '11

Hi all, As there were no request to extend the review, the review of Oliver Kowalke Context library is finished. I think that even if there were not too much review and discussions, there were enough material to make Boost.Context a library having the Boost level. I hope I could be able to give the review result soon. I would like to thank Oliver and of course all the reviewers for their participation I'm afraid there was some problems with User ML. If you think that you could made a review next weekend, please don't hesitate to send it to the Dev ML. Vicente, Review manager

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gsoc project(checks)
by Александр 31 Mar '11

31 Mar '11

Hello, Paul. Here i send you test message. Also i send you two different messages, one with .zip file and one with .rar. Actually, here i want to say few things i thought about after i finished coding. I made my class working with uint8_t type - byte arrays. But then i thought it should be working the same way with any int type actually.. And even with any data if we think of it as a simple sequence of bytes. But here i came to the problem: 1. i can replace uint8_t by template class and then use cast in process() method to get data in byte representation: byte *bytes = reinterpet_cast<byte*>(&in_data) and then just deal with byte sequence. 2. or remove vector from member and treat any structure as sequence of bytes. But the thing is - we need checksum for data stored in structure of checksum for structure itself? Because if we take complex structure(something like map<pair<set<int>,pair<int,string> > >) what checksum are we calculating actually? Thank you! -- Alexandr mailto:daywalker@mail333.com

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