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[crc] Simple example please
by Vladimir Prus 10 Jun '03

10 Jun '03

Hi Alex, > I'd like to calculate a value for a cyclic redundancy check (crc) for a > number of files. > > This isn't going to be transmitted anywhere, I simply want to compare the > values to see whether the files are exactly the same. I know I can simply > check byte for byte, but I've got a few thousand files and it's easier to > calculate the crc for each and see whether any are the same first. Here's the function that I use for the same purpose. Might not be optimal, but works: unsigned file_crc(const string& name) { #if defined(__GNUC__) && __GNUC__ < 3 ifstream ifs(name.c_str(), ios::binary); #else ifstream ifs(name.c_str(), ios_base::binary); #endif if (!ifs) return 0; else { using namespace boost; crc_32_type crc32; int c; while( (c = ifs.rdbuf()->sbumpc()) != -1) crc32.process_byte(char(c)); return crc32.checksum(); } } I believe some example of this kind should be included... Daryle, what do you think? HTH, Volodya

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Lapack for uBlas
by Achim Domma 10 Jun '03

10 Jun '03

Hi, does somebody know a Lapack implementation which can be used with uBlas? I need a solver for an linear equation system and would prefer to not rewrite it by hand. Achim

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vector ranges
by cerenoc 10 Jun '03

10 Jun '03

Hello, I just wanted to clarify if the following behavior is correct. As far as I understood, in matrix and vector range function, the 1st argument defines the starting point and the second defines the length of the range. The following code I ran on gcc 2.96 shows that the behavior is different when starting at 0 and starting somewhere else. Is this a bug, or am I misunderstanding something? Thank you, Julian // define some vector r(3) std::cout << r << "\n\n"; boost::numeric::ublas::vector<double> rr = r(range(0, 0)); std::cout << rr << "\n\n"; rr = r(range(0, 1)); std::cout << rr << "\n\n"; rr = r(range(0, 2)); std::cout << rr << "\n\n"; rr = r(range(0, 3)); std::cout << rr << "\n\n"; //rr = r(range(1, 0)); // THIS RESULTS IN ASSERTION ERROR //std::cout << rr << "\n\n"; rr = r(range(1, 1)); std::cout << rr << "\n\n"; rr = r(range(1, 2)); std::cout << rr << "\n\n"; rr = r(range(1, 3)); std::cout << rr << "\n\n"; OUTPUT: [3](0,1,2) [0]() [1](0) [2](0,1) [3](0,1,2) [0]() [1](1) [2](1,2)

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confused by matrix assignment
by cerenoc 10 Jun '03

10 Jun '03

Hi, I'm sorry I am new to this and also not up on the math notation you guys are using. I am confused by the definitions of slices and strides. I am trying to perform a reasonably simple operation of e.g. assigning a vector v(2) to a (sub)matrix m(3,3). In matlab notation, for instance: m = 0 1 2 3 4 5 6 7 8 v = 15 16 m(2, 1:2) = v Resulting in m = 0 1 2 15 16 5 6 7 8 What is the best way to do this with uBLAS? Thank you very much Julian

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RE: [Boost-Users] Re: Tree Object Needed!
by Jim.Hyslop 09 Jun '03

09 Jun '03

Hossein Haeri wrote: > Does the method you mentioned work for my problem in > which there is no ordering? If yes, please explain it > in more detail (with an example). Trees are generally used with ordered sequences, aren't they? If your data are not ordered, then how do you propose to insert them into the tree? What, well, order would they appear in the tree? If you provide a little more information about the problem domain, we can help you figure out the best container to use. -- Jim

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RE: [Boost-Users] Re: Tree Object Needed!
by Mark Storer 09 Jun '03

09 Jun '03

I don't mean to come off like a hard case, and I may well be wrong but... This whole line of questioning has that "homework assignment" smell to it. The initial question was _highly_ school-related: > I need to have some template doing the jobs of an > ordinary BST (Binary Search Tree). Nothing that fancy, > but something at the level we all have been educated > in CS1/FCS1, or similar courses. Does boosts > repository contain such an object? The utter lack of background detail leads me to believe that this is just a toy problem... a homework assignment. And then there's the yahoo email address... most proffesional programmers have @mybusiness addresses, though that doesn't mean everyone here is a proffesional. Oh, and the final bit of oddness: > Why don't I write it myself? Simply, because I want to > optimise the time! How is waiting a week or so for some mailing list to hand you an answer "optimizing the time"? This has just been bothering me, I felt the need to speak out. If I'm wrong, then I offer my heartfelt appoligies. This may be what Mr. Hyslop was trying to dig at, I'm just not a patient or subtle person. And I don't mind appologizing for my mistakes (lots of practice, as you might imaging with this sort of behavior). --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typdef std::disclaimer<Cardiff> Discard;

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Threads Library
by Brian Plummer 09 Jun '03

09 Jun '03

Atomic operations (atomic_add, atomic_subtract etc) are not handled in the Boost Threads library. My guess is that this is because this cannot be accomplished, based on what I know about this topic (which isn't too much), in a portable way. Is this the reason? If not, having these operations in the Threads library would be a big benefit. Thanks, Brian

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counted_base vs. sp_counted_base - boost 1.30.0 functionality deprecated
by Anders Hybertz 09 Jun '03

09 Jun '03

Hi Up to and including version 1.29.0 of the boost library I had an object which inherited from boost::counted_base, and could actually within that object control when it should be deleted. The object spawned a thread which was listening on a queue, when there was pushed an shutdown message on the queue, I could safely delete the object. In boost 1.30.0 the counted_base changed name and namespace to boost::detail::sp_counted_base, but the way it works also changed - so now my object's destructor is called whenever it's going out of scope - which I don't want. Any ideas - or should I provide a small sandbox example Thanks in advance Anders Hybertz

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[crc] Simple example please
by Alex Henderson 09 Jun '03

09 Jun '03

Hi, I'd like to calculate a value for a cyclic redundancy check (crc) for a number of files. This isn't going to be transmitted anywhere, I simply want to compare the values to see whether the files are exactly the same. I know I can simply check byte for byte, but I've got a few thousand files and it's easier to calculate the crc for each and see whether any are the same first. I've looked at the crc library, but can't get my head round the example. It seems to test the library rather than show how its used. I'm after something like std::vector<char> MyStream1; // the whole file (about 500kb) boost::SomeCRCTypeThatIsOptimisedForSafetyAndLargeishBlocks<???> x; long = x.checkme(MyStream1); Could someone please point me to some code where a simple example is detailed? Thanks, Alex

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confused by ublas submatrix assignment
by cerenoc 08 Jun '03

08 Jun '03

Hi, I am new to this and am confused by the (sub)matrix operations and also not up on the math nomenclature this group is using such as slices and strides. I am trying a reasonably simple operation of assigning a vector v(2) to a submatrix (3,3). For example, in matlab notation: m = 0 1 2 3 4 5 6 7 8 v = 15 16 m(2, 1:2) = v resulting in: m = 0 1 2 15 16 5 6 7 8 What is the best way to do this with ublas? I suppose I need to convert the vector into another type first, but which one - a slice, a range? I tried both with no success. Thanks a lot, Julian

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