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  • fast algorithm to sort very small set

    - by aaa
    hello. This is the problem I ran into long time ago. I thought I may ask your for your ideas. assume I have very small set of numbers (integers), 4 or 8 elements, that need to be sorted, fast. what would be the best approach/algorithm? my approach was to use the max/min functions only. At this point it becomes somewhat hardware dependent , so let us assume Intel 64-bit processor with SSE3 . Thanks

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  • custom C++ boost::lambda expression help

    - by aaa
    hello. A little bit of background: I have some strange multiple nested loops which I converted to flat work queue (basically collapse single index loops to single multi-index loop). right now each loop is hand coded. I am trying to generalized approach to work with any bounds using lambda expressions: For example: // RANGE(i,I,N) is basically a macro to generate `int i = I; i < N; ++i ` // for (RANGE(lb, N)) { // for (RANGE(jb, N)) { // for (RANGE(kb, max(lb, jb), N)) { // for (RANGE(ib, jb, kb+1)) { // is equivalent to something like (overload , to produce range) flat<1, 3, 2, 4>((_2, _3+1), (max(_4,_3), N), N, N) the internals of flat are something like: template<size_t I1, size_t I2, ..., class L1_, class L2, ..._> boost::array<int,4> flat(L1_ L1, L2_ L2, ...){ //boost::array<int,4> current; class variable bool advance; L2_ l2 = L2.bind(current); // bind current value to lambda { L1_ l1 = L1.bind(current); //bind current value to innermost lambda l1.next(); advance = !(l1 < l1.upper()); // some internal logic if (advance) { l2.next(); current[0] = l1.lower(); } } //..., } my question is, can you give me some ideas how to write lambda (derived from boost) which can be bound to index array reference to return upper, lower bounds according to lambda expression? thank you much

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  • C++ boost::lambda::ret equivalent in phoenix

    - by aaa
    hello. Boost lambda allows to overwrite deduced return type using ret<T> template. I have tried searching for equivalent in phoenix but could not find one. Is there an equivalent in phoenix? I know how to make my own Replacement but I would rather not. thank you

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  • elisp macro to write function?

    - by aaa
    hello I have written few functions, which nearly identical, save for names. For example ; x is name, such as function/paragraph/line/etc. (defun my-x-function (interactive) (mark-x) (do-more-stuff) (modify-x)) is there a way to put it automatically? I have a feeling this is what macros do, but I am not sure how to use them. you help/maybe small example would be great Thanks

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  • given two bits in a set of four, fine position of two other bits

    - by aaa
    hello I am working on a simple combinatorics part, and found that I need to recover position of two bits given position of other two bits in 4-bits srring. for example, (0,1) maps to (2,3), (0,2) to (1,3), etc. for a total of six combinations. My solution is to test bits using four nested ternary operators: ab is a four bit string, with two bits set. c = ((((ab & 1) ? (((ab & 2) ? ... ))) : 0) abc = ab | c recover the last bit in the same fashion from abc. can you think of a better way/more clever way? thanks

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  • C++ template name pretty print

    - by aaa
    hello. I have need to print indented template names for debugging purposes. For example, instead of single-line, I would like to indent name like this: boost::phoenix::actor< boost::phoenix::composite< boost::phoenix::less_eval, boost::fusion::vector< boost::phoenix::argument<0>, boost::phoenix::argument<1>, I started writing my own but is getting to be complicated. Is there an existing solution? if there is not one, can you help me to finish up my implementation? I will post it if so. Thanks

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  • Fast modulo 3 or division algorithm?

    - by aaa
    Hello is there a fast algorithm, similar to power of 2, which can be used with 3, i.e. n%3. Perhaps something that uses the fact that if sum of digits is divisible by three, then the number is also divisible. This leads to a next question. What is the fast way to add digits in a number? I.e. 37 - 3 +7 - 10 I am looking for something that does not have conditionals as those tend to inhibit vectorization thanks

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  • C++, throw exception from initializer list

    - by aaa
    hello. what is the best way to throw exception from initializer list? for example: class C { T0 t0; // can be either valid or invalid, but does not throw directly T1 t1; // heavy object, do not construct if t0 is invalid, by throwing before C(int n) : t0(n), // throw exception if t0(n) is not valid t1() {} }; I thought maybe making wrapper, e.g. t0(throw_if_invalid(n)). What is the practice to handle such cases? Thanks

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  • integer division properties

    - by aaa
    hi. does the following integer arithmetic property hold? (m/n)/l == m/(n*l) At first I thought I knew answer (does not hold), but now am not sure. Does it hold for all numbers or only for certain conditions, i.e. n > l?

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  • fast algorithm implementation to sort very small set

    - by aaa
    hello. This is the problem I ran into long time ago. I thought I may ask your for your ideas. assume I have very small set of numbers (integers), 4 or 8 elements, that need to be sorted, fast. what would be the best approach/algorithm? my approach was to use the max/min functions. I guess my question pertains more to implementation, rather than type of algorithm. At this point it becomes somewhat hardware dependent , so let us assume Intel 64-bit processor with SSE3 . Thanks

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  • 3d symmetry search algorithm

    - by aaa
    this may be more appropriate for math overflow, but nevertheless: Given 3d structure (for example molecule), what is a good approach/algorithm to find symmetry (rotational/reflection/inversion/etc.)? I came up with brute force naive algorithm, but it seems there should be better approach. I am not so much interested in genetic algorithms as I would like best symmetry rather then almost the best symmetry link to website/paper would be great. thanks

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  • How to obtain the native stacktrace from native exceptions caught in managed code

    - by aaa
    I have some managed code that calls to a method inside some native DLL(i have the appropriate symbol files). Sometimes, that native method throws an exception which I catch in my managed code. However, when i print the stacktrace from my caught exception, I see only managed code (the last frame is the call to the native code .. but it don't see the stacktrack within the native code). How can I obtain the native callstack as well? *When i'm debugging the code, i am able to step into the native code, and see the actuall call stack.

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  • computing hash values, integral types versus struct/class

    - by aaa
    hello I would like to know if there is a difference in speed between computing hash value (for example std::map key) of primitive integral type, such as int64_t and pod type, for example struct { int16_t v[4]; };. I know this is going to implementation specific, so my question ultimately pertains to gnu standard library. Thanks

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  • optimal memory layout for read-only/write memory segments.

    - by aaa
    hello. Suppose I have two memory segments (equal size each, approximately 1kb in size) , one is read-only (after initialization), and other is read/write. what is the best layout in memory for such segments in terms of memory performance? one allocation, contiguous segments or two allocations (in general not contiguous). my primary architecture is linux Intel 64-bit. my feeling is former (cache friendlier) case is better. is there circumstances, where second layout is preferred? Thanks

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  • C/C++ packing signed char into int

    - by aaa
    hello I have need to pack four signed bytes into 32-bit integral type. this is what I came up to: int byte(char c) { return (unsigned char)c; } int pack(char c0, char c1, ...) { return byte(c0) | byte(c1) << 8 | ...; } is this a good solution? Is it portable? is there a ready-made solution, perhaps boost? Thanks

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  • Faster integer division when denominator is known?

    - by aaa
    hi I am working on GPU device which has very high division integer latency, several hundred cycles. I am looking to optimize divisions. All divisions by denominator which is in a set { 1,3,6,10 }, however numerator is a runtime positive value, roughly 32000 or less. due to memory constraints, lookup table is not option. Can you think of alternatives? I have thought of computing float point inverses, and using those to multiply numerator. Thanks

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  • x86-64 long double precision

    - by aaa
    hello. What is the actual precision of long double on Intel 64-bit platforms? is it 80 bits padded to 128 or actual 128 bit? if former, besides going gmp, is there another option to achieve true 128 precision?

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  • C/C++ include file order/best practices

    - by aaa
    Hello. Is there recommended order in which include files should be specified? For example, the system files, STL, Boost, go before of after local include files? is there a particular reason to choose one or another? Thanks

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  • Porting SHA512 Javascript implemention to Actionscript

    - by AAA
    Hello Everyone, I am wondering if anyone can help me in porting a SHA-512 implemention in Javascript to Actionscript. Since both Javascript and Actionscript share the same origin, I think porting it will be easy for people who are used to Actionscript. The code for sha512 in javascript can be found here: http://pajhome.org.uk/crypt/md5/sha512.html Thank you.

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  • curious ill conditioned numerical problem

    - by aaa
    hello. somebody today showed me this curious ill conditioned problem (apparently pretty famous), which looks relatively simple ƒ = (333.75 - a^2)b^6 + a^2 (11a^2 b^2 - 121b^4 - 2) + 5.5b^8 + a/(2^b) where a = 77617 and b = 33096 can you determine correct answer?

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  • gcc memory alignment pragma

    - by aaa
    hello. Does gcc have memory alignment pragma, akin #pragma vector aligned in Intel compiler? I would like to tell compiler to optimize particular loop using aligned loads/store instructions. Thanks

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