bitset

Why does std::bitset expose bits in little-endian fashion?

由 痴心易碎 提交于 2019-11-27 04:51:26
问题 When I use std::bitset<N>::bitset( unsigned long long ) this constructs a bitset and when I access it via the operator[] , the bits seems to be ordered in the little-endian fashion. Example: std::bitset<4> b(3ULL); std::cout << b[0] << b[1] << b[2] << b[3]; prints 1100 instead of 0011 i.e. the ending (or LSB) is at the little (lower) address, index 0. Looking up the standard, it says initializing the first M bit positions to the corresponding bit values in val Programmers naturally think of

Large (0,1) matrix multiplication using bitwise AND and popcount instead of actual int or float multiplies?

由 一曲冷凌霜 提交于 2019-11-27 04:42:33
问题 For multiplying large binary matrices (10Kx20K), what I usually to do is to convert the matrices to float ones and perform float matrix multiplication as integer matrix multiplication is pretty slow (have a look at here). This time though, I'd need to perform over hundred thousands of these multiplications and even a millisecond performance improvement on average matters to me . I want an int or float matrix as a result, because the product may have elements that aren't 0 or 1. The input

Java BitSet Example

由 情到浓时终转凉″ 提交于 2019-11-26 23:59:11
I'm looking for a good Java BitSet example to work with 0 and 1s. I tried looking at the Javadocs but I don't understand the usage of the class by just reading that. For instance, how would the and , or , and xor methods work on two different BitSet objects? For example: BitSet bits1 = new BitSet(); BitSet bits2 = new BitSet(); bits2.set(1000001); bits1.set(1111111); bits2.and(bits1); System.out.println(bits2); If I do this it returns bits2 as empty why is that? For the specific problem you mentioned: when you called bits2.set(1000001) , you set the one millionth and first bit to true. Then

Convert Byte Array into Bitset

由 三世轮回 提交于 2019-11-26 23:11:40
问题 I have a byte array generated by a random number generator. I want to put this into the STL bitset. Unfortunately, it looks like Bitset only supports the following constructors: A string of 1's and 0's like "10101011" An unsigned long. (my byte array will be longer) The only solution I can think of now is to read the byte array bit by bit and make a string of 1's and 0's. Does anyone have a more efficient solution? 回答1: Something like this? (Not sure if template magic works here as I'd expect

Auto increment in MongoDB to store sequence of Unique User ID

由 倾然丶 夕夏残阳落幕 提交于 2019-11-26 17:52:32
I am making a analytics system, the API call would provide a Unique User ID, but it's not in sequence and too sparse. I need to give each Unique User ID an auto increment id to mark a analytics datapoint in a bitarray/bitset. So the first user encounters would corresponding to the first bit of the bitarray, second user would be the second bit in the bitarray, etc. So is there a solid and fast way to generate incremental Unique User IDs in MongoDB? Konstantin Pribluda You can, but you should not https://web.archive.org/web/20151009224806/http://docs.mongodb.org/manual/tutorial/create-an-auto

BitSet to and from integer/long

由 我们两清 提交于 2019-11-26 15:26:39
If I have an integer that I'd like to perform bit manipulation on, how can I load it into a java.util.BitSet ? How can I convert it back to an int or long? I'm not so concerned about the size of the BitSet -- it will always be 32 or 64 bits long. I'd just like to use the set() , clear() , nextSetBit() , and nextClearBit() methods rather than bitwise operators, but I can't find an easy way to initialize a bit set with a numeric type. The following code creates a bit set from a long value and vice versa: public class Bits { public static BitSet convert(long value) { BitSet bits = new BitSet();

Define bitset size at initialization?

由 久未见 提交于 2019-11-26 11:24:12
I want to make a bitset in C++. I did a bit of research. All examples I found where like this: bitset<6> myBitset; // do something with it But I don't know the size of the bitset when I define the variable in my class: #include <bitset> class Test { public: std::bitset *myBitset; } This won't compile... And initializing like this also doesn't work: int size = getDependentSizeForBitset(); myBitset = new bitset<size>(); Boost has a dynamic_bitset you can use. Alternatively, you can use a vector<bool> , which (unfortunately) is specialized to act as a bitset. This causes a lot of confusion, and

How to implement a bitset in C?

由 不羁的心 提交于 2019-11-26 11:03:39
问题 I have been using the Bitset class in Java and I would like to do something similar in C. I suppose I would have to do it manually as most stuff in C. What would be an efficient way to implement? byte bitset[] maybe bool bitset[] ? 回答1: CCAN has a bitset implementation you can use: http://ccan.ozlabs.org/info/jbitset.html But if you do end up implementing it yourself (for instance if you don't like the dependencies on that package), you should use an array of ints and use the native size of

Is the use of std::vector<bool> objects in C++ acceptable, or should I use an alternative?

由 我的梦境 提交于 2019-11-26 09:50:25
问题 I\'m working with a user-defined quantity of bits (I\'m holding a three-dimensional array of bits, so the size increases cubically - assume no less then 512 bits), and need to flip them each individually. Right now, just on a computer, I\'m using the bool type, since memory isn\'t an issue. I do plan to move the code to a microcontroller in the future, and so processing power and memory requirements may be an issue. Right now though, I just want speed. I then found the std::bitset object from

Java BitSet Example

由 生来就可爱ヽ(ⅴ＜●) 提交于 2019-11-26 08:49:13
问题 I\'m looking for a good Java BitSet example to work with 0 and 1s. I tried looking at the Javadocs but I don\'t understand the usage of the class by just reading that. For instance, how would the and , or , and xor methods work on two different BitSet objects? For example: BitSet bits1 = new BitSet(); BitSet bits2 = new BitSet(); bits2.set(1000001); bits1.set(1111111); bits2.and(bits1); System.out.println(bits2); If I do this it returns bits2 as empty why is that? 回答1: For the specific
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