bitarray

How can I unset the most significant setted bit of a word (e.g. 0x00556844 -> 0x00156844)? There is a __builtin_clz in gcc, but it just counts the zeroes, which is unneeded to me. Also, how should I replace __builtin_clz for msvc or intel c compiler? Current my code is int msb = 1<< ((sizeof(int)*8)-__builtin_clz(input)-1); int result = input & ~msb; UPDATE: Ok, if you says that this code is rather fast, I'll ask you, how should I add a portability to this code? This version is for GCC, but MSVC & ICC? Just round down to the nearest power of 2 and then XOR that with the original value, e.g.

I'm designing a bloom filter and I'm wondering what the most performant bit array implementation is in Python. The nice thing about Python is that it can handle arbitrary length integers out of the box and that's what I use now, but I don't know enough about Python internals to know if that's the most performant way to do it in Python. I found bitarray but it handles a lot of other things like slicing, which I don't need. I only need the & and | and << operations. The built-in int is pretty nicely optimized, and it already supports & , | , and << . There's at least one alternative

I am working on a Python library that performs a lot of bitwise operations on long bit strings, and I want to find a bit string type that will maximize its speed. I have tried the built-in Python int type, numpy, bitstring , and bitarray , and suprisingly, the Python ints seem to win hands down when it comes to bitwise operations. Everything I have googled says numpy should be much faster for vectorized operations like this. Am I using numpy wrong somehow? Is there another Python library I can use that actually improves on Python's built-in int type? from timeit import timeit import random

Is there some reasonably fast code out there which can help me quickly search a large bitmap (a few megabytes) for runs of contiguous zero or one bits? By "reasonably fast" I mean something that can take advantage of the machine word size and compare entire words at once, instead of doing bit-by-bit analysis which is horrifically slow (such as one does with vector<bool> ). It's very useful for e.g. searching the bitmap of a volume for free space (for defragmentation, etc.). Windows has an RTL_BITMAP data structure one can use along with its APIs. But I needed the code for this sometime ago,

Is there any predefined function available to convert a byte into BitArray ? One way would be to inspect every bit of the byte value and then perform bitwise operation. I was wondering if there is any way which is more straightforward than this. CodeCaster Yes, using the appropriate BitArray() constructor as described here : var bits = new BitArray(arrayOfBytes); You can call it with new BitArray(new byte[] { yourBite }) to create an array of one byte. if you have a byte number or even an integer, etc. BitArray myBA = new BitArray(BitConverter.GetBytes(myNumber).ToArray()); Note: you need a

I am implementing a library where I am extensively using the .Net BitArray class and need an equivalent to the Java BitSet.Cardinality() method, i.e. a method which returns the number of bits set. I was thinking of implementing it as an extension method for the BitArray class. The trivial implementation is to iterate and count the bits set (like below), but I wanted a faster implementation as I would be performing thousands of set operations and counting the answer. Is there a faster way than the example below? count = 0; for (int i = 0; i < mybitarray.Length; i++) { if (mybitarray [i]) count+