I have a square boolean matrix M of size N, stored by rows and I want to count the number of bits set to 1 for each column. For instance for n=4: 1101 0101 0001 1001 M stored as { { 1,1,0,1}, {0...

I was trying to how many 1 in 512MB memory and I found two possible methods, _mm_popcnt_u64() and __builtin_popcountll() in the gcc builtins. _mm_popcnt_u64() is said to use the CPU introduction S...

While watching this talk by Matt Godbolt, I was astonished to see that Clang, if instructed to compile for the Haswell¹ architecture, works out that the following code int foo(int a) { int count =...

I have found out about __builtin_ctzll to count trailing zeros of a 64bit int really fast through the post Intrinsic to count trailing zero bits in 64-bit integers?. I'm a beginner to C++ and don't...

I am interested, which is the optimal way of calculating the number of bits set in byte by this way template< unsigned char byte > class BITS_SET { public: enum { B0 = (byte & 0x01) ? ...

I need a fast way to count the number of bits in an integer in python. My current solution is bin(n).count("1") but I am wondering if there is any faster way of doing this?

What is the Big O of bit count? I'm not sure how the method works, but I would assume it is done in O(logn). Specifically with this code (where x = 4, y = 1): return Integer.bitCount(x^y);

I have got a binary number of length 8 for eg 00110101 There are 8 bits set. I need a fast bit count to determine the number of set bits, the popcount aka population count. Running the algo like th...

1 = 0b1 -> 1 5 = 0b101 -> 3 10 = 0b1010 -> 4 100 = 0b1100100 -> 7 1000 = 0b1111101000 -> 10 … How can I get the bit length of an integer, i.e. the number of bits that are necessary...

I have a long chunk of memory, say, 256 KiB or longer. I want to count the number of 1 bits in this entire chunk, or in other words: Add up the "population count" values for all bytes. I know that...

I need some explanation how this specific line works. I know that this function counts the number of 1's bits, but how exactly this line clears the rightmost 1 bit? int f(int n) { int c; ...

MySQL's bit_count function is quite useful for some cases: http://dev.mysql.com/doc/refman/5.5/en/bit-functions.html#function_bit-count Now I would like to use that function in other databases, t...

I've seen the numerous questions about counting the number of set bits in an insert type of input, but why is it useful? For those looking for algorithms about bit counting, look here: Counting ...

I'm using Java and I'm coding a chess engine. I'm trying to find the index of the first 1 bit and the index of the last 1 bit in a byte. I'm currently using Long.numberOfTrailingZeros() (or somet...

What is the best solution for getting the base 2 logarithm of a number that I know is a power of two (2^k). (Of course I know only the value 2^k not k itself.) One way I thought of doing is by sub...