bitcount

Say you have two binary values 001011 001111 How can you get the number of different bits in MySQL? I tried SELECT BIT_COUNT(BINARY 001011 ^ BINARY 001111) This returns 6, while I need a solution that returns 1 in this example. SELECT BIT_COUNT( CONV( '001011', 2, 10 ) ^ CONV( '001111', 2, 10 ) ) SELECT BIT_COUNT(b'001011' ^ b'001111'); It's converting the numbers 1011 and 1111 (base 10) to binary and doing the comparison. If you did: SELECT BIT_COUNT(11 ^ 15) It'd work. 来源： https://stackoverflow.com/questions/7111728/comparing-binary-values-in-mysql

I want to count the bits that are set in an extremely large bit-vector (i.e. 100,000 bits). What I am currently doing is using a pointer to char (i.e. char *cPtr) to point to the beginning of the array of bits. I then: 1. look at each element of the array (i.e. cPtr[x]), 2. convert it to an integer (i.e. (int) cPtr[x]) 3. use a 256 element look-up table to see how many bits are set in the given byte (i.e. cPtr[x]). It occurs to me that if I use a short int pointer instead (i.e. short int * sPtr), then I will only need half as many look-ups, but with a 65534 element look-up table, which will

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 to represent a positive integer in Python? SilentGhost In python 2.7+ there is a int.bit_length() method: >>> a = 100 >>> a.bit_length() 7 >>> len(bin(1000))-2 10 >>> len(bin(100))-2 7 >>> len(bin(10))-2 4 Note : will not work for negative numbers, may be need to substract 3 instead of 2 Gilles If your Python version has it (≥2.7 for Python 2, ≥3.1 for Python 3), use the bit_length method from the standard library.

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 AVX-512 has a VPOPCNTDQ instruction which counts the number of 1 bits in each consecutive 64 bits within a 512-bit vector, and IIANM it should be possible to issue one of these every cycle (if an appropriate SIMD vector register is available) - but I don't have any experience writing SIMD code (I'm more of a GPU guy). Also, I'm not 100% sure about compiler support for AVX-512 targets. On most CPUs,