bit-manipulation

Consider a bit vector of N bits in it ( N is large) and an array of M numbers ( M is moderate, usually much smaller than N ), each in range 0..N-1 indicating which bit of the vector must be set to 1 . The latter array is not sorted. The bit vector is just an array of integers, specifically __m256i , where 256 bits are packed into each __m256i structure. How can this work be split efficiently accross multiple threads? Preferred language is C++ (MSVC++2017 toolset v141), assembly is also great. Preferred CPU is x86_64 (intrinsics are ok). AVX2 is desired, if any benefit from it. Let's assume you

In Golang, how do you set and clear individual bits of an integer? For example, functions that behave like this: clearBit(129, 7) // returns 1 setBit(1, 7) // returns 129 Here's a function to set a bit. First, shift the number 1 the specified number of spaces in the integer (so it becomes 0010, 0100, etc). Then OR it with the original input. This leaves the other bits unaffected but will always set the target bit to 1. // Sets the bit at pos in the integer n. func setBit(n int, pos uint) int { n |= (1 << pos) return n } Here's a function to clear a bit. First shift the number 1 the specified

Though GPUs are supposed for use with floating point data types, I'd be interested in how fast can GPU process bitwise operations. These are the fastest possible on CPU, but does GPU emulate bitwise operations or are they fully computed on hardware? I'm planning to use them inside shader programs written with GLSL. Also I'd suppose that if bitwise operations have full preformance, integer data types should have also, but I need confirmation on that. To be more precise, targeted versions are OpenGL 3.2 and GLSL 1.5. Hardware that should run this is any Radeon HD graphics card and GeForce series

Here's a tough one(atleast i had a hard time :P): find the index of the highest bit set of a 32-bit number without using any loops. With recursion: int firstset(int bits) { return (bits & 0x80000000) ? 31 : firstset((bits << 1) | 1) - 1; } Assumes [31,..,0] indexing Returns -1 if no bits set | 1 prevents stack overflow by capping the number of shifts until a 1 is reached (32) Not tail recursive :) Floor of logarithm-base-two should do the trick (though you have to special-case 0). Floor of log base 2 of 0001 is 0 (bit with index 0 is set). " " of 0010 is 1 (bit with index 1 is set). " " of

How to swap the nybble bit positions of a number? For example: 534, convert it into binary, the rightmost 4 bits has to be interchanged with the leftmost 4 bits and then make a new number with that. Anyone know how to do this? Start from the fact that hexadecimal 0xf covers exactly four bits. There are four nibbles in a 16-bit number. The masks for the nibbles are 0xf000 , 0xf00 , 0xf0 , and 0xf . Then start masking, shifting and bitwise OR-ing. Sean Anderson's bit twiddling guide has the following: // swap nibbles ... v = ((v >> 4) & 0x0F0F0F0F) | ((v & 0x0F0F0F0F) << 4); under the entry for