Count number of bits in a 64-bit (long, big) integer?
I have read through this SO question about 32-bits, but what about 64-bit numbers? Should I just mask the upper and lower 4 bytes, perform the count on the 32-bits and then add them together? ...
bit-manipulation
Adding to a bit array
In my program, I am using BitArrays to represent 160 bit numbers. I want to be able to add, subtract, increment and decrement these numbers, what is the algorithm for doing this? At the moment I'm not interested in multiplication and division, but I might be in the future so bonus points for that. I'm implementing in C#, but pseudocode...
Efficient bitshifting an array of int?
Hi, To be on the same page, let's assume sizeof(int)=4 and sizeof(long)=8. Given an array of integers, what would be an efficient method to logically bitshift the array to either the left or right? I am contemplating an auxiliary variable such as a long, that will compute the bitshift for the first pair of elements (index 0 and 1) and...
binary number comparison
If I have a 32 bit two's complement number and I want to know what is the easiest way to know of two numbers are equal... what would be the fastest bitwise operator to know this? I know xor'ing both numbers and check if the results are zero works well... any other one's? how about if a number is greater than 0?? I can check the 31'st bi...
Convert 0 to 1 and Vice Versa
I was asked in an interview : how to convert 0 to 1 and 1 to 0. I answered : Simple if and switch Bit flipping. Are there any other approach? ...
What does >> mean in PHP?
echo 50 >> 4; Output: 3 Does anyone know why it outputs 3? ...
Finding N contiguous zero bits in an integer to the left of the MSB position of another integer
The problem is: given an integer val1 find the position of the highest bit set (Most Significant Bit) then, given a second integer val2 find a contiguous region of unset bits to the left of the position yielded from the first integer. width specifies the minimum number of unset bits that must be found in contiguity (ie width zeros withou...
Convert bit vector (array of booleans) to an integer, and integer to bit vector, in Java.
What's the best way to unstub the following functions? // Convert a bit-vector to an integer. int bitvec2int(boolean[] b) { [CODE HERE] } // Convert an integer x to an n-element bit-vector. boolean[] int2bitvec(int x, int n) { [CODE HERE] } Or is there a better way to do that sort of thing than passing boolean arrays around...
Looking for advice on how to do some bit-twiddling
Suppose I have the array int a[] = new int[] { 0xBCDA, 0xABFE, 0xBCAD, 0xEFCA, 0xFFCA } I know that there is always some hexadecimal number which occurs in all number or in this case A is repeated in the array everywhere so my aim is print only the repeated number and other numbers should be zero, so my new array should be like thi...
Do bit operations cause programs to run slower?
I'm dealing with a problem which needs to work with a lot of data. Currently its values are represented as an unsigned int. I know that real values do not exceed a limit of 1000. Questions I can use unsigned short to store it. An upside to this is that it'll use less storage space to store the value. Will performance suffer? If I dec...
Python proper use of __str__ and __repr__
Hey, My current project requires extensive use of bit fields. I found a simple, functional recipe for bit a field class but it was lacking a few features I needed, so I decided to extend it. I've just got to implementing __str__ and __repr__ and I want to make sure I'm following convention. __str__ is supposed to be informal and conci...
java.util.BitSet -- set() doesn't work as expected
Am I missing something painfully obvious? Or does just nobody in the world actually use java.util.BitSet? The following test fails: @Test public void testBitSet() throws Exception { BitSet b = new BitSet(); b.set(0, true); b.set(1, false); assertEquals(2, b.length()); } It's really unclear to me why I don't end up wi...
Bit manipulation, permutate bits
Hi. I am trying to make a loop that loops through all different integers where exactly 10 of the last 40 bits are set high, the rest set low. The reason is that I have a map with 40 different values, and I want to sum all different ways ten of these values can be multiplied. (This is just out of curiosity, so it's really the "bitmanip"-...
Getting the Leftmost Bit
I have a 5 bit integer that I'm working with. Is there a native function in Objective-C that will let me know which bit is the leftmost? i.e. I have 01001, it would return 8 or the position. Thanks ...
Speed up bitstring/bit operations in Python?
I wrote a prime number generator using Sieve of Eratosthenes and Python 3.1. The code runs correctly and gracefully at 0.32 seconds on ideone.com to generate prime numbers up to 1,000,000. # from bitstring import BitString def prime_numbers(limit=1000000): '''Prime number generator. Yields the series 2, 3, 5, 7, 11, 13, 17, 19,...
Fastest method to define whether a number is a triangular number
A triangular number is the sum of the n natural numbers from 1 to n. What is the fastest method to find whether a given positive integer number is a triangular one? ...
NASM: Count how many bits in a 32 Bit number are set to 1.
I have a 32 Bit number and want to count know how many bits are 1. I'm thinking of this pseudocode: mov eax, [number] while(eax != 0) { div eax, 2 if(edx == 1) { ecx++; } shr eax, 1 } Is there a more efficient way? I'm using NASM on a x86 processor. (I'm just beginning with assembler, so please do not tell me to use ...
Bit Flipping in Hex
I have an 8 digit hexadecimal number of which I need certain digits to be either 0 or f. Given the specific place of the digits is there a quick way to generate the hex number with those places "flipped" to f. For example: flip_digits(1) = 0x000000f flip_digits(1,2,4) = 0x0000f0ff flip_digits(1,7,8) = 0xff00000f I'm doing this on an...
Bit conversion operations in PHP
Hello, I find myself in need of performing bit-level conversion on variables in PHP. In more detail, I have a bit stream that is read as an integer by hardware, and I need to do some operations on the bits to make it into what its actually supposed to be (a float). I have to do this a few times for different formats, and the functionali...
C Population Count of unsigned 64-bit integer with a maximum value of 15
I use a population count (hamming weight) function intensively in a windows c application and have to optimize it as much as possible in order to boost performance. More than half the cases where I use the function I only need to know the value to a maximum of 15. The software will run on a wide range of processors, both old and new. I a...