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Questions tagged [bitcount]

42 questions
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Bit counting arbitrarily large positive integers in C#

There are many implementations of bit counting out there but in my case, I need to test if an arbitrarily large number contains at most two set bits. I wrote the following function that does the job and seems to be quite fast but I wanted to find…
Raheel Khan
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Matrix transpose and population count

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}, {0,1,0,1}, {0,0,0,1}, {1,0,0,1} }; result = { 2, 2, 0,…
edrezen
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Counting number of '1' values in each bit position in Redshift column

I have BIGINT column in my Redshift table, and I want a query that will: Count how many times the value '1' appears in each bit position across the binary value in all the rows of this column Will show it in a way that I'll be able to take the x…
JustinCase
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Trailing/leading zero count for a byte

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 something like that) in Java, and would like to emulate…
solinent
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MongoDB support search Bitwise XOR and Bit Count?

I would like to move from MYSQL to MongoDB, one of the question I can not find answer for, if I can get or simulate XOR and Bit Count, which I need. In MYSQL I would do: SELECT BIT_COUNT(SimHash ^ $SimHash) as simhash ... ORDER BY simhash It is…
2ge
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Why does Integer.bitCount() return 8 for an input of 255?

The Java API for Integer.bitCount() tells us: "public static int bitCount(int i) Returns the number of one-bits in the two's complement binary representation of the specified int value. This function is sometimes referred to as the population…
Jonathan Sterling
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How can I know the bit count of a cpu/os in C

I know how to get the bit count of a cpu or an operation system with shell. cat /proc/cpuinfo | grep lm #-> get bit count of a cpu uname -a #-> get bit count of an operation system However, how can we get the bit count of those…
xianyu1337
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Bit Twiddling in C - Counting Bits

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…
user1245262
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How to simulate the MySQL bit_count function in Sybase SQL Anywhere?

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, that do not support it. What's the simplest way to do…
Lukas Eder
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XOR operation and BitCount in Java on Long variables returns java.lang.NumberFormatException

I am trying to do a XOR operation on two 64 bits Long variables in Java. The problem is that it fails when I add more than 16 bits in a variable. For instance this works and returns 7: Long h1 = Long.parseLong("1100001101001101"); Long h2 =…
c1377554
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PHP equivalent of C code from Bit Twiddling Hacks?

http://www-graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel v = v - ((v >> 1) & (T)~(T)0/3); // temp v = (v & (T)~(T)0/15*3) + ((v >> 2) & (T)~(T)0/15*3); // temp v = (v + (v >> 4)) & (T)~(T)0/255*15; …
user323094
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Can someone explain how this bitCount code works?

This is code that my TA help me get, but then I completely forgot how it worked exactly since I can't seem to get the right answer, and the interview grading is tomorrow. If anybody can help please do. Thanks * bitCount - returns count of number of…
Ryan Fasching
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Counting number of 1 bits in C++ negative number

The following function: int numOnesInBinary(int number) { int numOnes = 0; while (number != 0) { if ((number & 1) == 1) { numOnes++; } number >>= 1; } return numOnes; } will only work for positive…
programmer
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LC3 Bit Counter

I'm trying to figure out how to implement a bit counter in LC3 assembly language. ex: input "00001100001000001" output "000000000000100" I would be counting the number of ones in the string of bits and outputting that number in binary. I know how…
CDO
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Is there a big.BitCount?

Is there an already-written BitCount method for big.Int? There doesn't seem to be one in math/big. Obviously I will write one myself if not - does anyone have one already written? I want the number of set bits in the number. Like Java…
OldCurmudgeon
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