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• How does the bitwise operator '^' work?

  - by SpawnCxy

  I'm a little confused when I see the output of following code: $x = "a"; $y = "b"; $x ^= $y; $y ^= $x; $x ^= $y; echo $x; //got b echo $y; //got a And I wonder how does the operator ^ work here?Explanations with clarity would be greatly appreciated!

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• Bitwise operations in BC?

  - by user355926

  $ bc BC> ibase=2 BC> 110&101 // wanna get 100 (standar_in) 8: syntax error Wikipedia informs that the ops are "|, & and ^". It may be that they work only in certain BC-types or I misread something.

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• How to reverse bitwise AND (&) in C ?

  - by VaioIsBorn

  For example i have an operation in C like this: ((unsigned int)ptr & 0xff000000)) The result is bf000000. What do i need at this moment is how to reverse the above i.e. determine the ptr by using the result from the operation and offcourse 0xff000000 . I am asking if there's any simple way to implement this in C, tnx.

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• YouTube: Tips by Bitwise Courses on NetBeans

  - by Geertjan

  I really like the potential of YouTube in providing a platform for short info clips that take not much time to produce and about as much time to consume. Huw Collingbourne's Bitwise Courses channel is full of exactly this kind of YouTube clip. Several of his YouTube clips are about or make use of NetBeans. The related Twitter account is @bitwisecourses and the homepage is bitwisecourses.com. Here's a great example, the latest YouTube clip created by Bitwise Courses. Very clear and simple explanation, on a specific and narrow topic, and very short and sweet. And very useful! Didn't know about this feature myself. Direct link to the movie: https://www.youtube.com/watch?v=b0fKT_hFQpU Here's to more of these, they're wonderful. More such YouTube clips are needed, short and precise, on very specific topics. And I'm very happy to promote them, as you can see.

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• How to define 2-bit numbers in C, if possible?

  - by Eddy

  For my university process I'm simulating a process called random sequential adsorption. One of the things I have to do involves randomly depositing squares (which cannot overlap) onto a lattice until there is no more room left, repeating the process several times in order to find the average 'jamming' coverage %. Basically I'm performing operations on a large array of integers, of which 3 possible values exist: 0, 1 and 2. The sites marked with '0' are empty, the sites marked with '1' are full. Initially the array is defined like this: int i, j; int n = 1000000000; int array[n][n]; for(j = 0; j < n; j++) { for(i = 0; i < n; i++) { array[i][j] = 0; } } Say I want to deposit 5*5 squares randomly on the array (that cannot overlap), so that the squares are represented by '1's. This would be done by choosing the x and y coordinates randomly and then creating a 5*5 square of '1's with the topleft point of the square starting at that point. I would then mark sites near the square as '2's. These represent the sites that are unavailable since depositing a square at those sites would cause it to overlap an existing square. This process would continue until there is no more room left to deposit squares on the array (basically, no more '0's left on the array) Anyway, to the point. I would like to make this process as efficient as possible, by using bitwise operations. This would be easy if I didn't have to mark sites near the squares. I was wondering whether creating a 2-bit number would be possible, so that I can account for the sites marked with '2'. Sorry if this sounds really complicated, I just wanted to explain why I want to do this.

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• One position right barrel shift using ALU Operators?

  - by Tomek

  I was wondering if there was an efficient way to perform a shift right on an 8 bit binary value using only ALU Operators (NOT, OR, AND, XOR, ADD, SUB) Example: input: 00110101 output: 10011010 I have been able to implement a shift left by just adding the 8 bit binary value with itself since a shift left is equivalent to multiplying by 2. However, I can't think of a way to do this for shift right. The only method I have come up with so far is to just perform 7 left barrel shifts. Is this the only way?

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• Java print binary number using bit-wise operator

  - by user69514

  Hi I am creating a method that will take a number and print it along with its binary representation. The problems is that my method prints all 0's for any positive number, and all 1's for any negative number private static void display( int number ){ System.out.print(number + "\t"); int mask = 1 << 31; for(int i=1; i<=32; i++) { if( (mask & number) != 0 ) System.out.print(1); else System.out.print(0); if( (i % 4) == 0 ) System.out.print(" "); } }

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• Bitwise operators in DX9 ps_2_0 shader

  - by lapin

  I've got the following code in a shader: // v & y are both floats nPixel = v; nPixel << 8; nPixel |= y; and this gives me the following error in compilation: shader.fx(80,10): error X3535: Bitwise operations not supported on legacy targets. shader.fx(92,18): ID3DXEffectCompiler::CompileEffect: There was an error compiling expression ID3DXEffectCompiler: Compilation failed The error is on the following line: nPixel |= y; What am I doing wrong here?

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• Ouya / Android : button mapping bitwise

  - by scorvi

  I am programming a game with the Gameplay3d Engine. But the Android site has no gamepad support and that is what I need to port my game to Ouya. So I implemented a simple gamepad support and it supports 2 gamepads. So my problem is that I put the button stats in a float array for every gamepad. But the Gameplay3d engine saves their stats in a unsigned int _buttons variable. It is set with bitwise operations and I have no clue how to translate my array to this.

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• What are these values representative of in C bitwise operations?

  - by ajax81

  Hi All, I'm trying to reverse the order of bits in C (homework question, subject: bitwise operators). I found this solution, but I'm a little confused by the hex values (?) used -- 0x01 and 0x80. unsigned char reverse(unsigned char c) { int shift; unsigned char result = 0; for (shift = 0; shift < CHAR_BITS; shift++) { if (c & (0x01 << shift)) result |= (0x80 >> shift); } return result; } The book I'm working out of hasn't discussed these kinds of values, so I'm not really sure what to make of them. Can somebody shed some light on this solution? Thank you!

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• Any significant performance improvement by using bitwise operators instead of plain int sums in C#?

  - by tunnuz

  Hello, I started working with C# a few weeks ago and I'm now in a situation where I need to build up a "bit set" flag to handle different cases in an algorithm. I have thus two options: enum RelativePositioning { LEFT = 0, RIGHT = 1, BOTTOM = 2, TOP = 3, FRONT = 4, BACK = 5 } pos = ((eye.X < minCorner.X ? 1 : 0) << RelativePositioning.LEFT) + ((eye.X > maxCorner.X ? 1 : 0) << RelativePositioning.RIGHT) + ((eye.Y < minCorner.Y ? 1 : 0) << RelativePositioning.BOTTOM) + ((eye.Y > maxCorner.Y ? 1 : 0) << RelativePositioning.TOP) + ((eye.Z < minCorner.Z ? 1 : 0) << RelativePositioning.FRONT) + ((eye.Z > maxCorner.Z ? 1 : 0) << RelativePositioning.BACK); Or: enum RelativePositioning { LEFT = 1, RIGHT = 2, BOTTOM = 4, TOP = 8, FRONT = 16, BACK = 32 } if (eye.X < minCorner.X) { pos += RelativePositioning.LEFT; } if (eye.X > maxCorner.X) { pos += RelativePositioning.RIGHT; } if (eye.Y < minCorner.Y) { pos += RelativePositioning.BOTTOM; } if (eye.Y > maxCorner.Y) { pos += RelativePositioning.TOP; } if (eye.Z > maxCorner.Z) { pos += RelativePositioning.FRONT; } if (eye.Z < minCorner.Z) { pos += RelativePositioning.BACK; } I could have used something as ((eye.X > maxCorner.X) << 1) but C# does not allow implicit casting from bool to int and the ternary operator was similar enough. My question now is: is there any performance improvement in using the first version over the second? Thank you Tommaso

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• how to calculate bitwise OR using AND, XOR and shift?

  - by Flavius

  Hi The question seems pretty well formulated I have a virtual machine which implements only AND, XOR, SHL and SHR, yet I have to do a "OR 0x01" operation.

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• bitwise AND in Javascript with a 64 bit integer

  - by Toby Hede

  I am looking for a way of performing a bitwise AND on a 64 bit integer in JavaScript. JavaScript will cast all of its double values into signed 32-bit integers to do the bitwise operations (details here).

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• I (think) I want to use a BItWise Operator to check useraccountcontrol property!

  - by Jim

  Hello, Here's some code: DirectorySearcher searcher = new DirectorySearcher(); searcher.Filter = "(&(objectClass=user)(sAMAccountName=" + lstUsers.SelectedItem.Text + "))"; SearchResult result = searcher.FindOne(); Within result.Properties["useraccountcontrol"] will be an item which will give me a value depending on the state of the account. For instance, a value of 66050 means I'm dealing with: A normal account; where the password does not expire;which has been disabled. Explanation here. What's the most concise way of finding out if my value "contains" the AccountDisable flag (which is 2) Thanks in advance!

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• PHP equilavent javascript >>> shift right with zero fill bitwise operators?

  - by neobie

  May I know how can I do PHP ? Such operators is not available in PHP, but is available in Javascript. I just managed to discover a function as follow: function zeroFill($a, $b) { $z = hexdec(80000000); if ($z & $a) { $a = ($a>>1); $a &= (~$z); $a |= 0x40000000; $a = ($a>>($b-1)); } else { $a = ($a>>$b); } return $a; } but unfortunately, it doesn't work perfectly.

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• Is there something special about the number 65535?

  - by Nick Rosencrantz

  2¹6-1 & 25 = 25 (or? obviously ?) A developer asked me today what is bitwise 65535 & 32 i.e. 2¹6-1 & 25 = ? I thought at first spontaneously 32 but it seemed to easy whereupon I thought for several minutes and then answered 32. 32 seems to have been the correct answer but how? 65535=2¹6-1=1111111111111111 (but it doesn't seem right since this binary number all ones should be -1(?)), 32 = 100000 but I could not convert that in my head whereupon I anyway answered 32 since I had to answer something. Is the answer 32 in fact trivial? Is in the same way 2¹6-1 & 25-1 =31? Why did the developer ask me about exactly 65535? Binary what I was asked to evaluate was 1111111111111111 & 100000 but I don't understand why 1111111111111111 is not -1. Shouldn't it be -1? Is 65535 a number that gives overflow and how do I know that?

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• Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

  - by Leron

  I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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• What is the point of the logical operators in C?

  - by reubensammut

  I was just wondering if there is an XOR logical operator in C (something like && for AND but for XOR). I know I can split an XOR into ANDs, NOTs and ORs but a simple XOR would be much better. Then it occurred to me that if I use the normal XOR bitwise operator between two conditions, it might just work. And for my tests it did. Consider: int i = 3; int j = 7; int k = 8; Just for the sake of this rather stupid example, if I need k to be either greater than i or greater than j but not both, XOR would be quite handy. if ((k > i) XOR (k > j)) printf("Valid"); else printf("Invalid"); or printf("%s",((k > i) XOR (k > j)) ? "Valid" : "Invalid"); I put the bitwise XOR ^ and it produced "Invalid". Putting the results of the two comparisons in two integers resulted in the 2 integers to contain a 1, hence the XOR produced a false. I've then tried it with the & and | bitwise operators and both gave the expected results. All this makes sense knowing that true conditions have a non zero value, whilst false conditions have zero values. I was wondering, is there a reason to use the logical && and || when the bitwise operators &, | and ^ work just the same? Thanks Reuben

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• bitwise not operator .

  - by Tony

  Why bitwise operation (~0); prints -1 ? In binary , not 0 should be 1 . why ?

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• How to make ARGB transparency using bitwise operators.

  - by Smejda

  I need to make transparency, having 2 pixels: pixel1: {A, R, G, B} - foreground pixel pixel2: {A, R, G, B} - background pixel A,R,G,B are Byte values each color is represented by byte value now I'm calculating transparency as: newR = pixel2_R * alpha / 255 + pixel1_R * (255 - alpha) / 255 newG = pixel2_G * alpha / 255 + pixel1_G * (255 - alpha) / 255 newB = pixel2_B * alpha / 255 + pixel1_B * (255 - alpha) / 255 but it is too slow I need to do it with bitwise operators (AND,OR,XOR, NEGATION, BIT MOVE)

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• Bitwise Operations on Rows of lil_matrix

  - by Ryan Rosario

  How can I quickly extract two rows of a scipy.sparse.lil_matrix and apply bitwise operations on them? I've tried: np.bitwise_and(A[1,:], A[2,:]) but NumPy seems to want an array type according to the documentation.

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• Concept of bit fields

  - by user1369975

  Whenever I read a code like this: struct node { int x : 2; int p : 4; }n; with bit fields involved, I get really confused, as to how they are represented in memory, what is sizeof(n) etc., how does it differ with normal members of structures? I tried referring K&R and http://en.wikipedia.org/wiki/Bit_field but they little to remove my confusion. What concepts of bit fields am I failing to grasp?

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• Arithmetic + and Bitwise OR

  - by Mohanavel

  Is there any difference between Arithmetic + and bitwise OR. For the below operation i used arithmetic operation, my friend told that this is wrong. In what way this is differing. uint a = 10; uint b = 20; uint arithmeticresult = a + b; uint bitwiseOR = a | b; Both the results are 30.

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• Strlen of MAX 16 chars string using bitwise operators

  - by fabrizioM

  The challenge is to find the fastest way to determine in C/C++ the length of a c-string using bitwise operations in C. char thestring[16]; The c-string has a max size of 16 chars and is inside a buffer If the string is equal to 16 chars doesn't have the null byte at the end. I am sure can be done but didn't got it right yet. I am working on this at the moment, but assuming the string is memcpied on a zero-filled buffer. len = buff[0] != 0x0 + buff[1] != 0x0 + buff[2] != 0x0 + buff[3] != 0x0 + buff[4] != 0x0 + buff[5] != 0x0 + buff[6] != 0x0 + buff[7] != 0x0 + buff[8] != 0x0 + buff[9] != 0x0 + buff[10] != 0x0 + buff[11] != 0x0 + buff[12] != 0x0 + buff[13] != 0x0 + buff[14] != 0x0 + buff[15] != 0x0;

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• Simple Python Challenge: Fastest Bitwise XOR on Data Buffers

  - by user213060

  Challenge: Perform a bitwise XOR on two equal sized buffers. The buffers will be required to be the python str type since this is traditionally the type for data buffers in python. Return the resultant value as a str. Do this as fast as possible. The inputs are two 1 megabyte (2**20 byte) strings. The challenge is to substantially beat my inefficient algorithm using python or existing third party python modules (relaxed rules: or create your own module.) Marginal increases are useless. from os import urandom from numpy import frombuffer,bitwise_xor,byte def slow_xor(aa,bb): a=frombuffer(aa,dtype=byte) b=frombuffer(bb,dtype=byte) c=bitwise_xor(a,b) r=c.tostring() return r aa=urandom(2**20) bb=urandom(2**20) def test_it(): for x in xrange(1000): slow_xor(aa,bb)

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