bitmask

问题 I can think of three ways to do this off the top of my head. I'll outline them real quick. char mask = (1<<top) mask = mask-1 mask = mask>>bot mask = mask<<bot 3 shifts, 1 addition char topMask = (1<<top) topMask = topMask -1 char botMask = (1<<bot) botMask = botMask - 1 char mask = topMask - botMask 2 shifts, 3 additions char mask = (1<<(top-bot)) mask = mask - 1 mask = mask << bot 2 shifts, 2 additions It seems like the first one would be a little faster? Is one considered best for style

问题 Coming across this situation both in Sprite Kit (iOS Development) and in Cocos2d-x (which I know was pretty much the inspiration for Sprite Kit, hence why they use a lot of the same tools), I finally decided to figure out why this happens: When using a physic engine, I create a sprite, and add a physicsBody to it. For the most part, I understand how to set the category, collision, and contact bitmasks, and how they work. The problem is the actual bitmask number: SpriteKit: static const uint32

问题 On the PHP documentation about JSON it mentions the word bitmask. Wikipedia has it defined as a mask. I don't understand either bitmask or mask or how they are useful. Can some one explain these terms using layman's terms and no jargon? 回答1: Bits and Bytes In computing, numbers are internally represented in binary. This means, where you use an integer type for a variable, this will actually internally will be represented as a summation of zeros and ones. As you might know, a single bit

问题 Bits and bitmask are something I have been struggling to understand for a while, but I would like to learn how to use them for settings and things like that in PHP. I have finally found a class that claims to do exactly that, and as I can tell, it seems to work, but I am not sure if it is the best way of doing this. I will post the class file with example code below to show it in working order. Please if you have experience, tell me if it can be improved, for performance or anything else. I

问题 Is there any efficient code to generate numbers with n digits in their binary representation with exactly r bits set as one? Also is this a good strategy to generate masks for finding NcR combinations of a set? I've thought about generating all 2^n numbers and counting their bits but counting bits seems to be O(nlogn). 回答1: Well, if we are given a number with K bits set, how can we find the next largest number with K bits set? If we do this repeatedly we can generate all of them. Generating

问题 I am working on an application that have some categories. The aim is to store the categories in a value. First, I choosed to store them in an int. Categories : 0, 1, 2, 3... Then I do a bitmask operation to find which category was selected. But the problem is that I can't store more that 31 categories is this int. Is there any way to make such system ? I don't want to go threw the unlimited number of categories but maybe over 64. The target language is C# but any other solution could be fine.

问题 We have an interesting challenge. We have to control access to data that reside in "bins". There will be, potentially, hundreds of thousands of "bins". Access to each bin is controlled individually but the restrictions can, and probably will, overlap. We are thinking of assigning each bin a position in a bitmask (1,2,3,4, etc..). Then when a user logs into the system, we look at his security attributes and determine which bins he's allowed to see. With that info we construct a bitmask for

问题 This most likely has been asked and answered before, but my searches was futile. Question is about bits, bytes masks and checking. Say one have two "triggers" 0xC4 and 0xC5 : 196: 1100 0100 0xc4 197: 1100 0101 0xc5 The simple way of checking if var is either would be: if (var == 0xc5 || var == 0xc4) { } But sometimes one see this (or the like): if ( ((var ^ magic) & mask) == 0) { } My question is how to find magic and mask . What methods, procedures, tricks etc. is to be utilized to form

问题 Currently I have a solution where I keep track of objects I am interested in by getting their hashcode via Object.GetHashCode and then storing them in a HashSet<int> . However, I have also been learning about bitmasks and bitwise operations and I am quite intrigued by them. Here is a great question that I found close to what I am looking to do. However, I cannot seem to make this work efficiently for hash codes. There is also this question, but it seems to deal with 5-bit numbers, when hash

问题 My current hobby project provides Monte-Carlo-Simulations for card games with French decks (52 cards, from 2 to Ace). To simulate as fast as possible, I use to represent multiple cards as bitmasks in some spots. Here is some (simplified) code: public struct Card { public enum CardColor : byte { Diamonds = 0, Hearts = 1, Spades = 2, Clubs = 3 } public enum CardValue : byte { Two = 0, Three = 1, Four = 2, Five = 3, Six = 4, Seven = 5, Eight = 6, Nine = 7, Ten = 8, Jack = 9, Queen = 10, King =