bit-manipulation

问题 Say I was to write this: a=01100001 b=01100010 c=01100011 d=01100100 e=01100101 each letter resembles the given numbers now how would I deal with the resembling values: Python would want to do this: a + b = 2200011 but what I want it to do is this if 0 and 0 are attempted to be added together show 1 if 1 and 0 are attempted to be added together show 0 if 0 and 1 are attempted to be added together show 0 if 1 and 1 are attempted to be added together show 0 What I wish to do is a + b = 10011100

问题 Given a MATLAB uint32 to be interpreted as a bit string, what is an efficient and concise way of counting how many nonzero bits are in the string? I have a working, naive approach which loops over the bits, but that's too slow for my needs. (A C++ implementation using std::bitset count() runs almost instantly). I've found a pretty nice page listing various bit counting techniques, but I'm hoping there is an easy MATLAB-esque way. http://graphics.stanford.edu/~seander/bithacks.html

问题 What operation does the following ‘C’ statement perform? star = star ^ 0b00100100; (A) Toggles bits 2 and 5 of the variable star. (B) Clears all bits except bits 2 and 5 of the variable star. (C) Sets all bits except bits 2 and 5 of the variable star. (D) Multiplies value in the variable star with 0b00100100. I'm still clueless about this. Can someone help me out? 回答1: XOR operator (also called "logical addition") is defined like this: a b a^b ----------- 0 0 0 0 1 1 1 0 1 1 1 0 So a^0 leaves

问题 What operation does the following ‘C’ statement perform? star = star ^ 0b00100100; (A) Toggles bits 2 and 5 of the variable star. (B) Clears all bits except bits 2 and 5 of the variable star. (C) Sets all bits except bits 2 and 5 of the variable star. (D) Multiplies value in the variable star with 0b00100100. I'm still clueless about this. Can someone help me out? 回答1: XOR operator (also called "logical addition") is defined like this: a b a^b ----------- 0 0 0 0 1 1 1 0 1 1 1 0 So a^0 leaves

问题 This question already has answers here : Difference between >>> and >> (7 answers) Closed 2 years ago . I'm without my Java reference book and I'm having a tough time finding an answer with Google. What is the difference between the ">>" and ">>>" operators in Java? int value = 0x0100; int result = (value >> 8); System.out.println("(value >> 8) = " + result); // Prints: "(value >> 8) = 1" result = (value >>> 8); System.out.println("(value >>> 8) = " + result); // Prints: "(value >>> 8) = 1"

问题 Which is the simplest way to check if two integers have same sign? Is there any short bitwise trick to do this? 回答1: Here is a version that works in C/C++ that doesn't rely on integer sizes or have the overflow problem (i.e. x*y>=0 doesn't work) bool SameSign(int x, int y) { return (x >= 0) ^ (y < 0); } Of course, you can geek out and template: template <typename valueType> bool SameSign(typename valueType x, typename valueType y) { return (x >= 0) ^ (y < 0); } Note: Since we are using

问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 6 years ago . I have a 32-bit number and without using for loop, I want to set m bit to n bits. For example: m bit may be 2nd or 5th or 9th or 10th . n bit may be 22nd

问题 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). 回答1: Javascript represents all numbers as 64-bit double precision IEEE 754 floating point numbers (see the ECMAscript spec, section 8.5.) All positive integers up to 2^53 can be encoded precisely. Larger integers get their least significant bits clipped. This leaves the question of how can

问题 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). 回答1: Javascript represents all numbers as 64-bit double precision IEEE 754 floating point numbers (see the ECMAscript spec, section 8.5.) All positive integers up to 2^53 can be encoded precisely. Larger integers get their least significant bits clipped. This leaves the question of how can

问题 I recently picked up a copy of Applied Cryptography by Bruce Schneier and it's been a good read. I now understand how several algorithms outlined in the book work, and I'd like to start implementing a few of them in C. One thing that many of the algorithms have in common is dividing an x-bit key, into several smaller y-bit keys. For example, Blowfish's key, X, is 64-bits, but you are required to break it up into two 32-bit halves; Xl and Xr. This is where I'm getting stuck. I'm fairly decent