bit-manipulation

Given an array of integers ,You have to find two elements whose XOR is maximum. There is naive approach --just by picking each element and xoring with other elements and then comparing the results to find the pair. Other than this ,Is there any efficient algorithm? templatetypedef I think I have an O(n lg U) algorithm for this, where U is the largest number. The idea is similar to user949300's, but with a bit more detail. The intuition is as follows. When you're XORing two numbers together, to get the maximum value, you want to have a 1 at the highest possible position, and then of the

Line 294 of java.util.Random source says if ((n & -n) == n) // i.e., n is a power of 2 // rest of the code Why is this? The description is not entirely accurate because (0 & -0) == 0 but 0 is not a power of two. A better way to say it is ((n & -n) == n) when n is a power of two, or the negative of a power of two, or zero. If n is a power of two, then n in binary is a single 1 followed by zeros. -n in two's complement is the inverse + 1 so the bits lines up thus n 0000100...000 -n 1111100...000 n & -n 0000100...000 To see why this work, consider two's complement as inverse + 1, -n == ~n + 1 n

I must say I have never had cause to use bitwise operators, but I am sure there are some operations that I have performed that would have been more efficiently done with them. How have "shifting" and "OR-ing" helped you solve a problem more efficiently? See the famous Bit Twiddling Hacks Most of the multiply/divide ones are unnecessary - the compiler will do that automatically and you will just confuse people. But there are a bunch of, 'check/set/toggle bit N' type hacks that are very useful if you work with hardware or communications protocols. Using bitwise operations on strings (characters)

My question is based on this post: Decimal to Binary and it's chosen solution. I can get the chosen answer code working, but it only works for 5 bits. How do I modify this code to work for larger numbers, say 8 bits? I tried just adjusting the character offset in the fist line from 5 to 8, but no success. void getBin(int num, char *str) { *(str+5) = '\0'; int mask = 0x10 << 1; while(mask >>= 1) *str++ = !!(mask & num) + '0'; } and test with the given code, again adjusting the 6 to 9 to match the function above: int main() { char str[6]; getBin(10, str); printf("%s\n", str); return 0; } but the

This question already has an answer here: Implementing Logical Right Shift in C 8 answers Right now I am reading the book Computer Systems : Programmer Perspective. One problem in the book says to perform a logical right shift on a signed integer, I can't figure out how to start on this. The following is the actual question from the book: Fill in code for the following C functions. Function srl performs a logical right shift using an arithmetic right shift (given by value xsra ), followed by other operations not including right shifts or division. Function sra performs an arithmetic right