Cours Programmation (b-a ba)
Get flash to fully experience Pearltrees
Puzzle : Devise a fast algorithm for computing the number of 1-bits in an unsigned integer. If the machine supports n-bit integers, can we compute the number of 1-bits in O(log n) machine instructions? Can we compute the number of 1-bits in O(b) machine instructions where b is the number of 1-bits in the integer? int bitcount (unsigned int n) { Iterated Count runs in time proportional to the total number of bits. It simply loops through all the bits, terminating slightly earlier because of the while condition.
Fast Bit Counting
Bitwise operation - Wikipedia, the free encyclopedia
A bitwise operation operates on one or more bit patterns or binary numerals at the level of their individual bits . It is a fast, primitive action directly supported by the processor , and is used to manipulate values for comparisons and calculations. On simple low-cost processors, typically, bitwise operations are substantially faster than division, several times faster than multiplication, and sometimes significantly faster than addition. While modern high-performance processors usually perform addition and multiplication as fast as bitwise operations, [ 1 ] the latter may still be optimal for overall power/performance due to lower resource use.