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Algorithmically modifying data below the word level

Bit manipulation is the act of algorithmically manipulating bits or other pieces of data shorter than a word. Computer programming tasks that require bit manipulation include low level device control, error detection and correction algorithms, data compression, encryption algorithms, and optimization. For most other tasks, modern programming languages allow the programmer to work directly with abstractions instead of bits that represent those abstractions. Source code that does bit manipulation makes use of the bitwise operations: AND, OR, XOR, NOT, and possibly other operations analogous to the boolean operators; there are also bit shifts and operations to count ones and zeros, find high and low one or zero, set, reset and test bits, extract and insert fields, mask and zero fields, gather and scatter bits to and from specified bit positions or fields. Integer arithmetic operators can also effect bit operations in conjunction with the other operators. Bit manipulation, in some cases, can obviate or reduce the need to loop over a data structure and can give manyfold speed ups, as bit manipulations are processed in parallel.

Bit twiddling, bit fiddling, bit bashing, and bit gymnastics are often used interchangeably with bit manipulation, but sometimes exclusively refer to clever or non obvious ways or uses of bit manipulation, or tedious or challenging low level device control data manipulation tasks. The term bit twiddling dates from early computing hardware, where computer operators would make adjustments by tweaking or twiddling computer controls. As computer programming languages evolved, programmers adopted the term to mean any handling of data that involved bit level computation.

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 central processing unit (CPU), and is used to manipulate values for comparisons and calculations. On most processors, the majority of bitwise operations are single cycle substantially faster than division and multiplication and branches. While modern processors usually perform some arithmetic and logical operations just as fast as bitwise operations due to their longer instruction pipelines and other architectural design choices, bitwise operations do commonly use less power because of the reduced use of resources.

A mask is data that is used for bitwise operations, particularly in a bit field. Using a mask, multiple bits in a Byte, nibble, word (etc.) can be set either on, off or inverted from on to off (or vice versa) in a single bitwise operation. More comprehensive applications of masking, when applied conditionally to operations, are termed predication.