Bit Manipulation - Bit Manipulation in The C Programming Language

Bit Manipulation in The C Programming Language

C has direct support for bitwise operations that can be used for bit manipulation. In the following examples, n is the index of the bit to be manipulated within the variable bit_fld, which is an unsigned char being used as a bit field. Bit indexing begins at 0, not 1. Bit 0 is the least significant bit.

Set a bit
bit_fld |= (1 << n)
Clear a bit
bit_fld &= ~(1 << n)
Toggle a bit
bit_fld ^= (1 << n)
Test a bit
bit_fld & (1 << n)

When using an array of bytes to represent set of bits, i.e., a bit array or bitset, the index of the byte in the array associated with a bit n can be calculated using division:

n / CHAR_BIT

where n is the index of the given bit and CHAR_BIT gives the number of bits in a C char.

The index of the bit within the byte indexed by the above can be calculated via a modulo operation:

n % CHAR_BIT

(Note: unsigned char is typically used in C to represent a byte and CHAR_BIT is most often 8 on modern processors. % is the C modulo operator.)

Read more about this topic:  Bit Manipulation

Famous quotes containing the words bit, manipulation, programming and/or language:

    Perhaps he was a bit different from other people, but what really sympathetic person is not a little mad?
    Isadora Duncan (1878–1927)

    The basic tool for the manipulation of reality is the manipulation of words. If you can control the meaning of words, you can control the people who must use the words.
    Philip K. Dick (1928–1982)

    If there is a price to pay for the privilege of spending the early years of child rearing in the driver’s seat, it is our reluctance, our inability, to tolerate being demoted to the backseat. Spurred by our success in programming our children during the preschool years, we may find it difficult to forgo in later states the level of control that once afforded us so much satisfaction.
    Melinda M. Marshall (20th century)

    If when a businessman speaks of minority employment, or air pollution, or poverty, he speaks in the language of a certified public accountant analyzing a corporate balance sheet, who is to know that he understands the human problems behind the statistical ones? If the businessman would stop talking like a computer printout or a page from the corporate annual report, other people would stop thinking he had a cash register for a heart. It is as simple as that—but that isn’t simple.
    Louis B. Lundborg (1906–1981)