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
- Clear a bit
- Toggle a bit
- Test a bit
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:
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.)
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