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arsperger/get set bit

Created November 1, 2021 06:11
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  1. arsperger created this gist Nov 1, 2021.
    64 changes: 64 additions & 0 deletions get set bit
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    Let suppose few things first
    num = 55 Integer to perform bitwise operations (set, get, clear, toggle).
    n = 4 0 based bit position to perform bitwise operations.

    How to get a bit?
    To get the nth bit of num right shift num, n times. Then perform bitwise AND & with 1.
    bit = (num >> n) & 1;
    How it works?

    0011 0111 (55 in decimal)
    >> 4 (right shift 4 times)
    -----------------
    0000 0011
    & 0000 0001 (1 in decimal)
    -----------------
    => 0000 0001 (final result)
    How to set a bit?

    To set a particular bit of number. Left shift 1 n times. Then perform bitwise OR | operation with num.
    num |= (1 << n); // Equivalent to; num = (1 << n) | num;
    How it works?

    0000 0001 (1 in decimal)
    << 4 (left shift 4 times)
    -----------------
    0001 0000
    | 0011 0111 (55 in decimal)
    -----------------
    => 0001 0000 (final result)
    How to clear a bit?
    Left shift 1, n times i.e. 1 << n.
    Perform bitwise complement with the above result. So that the nth bit becomes unset and rest of bit becomes set i.e. ~ (1 << n).
    Finally, perform bitwise AND & operation with the above result and num. The above three steps together can be written as num & (~ (1 << n));
    Steps to clear a bit

    num &= (~(1 << n)); // Equivalent to; num = num & (~(1 << n));
    How it works?

    0000 0001 (1 in decimal)
    << 4 (left shift 4 times)
    -----------------
    ~ 0001 0000
    -----------------
    1110 1111
    & 0011 0111 (55 in decimal)
    -----------------
    => 0010 0111 (final result)
    How to toggle a bit?
    To toggle a bit we use bitwise XOR ^ operator. Bitwise XOR operator evaluates to 1 if corresponding bit of both operands are different, otherwise evaluates to 0.

    Which means to toggle a bit, we need to perform XOR operation with the bit you want to toggle and 1.

    num ^= (1 << n); // Equivalent to; num = num ^ (1 << n);
    How it works?

    If the bit to toggle is 0 then, 0 ^ 1 => 1.
    If the bit to toggle is 1 then, 1 ^ 1 => 0.
    0000 0001 (1 in decimal)
    << 4 (left shift 4 times)
    -----------------
    0001 0000
    ^ 0011 0111 (55 in decimal)
    -----------------
    => 0010 0111 (final result)