.. _arduino-bitwisecompound:
compound bitwise AND (&=), compound bitwise OR (\|=)
====================================================
The compound bitwise operators perform their calculations at the
bit level of variables. They are often used to clear and set
specific bits of a variable.
See the
`bitwise AND (&) <http://arduino.cc/en/Reference/BitwiseAnd>`_ and
`bitwise OR (\|) <http://arduino.cc/en/Reference/BitwiseAnd>`_
operators for the details of their operation, and also the
`Bitmath Tutorial <http://www.arduino.cc/playground/Code/BitMath>`_
for more information on bitwise operators.
compound bitwise AND (&=)
=========================
Description
-----------
The compound bitwise AND operator (&=) is often used with a
variable and a constant to force particular bits in a variable to
the LOW state (to 0). This is often referred to in programming
guides as "clearing" or "resetting" bits.
Syntax:
-------
::
x &= y; // equivalent to x = x & y;
Parameters
----------
x: a char, int or long variable
y: an integer constant or char, int, or long
Example:
--------
First, a review of the Bitwise AND (&) operator
::
0 0 1 1 operand1
0 1 0 1 operand2
----------
0 0 0 1 (operand1 & operand2) - returned result
Bits that are "bitwise ANDed" with 0 are cleared to 0 so, if myByte
is a byte variable,
``myByte & B00000000 = 0;``
Bits that are "bitwise ANDed" with 1 are unchanged so,
``myByte & B11111111 = myByte;``
Note: because we are dealing with bits in a bitwise operator - it
is convenient to use the binary formatter with
`constants. <http://arduino.cc/en/Reference/IntegerConstants>`_ The
numbers are still the same value in other representations, they are
just not as easy to understand. Also, B00000000 is shown for
clarity, but zero in any number format is zero (hmmm something
philosophical there?)
Consequently - to clear (set to zero) bits 0 & 1 of a variable,
while leaving the rest of the variable unchanged, use the compound
bitwise AND operator (&=) with the constant B11111100
::
1 0 1 0 1 0 1 0 variable
1 1 1 1 1 1 0 0 mask
----------------------
1 0 1 0 1 0 0 0
variable unchanged
bits cleared
Here is the same representation with the variable's bits replaced
with the symbol x
::
x x x x x x x x variable
1 1 1 1 1 1 0 0 mask
----------------------
x x x x x x 0 0
variable unchanged
bits cleared
So if:
::
myByte = 10101010;
myByte &= B1111100 == B10101000;
compound bitwise OR (\|=)
=========================
Description
-----------
The compound bitwise OR operator (\|=) is often used with a
variable and a constant to "set" (set to 1) particular bits in a
variable.
Syntax:
-------
::
x |= y; // equivalent to x = x | y;
Parameters
----------
x: a char, int or long variable
y: an integer constant or char, int, or long
Example:
--------
First, a review of the Bitwise OR (\|) operator
::
0 0 1 1 operand1
0 1 0 1 operand2
----------
0 1 1 1 (operand1 | operand2) - returned result
Bits that are "bitwise ORed" with 0 are unchanged, so if myByte is
a byte variable,
myByte \| B00000000 = myByte;
Bits that are "bitwise ORed" with 1 are set to 1 so:
myByte & B11111111 = B11111111;
Consequently - to set bits 0 & 1 of a variable, while leaving the
rest of the variable unchanged, use the compound bitwise AND
operator (&=) with the constant B00000011
::
1 0 1 0 1 0 1 0 variable
0 0 0 0 0 0 1 1 mask
----------------------
1 0 1 0 1 0 1 1
variable unchanged
bits set
Here is the same representation with the variables bits replaced
with the symbol x
::
x x x x x x x x variable
0 0 0 0 0 0 1 1 mask
----------------------
x x x x x x 1 1
variable unchanged
bits set
So if:
::
myByte = B10101010;
myByte |= B00000011 == B10101011;
See Also
- `& <http://arduino.cc/en/Reference/BitwiseAnd>`_ (bitwise AND)
- `\| <http://arduino.cc/en/Reference/BitwiseAnd>`_ (bitwise OR)
- `&& <http://arduino.cc/en/Reference/Boolean>`_ (Boolean AND)
- `\|\| <http://arduino.cc/en/Reference/Boolean>`_ (Boolean OR)