diff options
Diffstat (limited to 'docs/source/lang/compoundbitwise.rst')
| -rw-r--r-- | docs/source/lang/compoundbitwise.rst | 231 |
1 files changed, 0 insertions, 231 deletions
diff --git a/docs/source/lang/compoundbitwise.rst b/docs/source/lang/compoundbitwise.rst deleted file mode 100644 index a4bbb24..0000000 --- a/docs/source/lang/compoundbitwise.rst +++ /dev/null @@ -1,231 +0,0 @@ -.. highlight:: cpp - -.. _lang-compoundbitwise: - -Compound Bitwise Operators (``&=``, ``|=``, ``^=``) -=================================================== - -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 :ref:`bitwise math tutorial <lang-bitwisemath>` for more -information on bitwise operators. - -.. contents:: Contents - :local: - -.. _lang-compoundbitwise-and: - -Compound bitwise AND (``&=``) ------------------------------ - -The compound bitwise AND operator ``&=`` is often used with a variable -and a constant to force particular bits in a variable to be zero. This -is often referred to in programming guides as "clearing" or -"resetting" bits. In a program, writing the line ``x &= y;`` is -equivalent to writing ``x = x & y;``. That is, the value of ``x`` -after the line will be equal to its old value bitwise ANDed with the -value of ``y``:: - - x &= y; // equivalent to x = x & y; - -You can use any integer variable for ``x`` (i.e., any variable of type -``int``, ``long``, ``char``, ``byte``, etc.). You can use either an -integer variable or any :ref:`integer value -<lang-constants-integers>` (like ``3`` or ``0x20``) for ``y``. - -Before doing an example of ``&=``, let's first review the Bitwise AND -(``&``) operator:: - - 0 0 1 1 operand1 - 0 1 0 1 operand2 - ---------- - 0 0 0 1 (operand1 & operand2) = result - -As shown above, bits that are "bitwise ANDed" with 0 become 0, while -bits that are "bitwise ANDed" with 1 are left unchanged. So, if ``b`` -is a ``byte`` variable, then ``b & B00000000`` equals zero, and ``b & -B11111111`` equals ``b``. - -.. _lang-compoundbitwise-binconst: - -.. note:: The above uses :ref:`binary constants - <lang-constants-integers-bin>`\ . The numbers are still the same - value in other representations, they just might not be as easy to - understand. - - Normally, in C and C++ code, :ref:`hexadecimal - <lang-constants-integers-hex>` or :ref:`octal - <lang-constants-integers-oct>` are used when we're interested in - an integer's bits, rather than its value as a number. - - While hexadecimal and octal literals might be harder to understand - at first, you should really take the time to learn them. They're - part of C, C++, and many other programming languages, while binary - constants are available only for compatibility with Arduino. - - Also, ``B00000000`` is shown for clarity, but zero in any number - format is zero. - -So, to clear (set to zero) bits 0 and 1 of a one-byte variable, while -leaving the rest of the variable's bits unchanged, use the compound -bitwise AND operator ``&=`` with the constant ``B11111100`` -(hexadecimal ``0xFC``\ ):: - - 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 - ^^^^^^^^^^^^^^^^ ^^^^ - unchanged 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 - ^^^^^^^^^^^^^^^^ ^^^^ - unchanged cleared - - -So, using a byte variable ``b``\ , if we say:: - - b = B10101010; // B10101010 == 0xAA - b &= B11111100; // B11111100 == 0xFC - -then we will have :: - - b == B10101000; // B10101000 == 0xA8 - -.. _lang-compoundbitwise-or: - -Compound bitwise OR (``|=``) ----------------------------- - -The compound bitwise OR operator ``|=`` is often used with a variable -and a constant to "set" (set to 1) particular bits in a variable. In -a program, writing the line ``x |= y;`` is equivalent to writing ``x = -x | y;``. That is, the value of ``x`` after the line will be equal to -its old value bitwise ORed with the value of ``y``:: - - x |= y; // equivalent to x = x | y; - -You can use any integer variable for ``x`` (i.e., any variable of type -``int``, ``long``, ``char``, ``byte``, etc.). You can use either an -integer variable or any integer value (like ``3`` or ``0x20``) for -``y``. (This works the same way as :ref:`compound bitwise AND -<lang-compoundbitwise-and>`\ , ``&=``). - -Before doing an example of ``|=``, let's first review the Bitwise OR -(``|``) operator:: - - 0 0 1 1 operand1 - 0 1 0 1 operand2 - ---------- - 0 1 1 1 (operand1 | operand2) = result - -Bits that are "bitwise ORed" with 0 are unchanged, while bits that are -"bitwise ORed" with 1 are set to 1. So if ``b`` is a ``byte`` -variable, then ``b | B00000000`` equals ``b``, and ``b & B11111111`` -equals ``B11111111`` (here we've used binary constants; see the -:ref:`note <lang-compoundbitwise-binconst>` above). - -So, to set bits 0 and 1 of a one-byte variable, while leaving the rest -of the variable unchanged, use the compound bitwise OR operator -(``|=``) with the constant ``B00000011`` (hexadecimal ``0x3``):: - - 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 - ^^^^^^^^^^^^^^^^ ^^^^ - unchanged set - -Here is the same representation with the variable's 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 - ^^^^^^^^^^^^^^^^ ^^^^ - unchanged set - -So, using a byte variable ``b``, if we say:: - - b = B10101010; // B10101010 == 0xAA - b |= B00000011; // B00000011 == 0x3 - -then we will have :: - - b == B10101011; // B10101011 == 0xAB - -.. _lang-compoundbitwise-xor: - -Compound bitwise XOR (``^=``) ------------------------------ - -The compound bitwise XOR operator ``^=`` is used with a variable and a -constant to "toggle" (change 0 to 1, and 1 to 0) particular bits in a -variable. In a program, writing the line ``x ^= y;`` is equivalent to -writing ``x = x ^ y;``. That is, the value of ``x`` after the line -will be equal to its old value bitwise XORed with the value of ``y``:: - - x ^= y; // equivalent to x = x ^ y; - -You can use any integer variable for ``x`` (i.e., any variable of type -``int``, ``long``, ``char``, ``byte``, etc.). You can use either an -integer variable or any integer value (like ``3`` or ``0x20``) for -``y``. (This works the same way as :ref:`&= -<lang-compoundbitwise-and>` and :ref:`\|= -<lang-compoundbitwise-or>`; in fact, these three operators all -work the same in this way). - -Before doing an example of ``^=``, let's first review the Bitwise -XOR operator, ``^``:: - - 0 0 1 1 operand1 - 0 1 0 1 operand2 - ---------- - 0 1 1 0 (operand1 ^ operand2) = result - -One way to look at bitwise XOR is that each bit in the result is a 1 -if the input bits are different, or 0 if they are the same. Another -way to think about it is that the result bit will be 1 when *exactly* -one (no more, no less) of the input bits is 1; otherwise, it will be -zero. This means that if you XOR a bit with 1, it will change (or -toggle) its value, while if you XOR a bit with 0, it stays the same. - -So, to toggle bits 0 and 1 of a one-byte variable, while leaving the -rest of the variable unchanged, use the compound bitwise XOR operator -``^=`` with the constant ``B00000011`` (hexadecimal ``0x3``\ ; see -:ref:`note <lang-compoundbitwise-binconst>` above):: - - 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 - ^^^^^^^^^^^^^^^^ ^^^^ - unchanged toggled - -So, using a byte variable ``b``, if we say:: - - b = B10101010; // B10101010 == 0xAA - b ^= B00000011; // B00000011 == 0x3 - -then we will have :: - - b == B10101001; // B10101001 == 0xA9 - -See Also --------- - -- :ref:`Boolean operations <lang-boolean>` (``&&``, ``||``) -- :ref:`Bitwise operators <lang-bitwisemath>` (``&``, ``|``, ``^``, ``~``) - - -.. include:: cc-attribution.txt |