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- Bitwise operation
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- C (programming language)
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- How to perform a bitwise operation on floating point numbers
- c - Are the results of bitwise operations on signed integers defined ...
- c++ - Performance wise, how fast are Bitwise Operators vs.
- c - Implementing if - else if using bitwise operators - Stack Overflow
- c - How to implement Bitcount using only Bitwise operators?
- What are bitwise shift (bit-shift) operators and how do they work?
- c++ - How to set, clear, and toggle a single bit - Stack Overflow
- Most common C# bitwise operations on enums - Stack Overflow
- c - Bitwise operators and "endianness" - Stack Overflow
- objective c - Understanding the bitwise AND Operator - Stack …
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In the C programming language, operations can be performed on a bit level using bitwise operators.
Bitwise operations are contrasted by byte-level operations which characterize the bitwise operators' logical counterparts, the AND, OR, NOT operators. Instead of performing on individual bits, byte-level operators perform on strings of eight bits (known as bytes) at a time. The reason for this is that a byte is normally the smallest unit of addressable memory (i.e. data with a unique memory address).
This applies to bitwise operators as well, which means that even though they operate on only one bit at a time they cannot accept anything smaller than a byte as their input.
All of these operators are also available in C++, and many C-family languages.
Bitwise operators
C provides six operators for bit manipulation.
= Bitwise AND &
=The bitwise AND operator is a single ampersand: &. It is just a representation of AND which does its work on the bits of the operands rather than the truth value of the operands. Bitwise binary AND performs logical conjunction (shown in the table above) of the bits in each position of a number in its binary form.
For instance, working with a byte (the char type):
11001000
& 10111000
--------
= 10001000
The most significant bit of the first number is 1 and that of the second number is also 1 so the most significant bit of the result is 1; in the second most significant bit, the bit of second number is zero, so we have the result as 0.
= Bitwise OR |
=Similar to bitwise AND, bitwise OR performs logical disjunction at the bit level. Its result is a 1 if either of the bits is 1 and zero only when both bits are 0. Its symbol is | which can be called a pipe.
= Bitwise XOR ^
=The bitwise XOR (exclusive or) performs an exclusive disjunction, which is equivalent to adding two bits and discarding the carry. The result is zero only when we have two zeroes or two ones. XOR can be used to toggle the bits between 1 and 0. Thus i = i ^ 1 when used in a loop toggles its values between 1 and 0.
Shift operators
There are two bitwise shift operators. They are
Right shift (>>)
Left shift (<<)
= Right shift >>
=The symbol of right shift operator is >>. For its operation, it requires two operands. It shifts each bit in its left operand to the right.
The number following the operator decides the number of places the bits are shifted (i.e. the right operand).
Thus by doing ch >> 3 all the bits will be shifted to the right by three places and so on.
However, do note that a shift operand value which is either a negative number or is greater than or equal to the total number of bits in this value results in undefined behavior. For example, when shifting a 32 bit unsigned integer, a shift amount of 32 or higher would be undefined.
Example:
If the variable ch contains the bit pattern 11100101, then ch >> 1 will produce the result 01110010, and ch >> 2 will produce 00111001.
Here blank spaces are generated simultaneously on the left when the bits are shifted to the right. When performed on an unsigned type or a non-negative value in a signed type, the operation performed is a logical shift, causing the blanks to be filled by 0s (zeros). When performed on a negative value in a signed type, the result is technically implementation-defined (compiler dependent), however most compilers will perform an arithmetic shift, causing the blank to be filled with the set sign bit of the left operand.
Right shift can be used to divide a bit pattern by 2 as shown:
Right shift operator usage
Typical usage of a right shift operator in C can be seen from the following code.
Example:
The output of the above program will be
= Left shift <<
=The symbol of left shift operator is <<. It shifts each bit in its left-hand operand to the left by the number of positions indicated by the right-hand operand. It works opposite to that of right shift operator. Thus by doing ch << 1 in the above example (11100101) we have 11001010.
Blank spaces generated are filled up by zeroes as above.
However, do note that a shift operand value which is either a negative number or is greater than or equal to the total number of bits in this value results in undefined behavior. This is defined in the standard at ISO 9899:2011 6.5.7 Bit-wise shift operators. For example, when shifting a 32 bit unsigned integer, a shift amount of 32 or higher would be undefined.
Left shift can be used to multiply an integer by powers of 2 as in
Example: a simple addition program
The following program adds two operands using AND, XOR and left shift (<<).
Bitwise assignment operators
C provides a compound assignment operator for each binary arithmetic and bitwise operation. Each operator accepts a left operand and a right operand, performs the appropriate binary operation on both and stores the result in the left operand.
The bitwise assignment operators are as follows.
Logical equivalents
Four of the bitwise operators have equivalent logical operators. They are equivalent in that they have the same truth tables. However, logical operators treat each operand as having only one value, either true or false, rather than treating each bit of an operand as an independent value. Logical operators consider zero false and any nonzero value true. Another difference is that logical operators perform short-circuit evaluation.
The table below matches equivalent operators and shows a and b as operands of the operators.
!= has the same truth table as ^ but unlike the true logical operators, by itself != is not strictly speaking a logical operator. This is because a logical operator must treat any nonzero value the same. To be used as a logical operator != requires that operands be normalized first. A logical not applied to both operands will not change the truth table that results but will ensure all nonzero values are converted to the same value before comparison. This works because ! on a zero always results in a one and ! on any nonzero value always results in a zero.
Example:
The output of the above program will be
See also
Bit manipulation
Bitwise operation
Find first set
Operators in C and C++
Bitboard
Boolean algebra (logic)
XOR swap algorithm
XOR linked list
References
External links
Bitwise Operators
Demystifying bitwise operations, a gentle C tutorial
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Daftar Isi
How to perform a bitwise operation on floating point numbers
Apr 2, 2017 · Bitwise operations in C/C++ work on value-representation of a number. And the value-representation of floating point numbers is not defined in C/C++ (unsigned integers are an exception in this regard, as their shift is defined as-if they are stored in 2's complement).
c - Are the results of bitwise operations on signed integers defined ...
By the way, note that per 6.2.6.1, negative zero, if it exists, is required to behave identically to ordinary zero as an operand to bitwise operations: Where an operator is applied to a value that has more than one object representation, which object representation is used shall not affect the value of the result. –
c++ - Performance wise, how fast are Bitwise Operators vs.
Dec 5, 2013 · Bitwise operations are much faster. This is why the compiler will use bitwise operations for you. Actually, I think it will be faster to implement it as: ~i & 1 Similarly, if you look at the assembly code your compiler generates, you may see things like x ^= x instead of x=0. But (I hope) you are not going to use this in your C++ code.
c - Implementing if - else if using bitwise operators - Stack Overflow
Jun 2, 2013 · Assume that the value of test is 1 or 0. Here I can implement the following if statement using bitwise operators as below.
c - How to implement Bitcount using only Bitwise operators?
The task is to implement a bit count logic using only bitwise operators. I got it working fine, but am wondering if someone can suggest a more elegant approach. Only Bitwise ops are allowed. No "...
What are bitwise shift (bit-shift) operators and how do they work?
The Bitwise operators are used to perform operations a bit-level or to manipulate bits in different ways. The bitwise operations are found to be much faster and are some times used to improve the efficiency of a program. Basically, Bitwise operators can be applied to the integer types: long, int, short, char and byte. Bitwise Shift Operators
c++ - How to set, clear, and toggle a single bit - Stack Overflow
Use the bitwise AND operator (&) to set the nth bit of number to 0. inline Uint bit_clear(Uint number, Uint n) { return number & ~((Uint)1 << n); } You must invert the bit string with the bitwise NOT operator (~), then AND it. Toggling a bit. Use the …
Most common C# bitwise operations on enums - Stack Overflow
Sep 18, 2008 · .NET's built-in flag enum operations are unfortunately quite limited. Most of the time users are left with figuring out the bitwise operation logic. In .NET 4, the method HasFlag was added to Enum which helps simplify user's code but unfortunately there are many problems with it.
c - Bitwise operators and "endianness" - Stack Overflow
Jun 25, 2009 · @JoshC: (cont.) And in C, the bit shift operators are defined in a way that abstracts them even more: they are defined in terms of the values they produce, not in terms of the way they move the underlying bits around (so if you're on some obscure platform where a hardware bit-shift instruction would produce an invalid bit layout, e.g. you've shifted a value bit into a …
objective c - Understanding the bitwise AND Operator - Stack …
Aug 7, 2010 · The Bitwise AND Operator. Bitwise ANDing is frequently used for masking operations. That is, this operator can be used easily to set specific bits of a data item to 0. For example, the statement. w3 = w1 & 3; assigns to w3 the value of …