C-Language bitwise operators

C language has the features of high-level language and low-level language.

The so-called bitwise operation refers to the operation of bits.

Bit operations provided by the C language:

operator meaning
& Bitwise AND
| Bitwise OR
∧ Bitwise XOR OR
∽ Reverse
<< left Shift
>> Right Shift

Description

1. The bitwise operator, except for ∽, is a two-mesh (unary) operator, which requires an operand on each side.

2, the calculation can only be shaped or character data, can not be real data.

Bitwise-AND operator (&)

The provisions are as follows:

0&0=0 0&1=0 1&0=0 1&1=1

Example: 3&5=?
First, 3 and 5 in the complement, then the bitwise AND operation.

Complement of 3:00000011
Complement of 5:00000101

&: 00000001

3&5=1

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Bitwise OR operator (|)

The provisions are as follows:

0|0=0 0|1=1 1|0=1 1|1=1

Example: 060|017=?
Bitwise OR operation of octal number 60 and octet 17.

060 00110000
017 00001111

|: 00111111

060|017=077

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The XOR operator (∧), also known as the XOR operator

The provisions are as follows:

0∧0=0 0∧1=1 1∧0=1 1∧1=0

Example: 57∧42=?
The decimal number 57 and the decimal number 42 are bitwise XOR.

57 00111001
42 00101010

∧: 00010011

57∧42=19

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"Inverse" operator (∽)

The provisions are as follows:

∽0=1∽1=0

Example: ∽025=?
Bitwise negation of octal number 25 (that is, binary 0000000000010101).

0000000000010101
↓
1111111111101010

∽025=177752

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Left shift operator (<<)

　

A number of the binary all shifted left several bits, if the high-left after overflow, then discard, does not work.

Example: a=a<<2
Move the binary number of a to the left by 2 bits and the right to 0.
If a=15, which is the binary number 00001111, then

A 00001111
↓↓
A<<1 00011110
↓↓
A<<2 00111100

Last a=60

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Right shift operator (>>)

　

Move the binary of a number to the right of a number of bits, and the low move out of the part discard.

Example: a=a>>2
Shift the binary number of a to the right by 2 bits and left to 0.
If a=15, which is the binary number 00001111, then

A 00001111
↓↓
A>>1 00000111
↓↓
A>>2 00000011

Last A=3

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Bitwise operators combine with assignment operators to make an extended assignment operator

such as: &=,|=,>>=,<<=,∧=

Example: a&=b equivalent to A=a&b

a<<=2 equivalent to A=a<<2

Bit operations with different lengths of data

If two data lengths are different (for example, long and int) for bitwise operations (such as A&b, and A is long and b is int), the system aligns the two on the right. If B is positive, the left 16 bits fill 0. If B is negative, the left should fill 1. If B is an unsigned integer type, the left end is filled with 0.

Bit Operation example
Example: Take an integer A from the right end of the 4∽7 bit

Consider the following: 1, first a right shift 4 bits, namely A>>4

2, set a low 4-bit all 0 of the number, namely ∽ (∽0<<4)

3, the above two-type and operation, namely A>>4&∽ (∽0<<4)

The procedure is as follows:

Main ()

{unsigned a,b,c,d;

scanf ("%o", &a);

b=a>>4;

C=∽ (∽0<<4);

d=b&c;

printf ("%o\n%o\n", A, b);

}

Results: 331

331 (value of a, octal)

(Value of D, octal)

Example: cyclic displacement. A right loop shift is required for a. That is, a right loop shifts n bits, moving the original left (16-n) bit in a to the right n bits. Now assume that two bytes holds an integer. As pictured on the right.

Consider the following: 1, first put a right side n bit into the high n bit in B, namely:b=a<< (16-N)

2, will a right shift n bit, its left high N-bit 0, that is c=a>>n

3, the C and B bitwise OR operation, that is c=c|b

The procedure is as follows:

Main ()

{unsigned a,b,c;int N:

scanf ("a=%o,n=%d", &a,&n);

b=a<< (16-N);

c=a>>n;

c=c|b;

printf ("%o\n%o", a,c);

}

Results: a=157653,n=3

331 (value of a, octal)

(Value of D, octal)

Bit segment
A so-called bit segment is a member of a struct type that defines the length in bits.

Example: struct packed-data

{unsigned a:2;

unsigned b:6;

unsigned c:4;

unsigned d:4;

int i;

}data;

C-Language bitwise operators