The computer storage form and the binary conversion

Because the computer can recognize a binary sequence, the computer stores a number in binary form. For a positive number, store it in the form of the original code. For negative numbers, it is stored in the form of complement.

The original code of the positive number, the inverse code, the same complement:

Example: 1

Original code: 00000000 00000000 00000000 00000001

Reverse code: 00000000 00000000 00000000 00000001

Complement: 00000000 00000000 00000000 00000001

Negative numbers: Negative numbers are stored in the form of complement (the highest bit is the sign bit, 1 is negative, 0 is positive)

Example:-1

Original code: 10000000 00000000 00000000 00000001

Anti-code: 11111111 11111111 11111111 11111110 (the sign bit is unchanged, the remaining bits are reversed)

Complement: 11111111 11111111 11111111 11111111 (original code inversion plus one)

Small end: because the smallest unit of computer storage is bytes, and one byte is 8 bit bits, we represent the integer 4 bytes of 1 as: XX

Example: 1

Big- endian form: XX

Small End form: XX

Usually we write with a big-endian form, and the computer is stored with small-end storage, we can verify:

union b{                  int a;                  char b;}; Int main () {                  union B A;                 A.a = 1;                 printf (  "%c\n", a.b);                 system (  "pause");                 return 0;} 

In the form of small-end storage, the output should be a value of ASCII code 1.

Binary and Decimal conversions:

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>> Right Shift: binary right shift, positive words empty out of the complement 0;

Example: 7>>2=1 (note can not be written as 7<<-2, here is the wrong form)

00000000 00000000 00000000 00000111

00000000 00000000 00000000 00000001

<< left Shift: empty bit complement 0

Example:4<<1=8;

00000000 00000000 00000000 00000100

00000000 00000000 00000000 00001000

Arithmetic shift and logical shift:

There is only one case to consider when the negative is shifted right: because the highest bit of the negative number is the sign bit, when you move to the right, the vacated bit is 0 or 1.

Arithmetic shift: an empty bit complement 1.

Logical shift: vacated bit complement 0.

Whether the arithmetic shift or the logical shift, depends on the computer platform, so when the negative number of the right shift, its program is not portable.

Bitwise AND: For each of the binary operations, the same as 1 is 1, otherwise 0;

Example 7&5=5

00000000 00000000 00000000 00000111

00000000 00000000 00000000 00000101

00000000 00000000 00000000 00000101

Bitwise OR: For each operation of the binary, at least one bit is 1 for 1, otherwise 0;

Example: 8|4=12

00000000 00000000 00000000 00001000

00000000 00000000 00000000 00000100

00000000 00000000 00000000 00001100

XOR: For each of the binary operations performed, the same is 0, the difference is 1;

Example: 7^4=3

00000000 00000000 00000000 00000111

00000000 00000000 00000000 00000100

00000000 00000000 00000000 00000011

Negation: For each operation of the binary, 1 change 0,0 to 1;

00000000 00000000 00011000 00000011

11111111 11111111 11100111 11111100

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The computer storage form and the binary conversion