Things about data storage 2

Part1： Original code , Inverse code , Complement code Signed number ？ Sign bit Value bits integer

According to what rules is the data stored in the computer ？ So let's see , Original code , Inverse code , Complement code .

According to the definition, the negative integer original code with sign, the inverse code and complement are different , Unsigned and positive numbers are the same .

The first bit is the sign bit , It's all used 0 Express positive ,1 Negative . The numerical digits are all different

Part2：-10 Integers Complement code Why? adder Unification of addition and subtraction

Let's give you an example int：-10, We know that an integer occupies 4 Bytes

00000000 00000000 00000000 00000000; empty ： The general situation is not 0

10000000 00000000 00000000 00001010; Original code

11111111 11111111 11111111 11110101; Inverse code

11111111 11111111 11111111 11110110; Complement code

ff ff ff f6; Hexadecimal representation

In the computer , Integer data is represented by hexadecimal complement

Why do this ？

This is related to the structure of the computer , As I thought before , Use signals to represent the form of numbers , These figures will be used after all , The basic algorithm between numbers , How to realize addition and subtraction , It's easy to think about it with us 1+1, be equal to 2, How to add and subtract in the computer ？

Add , Before learning the principles of computer composition , First we know that addition is the addition of signals at two positions , Use a component , When both are 1 If yes, it becomes 0, At the same time, the latter one becomes 1（0） Or 0（1）. What about subtraction 1 become 0,0 become 1 Do you ？ This is the same as addition ？ How to distinguish ？ In those days , When the complement of the original code has not appeared , To solve this problem , Someone put forward the concept of original code, inverse code and complement , a pile 101010 Explore , Now it seems very reasonable , Know this rule , It's a bit like the Berlin Wall . The existence of complement allows subtraction to do addition .

Part3：

Large and small end Memory block Low address Pattern The way Byte order

When we are opening up space , The opened space is called memory block , By number , It has high address side and low address side , The same data 0x11223344,0x High position … status .

We put it in memory block in bytes , Obviously, there are many sorting methods , The two most used methods are to put the high address in the low place , Low address to high and high address to high , Put the low address low , Two ways , The former is called big end mode , The latter is called small end mode . Because it is put in bytes , There is the word byte order .

Part4：

char  %d Improve the overall shape %u

It was said before char Type can be put into integer , but char It takes only one byte , When an integer data is put into char In the middle of the day , Press 32 Bits are first converted to complements , Only the last byte put in is the low byte . When char To use %d When the output , We need to improve the integer first , If the first one is 1, Make up 1 To 32 position , if 0 Then fill 0（ Only negative integers complement 1, Because its original code, inverse code and complement are different ）

%u It's an unsigned integer , Judge before complement conversion （ After integer lifting ）

Part5：

char Range Complement code With or without symbols repair 1000 0000 circle +1 Change sign 128

char Types are divided into signed and unsigned , It is also stored in memory in the form of complement 、

The signed range is ·-128—>127：01111111（127）+1=10000000（-128）

The unsigned range is 0à255：00000000（0）à11111111(255)

We know that the complement in memory needs to be reduced by one , But symbolic ·10000000 It will automatically convert here -128. And because of the complement , ad locum 127+1=-128.