How to use the negation operator in python

Python negation operator

~: Bitwise negation operator: negate each binary bit of the data, that is, turn 1 into 0, change 0 to 1.

~x is similar to -x-1

1, calculation basis

• ①The original code, inverse code and complement code of positive numbers are all The same

• ②The complement of a negative number is that the sign bit remains unchanged, the remaining bits are inverted and 1 is added

• ③The complement of the original code is found : Negate, 1

• ④ Complement to find the original code: Negate, 1

• ##⑤ Negative numbers are stored in complement

• ⑥The inversion operation is performed on the original code

• ⑦Sign bit, 1 represents a negative number, 0 represents a positive number

2. Example

~（-2）

First of all, you need to know the binary form of -2 in the computer. From ⑤ and ②, we can know:

• -2 Original code: 1000 0000 0000 0010

• -2 Negative code: 1111 1111 1111 1101 #The sign bit remains unchanged, please negate it

• -2's complement: 1111 1111 1111 1110 #Complement code = inverse code + 1

1111 1111 1111 1110 is the prototype of -2 in the computer

Now start to negate it, the sign bit remains unchanged,

bitwise negation: 0000 0000 0000 0001

is obviously a positive number , its original code is itself, so the output is 1.

~2

2 Original code, inverse code, complement code: 0000 0000 0000 0010

Bitwise negation: 1111 1111 1111 1101

What should I do if this is a negative number? Can I ask directly?

Obviously this is not possible, ⑥ said: the negation operation calculation result is performed on the original code, ⑤ also said: negative numbers are stored in complement code

1111 1111 1111 1101 It is the complement of 0000 0000 0000 0010, but what we want is the result, not the prototype in the computer,

is just right, ④ complement to find the original code: negate, 1

• Negate: 1000 0000 0000 0010

• Add 1: 1000 0000 0000 0011

So, we get the original code, you can calculate the result

1000 0000 0000 0011 = -3

In short, inversion is very simple, but you must pay attention to whether the inversion is the original code and whether the result can be calculated directly

Python numerical inversion problem~

In python, using the inversion symbol~ does not get the result we imagined. To sum up the rules, it is (the inverted value) = - (Value before inversion) -1

Let’s analyze it

For example, if 1 is inverted, the 8-bit binary representation of 1 is: 0000 0001, and the result after inversion is: 1111 1110, for computers, binary numbers starting with 1 represent negative numbers, so what exactly does 1111 1110 represent as a negative value? If you want to know this value, you can find its complement, that is, first take the complement: 0000 0001, Add 1:0000 0010, indicating that the original code of 1111 1110 is 0000 0010, which is a positive number 2, so 1111 1110 represents a negative number -2

Here is another example

Yes- 2 is inverted. The binary representation of -2 is the complement of 2, that is, 0000 0010 > 1111 1101 > 1111 1110. The binary representation of -2 is 1111 1110. Inverting it gives 0000 0001. Obviously, after inverting The value of is 1, so ~(-2)=1, ~1=-2

The summary is: (value after negation) = -(value before negation)-1

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