Detailed introduction to PHP's clever use of bit operations to achieve website permission management

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First of all, let's define 4 constants to set four permissions:

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define(ADD,1);//Increase the permissions of database records
define(UPD,2);//Modify the permissions of database records
define(SEL ,4);//Permission to search database records
define(DEL,8);//Permission to delete database records

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Next Assume there are 3 users:

User A has four permissions ADD-UPD-SEL-DEL. Use bitwise OR operation to calculate the total value of A's permissions
$a_ all=ADD|UPD|SEL|DEL;//$all=15 You can notice that this value is the same as the result of addition
B user has the three permissions of ADD-UPD-SEL, use Bitwise OR operation calculates the total value of B's ​​permissions
$b_all=ADD|UPD|SEL;//$all=7 This value is the same as the result of addition
User C has two permissions, ADD-UPD. Use bitwise OR operation to calculate the total permission value of C
$c_all=ADD|UPD;//$all=3 This value is still the same as the result of addition

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Next we use Bitwise AND operation
$a_all&ADD The result is true
$a_all&UPD The result is true
$a_all&SEL The result is true
$a_all&DEL The result is true

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$b_all&ADD The result is true
$b_all&UPD The result is true
$b_all&SEL The result is true
$b_all&DEL The result is false

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$ c_all&ADD returns true$c_all&UPD returns true
$c_all&SEL returns false
$c_all&DEL returns false

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Have you discovered the secret?

1. When the total value of permissions is ANDed with the permission that does not exist, the result is false

2. The values ​​of permissions are all Power of 2

After knowing these two points of permission processing, it becomes simple. Just add the total value of the user's current permissions and the current value every time an operation involving permissions is performed. The permissions required for the operation are bitwise ANDed. If the result is true, execute it, and if it is false, just report an error (of course, it does not necessarily report an error, you can design your own program when you don't have permission).

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