# Generate a Valid Phone Number Using SystemVerilog Constraints

Hi, today I would like to talk about how to use SystemVerilog constraints to generate some valid phone numbers. So the valid phone number formats are listed below:

1. Front Desk Operator Number:0
2. Emergency Number: 911
3. Local Phone Number (No Area Code): XXX-XXXX
4. Non-Local Phone Number: 1-XXX-XXX-XXXX

Those four types of phone numbers follow the distribution of 1:1:4:4.

For the distribution, it’s apparent that we can use dist in SystemVerilog to generate distributed weight constraints. We can typedef an enum number for our phone number types. Then the phone number type variable should follow the distribution above.

For the phone number, we need to have a rand variable which is within the range of 0 and 19,999,999,999. This gives us the length of the rand bit, 35, because 19,999,999,999 is between 2^34 and 2^35.

Then we can just use the implication operator to write the second constraint. There is one trick here. For the non-local phone number, since it’s over 32 bit long. We need to specify the length of the number in the constraint to guarantee the correct result. So we can code as follows:

class C;

typedef enum bit [1:0] {Operator, Emergency, Local, Non_Local} num_type_e; //create an enum type for phone number type

rand num_type_e num_type;

rand bit [34:0] val; // 35 bit wide

//weight distribution
constraint c1 {

num_type dist {Operator:=1, Emergency:=1, Local:=4, Non_Local:=4};

}

//constraints for each type of phone numbers
constraint c2 {

(num_type == Operator) -> val == 0; //implication operator

(num_type == Emergency) -> val == 911;

(num_type == Local) -> val inside{[1:910],[912:999_9999]};

(num_type == Non_Local) -> val inside{[35'd1_000_000_0000: 35'd1_999_999_9999]}; //35 bit specified

}

endclass

That’s all about how to generate some valid phone numbers. Special thanks to Chris and Morris for your help. Let me know if you have any questions.

## 3 thoughts on “Generate a Valid Phone Number Using SystemVerilog Constraints”

1. ayush bhesaniya says:

Hi,

I liked the way you coded , same constraint was asked in APPLE for design verification interview.
Keep Doing , Love to the point coding and explanation.

1. Yue Guo says:

Thank you for your encouragement! Good luck!

2. Rejila says:

Good questions with the code