Constraint Puzzles

Q: Generate an array of size 10 with unique values between 0 and 100, WITHOUT using the `unique` constraint.

rand bit [7:0] arr[10];
constraint c_unique_manual {
    foreach (arr[i])
        foreach (arr[j])
            if (i != j) arr[i] != arr[j];
}

Note: This is O(N^2) complexity, acceptable for small arrays only.

Used to change the probability distribution, NOT the solution space.

If `A` implies `B` (e.g., `A -> B==0`), randomizing them together might make `A=1` extremely rare. Using `solve A before B` forces the solver to pick A first, then pick B consistent with A. This makes `A=1` happen with 50% probability (if A is 1-bit).

Constraints declared with `soft` can be overridden by inline constraints (`with {}`) or extended class constraints without causing a conflict failure. If a conflict occurs, the soft constraint is discarded.

constraint c_len { soft len == 10; } // Can be overridden to 20 later

Q: Generate a bit 'b' that is 1 (70% prob) and 0 (30% prob) without using `dist`.

rand int temp;
rand bit b;
constraint c_dist { 
    temp inside {[0:99]};
    b == (temp < 70); 
}

Yes. `if (mode == 1) len == 10;` implies that if `len != 10`, `mode` CANNOT be 1.

The solver considers all active constraints simultaneously. It does not execute line-by-line like procedural code.

Use the `constraint_mode()` method on the handle.

pkt.c_len.constraint_mode(0); // Disable only 'c_len'
pkt.constraint_mode(0);       // Disable ALL constraints