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Constraining Dynamic array size

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Hello All, I have a query in constraining the size of dynamic array. One way of constraining i have given bellow. class dynamic_array; rand int array_size; rand logic[7:0] data[]; constraint arry_constrian{ data.size() == array_size; } endclass In the above code there is a great possibilities that dynamic array might get generate first then array_size, in that case data size will be random. We can use solve before construct, but I am not sure how to use solve before construct for dynamic array. It would be good if i get some comments on the above. Sundar


Originally posted in cdnusers.org by sundar_80
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  • In SystemVerilog, a dynamic array marked with "rand" and its size are considered as two different random variables. In addition, an implicit ordering exists between generation of the size of a dynamic array and generation of that dynamic array, where the size variable is always generated first. In your examples, random variables "array_size" and "data.size()" are solved first and assigned random variables. Then random array "data" is resized to the value assigned to "data.size()" and then its members are randomized. This approach effectively means that size of array "data" in your example will always be the same as the random value generated for "array_size". Note that this implicit ordering is very important to keep in mind since it can lead to generation problems (i.e. not finding a solution where one exists) if a constraint is given between "array_size" and one of the elements of array "data" (e.g. data[3]). See section 12.3 in LRM.


    Originally posted in cdnusers.org by iman2418
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  • In SystemVerilog, a dynamic array marked with "rand" and its size are considered as two different random variables. In addition, an implicit ordering exists between generation of the size of a dynamic array and generation of that dynamic array, where the size variable is always generated first. In your examples, random variables "array_size" and "data.size()" are solved first and assigned random variables. Then random array "data" is resized to the value assigned to "data.size()" and then its members are randomized. This approach effectively means that size of array "data" in your example will always be the same as the random value generated for "array_size". Note that this implicit ordering is very important to keep in mind since it can lead to generation problems (i.e. not finding a solution where one exists) if a constraint is given between "array_size" and one of the elements of array "data" (e.g. data[3]). See section 12.3 in LRM.


    Originally posted in cdnusers.org by iman2418
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