Why does system verilog max() and min() functions return a queue and not a single element?

system-verilog
Prashanth R picture Prashanth R · Nov 16, 2017 · Viewed 9.1k times · Source

I noticed this interesting thing about the max() and min() functions in SV LRM (1800-2012) 7.12 (Array manipulation methods). I tried out the max() and min() functions in a dummy SV file

int a[3] = {0,5,5};
int q[$];
int b;
q = a.max(); // legal
b = a.max(); // illegal

The illegal statement error was

Incompatible complex type assignment
Type of source expression is incompatible with type of target expression.
Mismatching types cannot be used in assignments, initializations and
instantiations. The type of the target is 'int', while the type of the
source is 'int$[$]'.

So I commented out the illegal statement and tested it. It compiled and ran fine but I was hoping to get some more insight as to why the function returns a queue and not a single element - I printed out the contents of q and the size, but the size is still 1 and 5 is being printed just once. Kind of redundant then to make the max() and min() functions return a queue ?

Answer

AndresM picture AndresM · Nov 16, 2017

The "SystemVerilog for Verification" book by Chris Spear and Greg Tumbush has a good explanation on this topic in Chapter 2.6.2, which I am quoting below:

"The array locator methods find data in an unpacked array. At first you may wonder why these return a queue of values. After all, there is only one maximum value in an array. However, SystemVerilog needs a queue for the case when you ask for a value from an empty queue or dynamic array."

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