RE: [sv-bc] Function cannot return Unpack Array but can return unpack typedef

The quick answer is that the BNF only allows a basic data type to be
specified in this spot, and an unpacked array is not a basic data type.
I would have liked it to have been even stricter, like only allow
simple_types since it makes no sense to declare an anonymous struct as
the return type of a function.

 

The original reason for disallowing this goes back to SUPERLOG, which
had pointers to functions and there was ambiguity in whether your intent
was an array of function pointers or an unpacked array return type This
was further complicated because of the existence of packed and unpacked
array dimensions. 

 

________________________________

From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
Abhishek Roy
Sent: Tuesday, July 05, 2005 12:27 AM
To: sv-bc
Cc: Antara Ghosh; Saikat Bandyopadhyay
Subject: [sv-bc] Function cannot return Unpack Array but can return
unpack typedef

 

Hi all,

Consider the following scenario :-

/***********************************************************************
**************/
module test (input [7:0] in1, output bit [3:0] out1 [1:0]);

function  bit [3:0] func_arr [1:0] (bit [7:0] arg);  //invalid syntax :
function cannot return unpack array
begin
    func_arr[1] = arg[7:4];
    func_arr[0] = arg[3:0];
end
endfunction

typedef bit [3:0] bit_arr [1:0];
function  bit_arr func_type (bit [7:0] arg); //valid syntax : But
bit_arr is still unpack typedef
begin
    func_type[1] = arg[7:4];
    func_type[0] = arg[3:0];
end
endfunction

always@(*)
begin
    out1 = func_arr(in1); //invalid assignment
    out1 = func_type(in1); //valid assignment
end

endmodule
/***********************************************************************
**************/

Hence, when  a function can return object of unpack typedef , then why
not unpack array.

regards
-Abhishek Roy


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