How to write a part select expression using shift operator in system verilog?

Question

How to write a part select expression using shift operator in system Verilog?
Given a memory word

logic [0:8] memword;

How to write the part select expression memword[i:j] in shift operator? If not shift operator, can you please suggest other expressions?

i and j can be any indexing expression. We will assign this memory word to another memory word with |i-j| width.

Consider both left to right and right to left indexing.

use case: writing an alternative statement for the part select for compiler related optimization

The memory could be used anywhere in the program

always @(posedge clk) begin
   if (memword[i:j]) begin
      mem2 = memword[i:j];
   end
end

The main usage is to eliminate part select.

dave_59 · Accepted Answer · 2025-02-27 20:06:19Z

1

For the code shown, you could write a function to mask the part select, and shift it into the lsb.

logic [8:0] memword;


class vector#(int WIDTH);
    typedef logic [WIDTH-1:0] w_t;
    
    static function w_t slice(w_t vector, int L,R);
      int slice_width = L-R+1;
      w_t mask = (1'b1 << slice_width) -1;
      return vector >> R  & mask;
    endfunction
  endclass

always @(posedge clk) begin
   if (vector#(9)::slice(memword,i,j) begin
      mem2 = vector#(9)::slice(memword,i,j)
   end
end

Although you could write this function to deal with both big and little endian indexing, It might be easier to write two seperate functions.

answered Feb 27 at 20:06

dave_59

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