///////////////////////////////////////////
// csa.sv
//
// Written: Katherine Parry and David_Harris@hmc.edu 21 August 2022
// Modified: 
//
// Purpose: 3:2 carry-save adder
// 
// A component of the CORE-V-WALLY configurable RISC-V project.
// 
// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
//
// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
//
// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file 
// except in compliance with the License, or, at your option, the Apache License version 2.0. You 
// may obtain a copy of the License at
//
// https://solderpad.org/licenses/SHL-2.1/
//
// Unless required by applicable law or agreed to in writing, any work distributed under the 
// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, 
// either express or implied. See the License for the specific language governing permissions 
// and limitations under the License.
////////////////////////////////////////////////////////////////////////////////////////////////

module csa #(parameter N=16) (
  input  logic [N-1:0] x, y, z, 
  input  logic         cin, 
  output logic [N-1:0] s, c
);

  // This block adds x, y, z, and cin to produce 
  // a result s / c in carry-save redundant form.
  // cin is just added to the least significant bit
  // s + c = x + y + z + cin
 
  assign s = x ^ y ^ z;
  assign c = {x[N-2:0] & (y[N-2:0] | z[N-2:0]) | (y[N-2:0] & z[N-2:0]), cin};
endmodule