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`timescale 1ns / 1ps
// ============================================================================
//        __
//   \\__/ o\    (C) 2016-2018  Robert Finch, Waterloo
//    \  __ /    All rights reserved.
//     \/_//     robfinch<remove>@finitron.ca
//       ||
//
//	FT64_bitfield.v
//		
//
// This source file is free software: you can redistribute it and/or modify 
// it under the terms of the GNU Lesser General Public License as published 
// by the Free Software Foundation, either version 3 of the License, or     
// (at your option) any later version.                                      
//                                                                          
// This source file is distributed in the hope that it will be useful,      
// but WITHOUT ANY WARRANTY; without even the implied warranty of           
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the            
// GNU General Public License for more details.                             
//                                                                          
// You should have received a copy of the GNU General Public License        
// along with this program.  If not, see <http://www.gnu.org/licenses/>.    
//                                                                          
//
// ============================================================================
//
`ifndef BFSET
`define BFSET     4'd0
`define BFCLR     4'd1
`define BFCHG     4'd2 
`define BFINS     4'd3
`define BFINSI    4'd4
`define BFEXT     4'd5
`define BFEXTU    4'd6
`endif
 
module FT64_bitfield(inst, a, b, o, masko);
parameter DWIDTH=64;
input [31:0] inst;
input [DWIDTH-1:0] a;
input [DWIDTH-1:0] b;
output [DWIDTH-1:0] o;
reg [DWIDTH-1:0] o;
output [DWIDTH-1:0] masko;
 
reg [DWIDTH-1:0] o1;
reg [DWIDTH-1:0] o2;
 
// generate mask
reg [DWIDTH-1:0] mask;
assign masko = mask;
wire [3:0] op = inst[31:28];
wire [5:0] mb = inst[21:16];
wire [5:0] me = inst[27:22];
wire [5:0] ml = me-mb;		// mask length-1
wire [63:0] imm = {59'd0,inst[10:6]};
 
integer nn,n;
always @(mb or me or nn)
	for (nn = 0; nn < DWIDTH; nn = nn + 1)
		mask[nn] <= (nn >= mb) ^ (nn <= me) ^ (me >= mb);
 
always @(op,mask,b,a,imm,mb,ml)
case (op)
`BFINS: 	begin
				o2 = a << mb;
				for (n = 0; n < DWIDTH; n = n + 1) o[n] = (mask[n] ? o2[n] : b[n]);
			end
`BFINSI: 	begin
				o2 = imm << mb;
				for (n = 0; n < DWIDTH; n = n + 1) o[n] = (mask[n] ? o2[n] : b[n]);
			end
`BFSET: 	begin for (n = 0; n < DWIDTH; n = n + 1) o[n] = mask[n] ? 1'b1 : a[n]; end
//`BFCLR: 	begin for (n = 0; n < DWIDTH; n = n + 1) o[n] = mask[n] ? 1'b0 : a[n]; end
`BFCHG: 	begin for (n = 0; n < DWIDTH; n = n + 1) o[n] = mask[n] ? ~a[n] : a[n]; end
`BFEXTU:	begin
				for (n = 0; n < DWIDTH; n = n + 1)
					o1[n] = mask[n] ? a[n] : 1'b0;
				o = o1 >> mb;
			end
`BFEXT:		begin
				for (n = 0; n < DWIDTH; n = n + 1)
					o1[n] = mask[n] ? a[n] : 1'b0;
				o2 = o1 >> mb;
				for (n = 0; n < DWIDTH; n = n + 1)
					o[n] = n > ml ? o2[ml] : o2[n];
			end
`ifdef I_SEXT
`SEXT:		begin for (n = 0; n < DWIDTH; n = n + 1) o[n] = mask[n] ? a[mb] : a[n]; end
`endif
default:	o = {DWIDTH{1'b0}};
endcase
 
endmodule