/*****************************************************************************\
|                        Copyright (C) 2021 Luke Wren                         |
|                     SPDX-License-Identifier: Apache-2.0                     |
\*****************************************************************************/

// Separate ALU for atomic memory operations

`default_nettype none
module hazard3_amo_alu #(
`include "hazard3_config.vh"
,
`include "hazard3_width_const.vh"
) (
	input  wire [W_MEMOP-1:0] op,
	input  wire [W_DATA-1:0]  op_rs1, // From load
	input  wire [W_DATA-1:0]  op_rs2, // From core
	output reg  [W_DATA-1:0]  result
);

`include "hazard3_ops.vh"

wire sub          = op != MEMOP_AMOADD_W;
wire cmp_unsigned = op == MEMOP_AMOMINU_W || op == MEMOP_AMOMAXU_W;

wire [W_DATA-1:0] sum = op_rs1 + (op_rs2 ^ {W_DATA{sub}}) + sub;

wire rs1_lessthan_rs2 =
	op_rs1[W_DATA-1] == op_rs2[W_DATA-1] ? sum[W_DATA-1] :
	cmp_unsigned ?                      op_rs2[W_DATA-1] :
	                                    op_rs1[W_DATA-1] ;

always @ (*) begin
	case(op)
	MEMOP_AMOADD_W:  result = sum;
	MEMOP_AMOXOR_W:  result = op_rs1 ^ op_rs2;
	MEMOP_AMOAND_W:  result = op_rs1 & op_rs2;
	MEMOP_AMOOR_W:   result = op_rs1 | op_rs2;
	MEMOP_AMOMIN_W:  result = rs1_lessthan_rs2 ? op_rs1 : op_rs2;
	MEMOP_AMOMAX_W:  result = rs1_lessthan_rs2 ? op_rs2 : op_rs1;
	MEMOP_AMOMINU_W: result = rs1_lessthan_rs2 ? op_rs1 : op_rs2;
	MEMOP_AMOMAXU_W: result = rs1_lessthan_rs2 ? op_rs2 : op_rs1;
	// AMOSWAP
	default:         result = op_rs2;
	endcase
end

endmodule

`default_nettype wire