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// =============================================================================

//                           COPYRIGHT NOTICE

// Copyright 2006 (c) Lattice Semiconductor Corporation

// ALL RIGHTS RESERVED

// This confidential and proprietary software may be used only as authorised by

// a licensing agreement from Lattice Semiconductor Corporation.

// The entire notice above must be reproduced on all authorized copies and

// copies may only be made to the extent permitted by a licensing agreement from

// Lattice Semiconductor Corporation.

//

// Lattice Semiconductor Corporation        TEL : 1-800-Lattice (USA and Canada)

// 5555 NE Moore Court                            408-826-6000 (other locations)

// Hillsboro, OR 97124                     web  : http://www.latticesemi.com/

// U.S.A                                   email: techsupport@latticesemi.com

// ============================================================================/

//                         FILE DETAILS

// Project          : LatticeMico32

// File             : lm32_adder.v

// Title            : Integer adder / subtractor with comparison flag generation 

// Dependencies     : lm32_include.v

// Version          : 6.1.17

// =============================================================================

`include "lm32_include.v"

/////////////////////////////////////////////////////

// Module interface

/////////////////////////////////////////////////////

module lm32_adder (

    // ----- Inputs -------

    adder_op_x,

    adder_op_x_n,

    operand_0_x,

    operand_1_x,

    // ----- Outputs -------

    adder_result_x,

    adder_carry_n_x,

    adder_overflow_x

    );

/////////////////////////////////////////////////////

// Inputs

/////////////////////////////////////////////////////

input adder_op_x;                                       // Operating to perform, 0 for addition, 1 for subtraction

input adder_op_x_n;                                     // Inverted version of adder_op_x

input [`LM32_WORD_RNG] operand_0_x;                     // Operand to add, or subtract from

input [`LM32_WORD_RNG] operand_1_x;                     // Opearnd to add, or subtract by

/////////////////////////////////////////////////////

// Outputs

/////////////////////////////////////////////////////

output [`LM32_WORD_RNG] adder_result_x;                 // Result of addition or subtraction

wire   [`LM32_WORD_RNG] adder_result_x;

output adder_carry_n_x;                                 // Inverted carry

wire   adder_carry_n_x;

output adder_overflow_x;                                // Indicates if overflow occured, only valid for subtractions

reg    adder_overflow_x;

/////////////////////////////////////////////////////

// Internal nets and registers 

/////////////////////////////////////////////////////

wire a_sign;                                            // Sign (i.e. positive or negative) of operand 0

wire b_sign;                                            // Sign of operand 1

wire result_sign;                                       // Sign of result

/////////////////////////////////////////////////////

// Instantiations 

/////////////////////////////////////////////////////

lm32_addsub addsub (

    // ----- Inputs -----

    .DataA          (operand_0_x),

    .DataB          (operand_1_x),

    .Cin            (adder_op_x),

    .Add_Sub        (adder_op_x_n),

    // ----- Ouputs -----

    .Result         (adder_result_x),

    .Cout           (adder_carry_n_x)

    );

/////////////////////////////////////////////////////

// Combinational Logic

/////////////////////////////////////////////////////

// Extract signs of operands and result

assign a_sign = operand_0_x[`LM32_WORD_WIDTH-1];

assign b_sign = operand_1_x[`LM32_WORD_WIDTH-1];

assign result_sign = adder_result_x[`LM32_WORD_WIDTH-1];

// Determine whether an overflow occured when performing a subtraction

always @*

begin

    //  +ve - -ve = -ve -> overflow

    //  -ve - +ve = +ve -> overflow

    if  (   (!a_sign & b_sign & result_sign)

         || (a_sign & !b_sign & !result_sign)

        )

        adder_overflow_x = `TRUE;

    else

        adder_overflow_x = `FALSE;

end

endmodule