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tomburkeii |
`timescale 1ns / 1ps
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//////////////////////////////////////////////////////////////////////////////////
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// Company:
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// Engineer:
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//
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// Create Date: 09:28:18 08/24/2011
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// Design Name:
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// Module Name: q15_add
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// Project Name:
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// Target Devices:
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// Tool versions:
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// Description:
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//
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// Dependencies:
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//
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// Revision:
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// Revision 0.01 - File Created
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// Additional Comments:
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//
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//////////////////////////////////////////////////////////////////////////////////
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module qadd #(
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//Parameterized values
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parameter Q = 15,
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parameter N = 32
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)
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(
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input [N-1:0] a,
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input [N-1:0] b,
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output [N-1:0] c
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);
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reg [N-1:0] res;
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assign c = res;
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always @(a,b) begin
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// both negative or both positive
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if(a[N-1] == b[N-1]) begin // Since they have the same sign, absolute magnitude increases
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res[N-2:0] = a[N-2:0] + b[N-2:0]; // So we just add the two numbers
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res[N-1] = a[N-1]; // and set the sign appropriately... Doesn't matter which one we use,
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// they both have the same sign
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// Do the sign last, on the off-chance there was an overflow...
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end // Not doing any error checking on this...
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// one of them is negative...
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else if(a[N-1] == 0 && b[N-1] == 1) begin // subtract a-b
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if( a[N-2:0] > b[N-2:0] ) begin // if a is greater than b,
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res[N-2:0] = a[N-2:0] - b[N-2:0]; // then just subtract b from a
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res[N-1] = 0; // and manually set the sign to positive
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end
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else begin // if a is less than b,
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res[N-2:0] = b[N-2:0] - a[N-2:0]; // we'll actually subtract a from b to avoid a 2's complement answer
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if (res[N-2:0] == 0)
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res[N-1] = 0; // I don't like negative zero....
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else
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res[N-1] = 1; // and manually set the sign to negative
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end
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end
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else begin // subtract b-a (a negative, b positive)
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if( a[N-2:0] > b[N-2:0] ) begin // if a is greater than b,
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res[N-2:0] = a[N-2:0] - b[N-2:0]; // we'll actually subtract b from a to avoid a 2's complement answer
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if (res[N-2:0] == 0)
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res[N-1] = 0; // I don't like negative zero....
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else
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res[N-1] = 1; // and manually set the sign to negative
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end
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else begin // if a is less than b,
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res[N-2:0] = b[N-2:0] - a[N-2:0]; // then just subtract a from b
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res[N-1] = 0; // and manually set the sign to positive
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end
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end
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end
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endmodule
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