HBLbits_Verilog Basic_shift18

 HBLbits_Verilog Basic_shift18

Build a 64-bit arithmetic shift register, with synchronous load. The shifter can shift both left and right, and by 1 or 8 bit positions, selected by amount.

An arithmetic right shift shifts in the sign bit of the number in the shift register (q[63] in this case) instead of zero as done by a logical right shift. Another way of thinking about an arithmetic right shift is that it assumes the number being shifted is signed and preserves the sign, so that arithmetic right shift divides a signed number by a power of two.

There is no difference between logical and arithmetic left shifts.

• load: Loads shift register with data[63:0] instead of shifting.
• ena: Chooses whether to shift.
• amount: Chooses which direction and how much to shift.
  • 2'b00: shift left by 1 bit.
  • 2'b01: shift left by 8 bits.
  • 2'b10: shift right by 1 bit.
  • 2'b11: shift right by 8 bits.
• q: The contents of the shifter.

A left arithmetic shift of a binary number by 1. The empty position in the least significant bit is filled with a zero.

A right arithmetic shift of a binary number by 1. The empty position in the most significant bit is filled with a copy of the original MSB.

module top_module(

    input clk,
    input load,
    input ena,
    input [1:0] amount,
    input [63:0] data,
    output reg [63:0] q); 
    
    always @(posedge clk) begin
        if(load)
            q <= data;
        else if (ena)
            begin
                case(amount)
                    2'b00: q <= {q[62:0],1'b0};
                    2'b01: q <= {q[55:0],8'b0};
                    2'b10: q <= {q[63],q[63:1]};
                    2'b11: q <= {{8{q[63]}},q[63-:56]};
                endcase
                
            end
        
    end
endmodule