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75 lines
2.5 KiB
Systemverilog
75 lines
2.5 KiB
Systemverilog
///////////////////////////////////////////
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// shifter.sv
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//
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// Written: David_Harris@hmc.edu 9 January 2021
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// Modified:
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//
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// Purpose: RISC-V 32/64 bit shifter
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//
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// A component of the CORE-V-WALLY configurable RISC-V project.
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//
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// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
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//
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// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
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//
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// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
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// except in compliance with the License, or, at your option, the Apache License version 2.0. You
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// may obtain a copy of the License at
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//
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// https://solderpad.org/licenses/SHL-2.1/
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//
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// Unless required by applicable law or agreed to in writing, any work distributed under the
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// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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////////////////////////////////////////////////////////////////////////////////////////////////
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`include "wally-config.vh"
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module shifter (
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input logic [`XLEN-1:0] A,
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input logic [`LOG_XLEN-1:0] Amt,
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input logic Right, Arith, W64,
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output logic [`XLEN-1:0] Y);
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logic [2*`XLEN-2:0] z, zshift;
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logic [`LOG_XLEN-1:0] amttrunc, offset;
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// Handle left and right shifts with a funnel shifter.
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// For RV32, only 32-bit shifts are needed.
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// For RV64, 32 and 64-bit shifts are needed, with sign extension.
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// funnel shifter input (see CMOS VLSI Design 4e Section 11.8.1, note Table 11.11 shift types wrong)
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if (`XLEN==32) begin:shifter // RV32
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always_comb // funnel mux
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if (Right)
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if (Arith) z = {{31{A[31]}}, A};
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else z = {31'b0, A};
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else z = {A, 31'b0};
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assign amttrunc = Amt; // shift amount
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end else begin:shifter // RV64
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always_comb // funnel mux
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if (W64) begin // 32-bit shifts
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if (Right)
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if (Arith) z = {64'b0, {31{A[31]}}, A[31:0]};
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else z = {95'b0, A[31:0]};
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else z = {32'b0, A[31:0], 63'b0};
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end else begin
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if (Right)
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if (Arith) z = {{63{A[63]}}, A};
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else z = {63'b0, A};
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else z = {A, 63'b0};
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end
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assign amttrunc = W64 ? {1'b0, Amt[4:0]} : Amt; // 32 or 64-bit shift
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end
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// opposite offset for right shfits
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assign offset = Right ? amttrunc : ~amttrunc;
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// funnel operation
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assign zshift = z >> offset;
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assign Y = zshift[`XLEN-1:0];
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endmodule
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