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---------------------------------------------------------------------
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-- TITLE: Shifter Unit
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-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
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-- DATE CREATED: 2/2/01
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-- FILENAME: shifter.vhd
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-- PROJECT: M-lite CPU core
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-- COPYRIGHT: Software placed into the public domain by the author.
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-- Software 'as is' without warranty. Author liable for nothing.
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-- DESCRIPTION:
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-- Implements the 32-bit shifter unit.
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---------------------------------------------------------------------
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library ieee;
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use ieee.std_logic_1164.all;
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use work.mlite_pack.all;
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entity shifter is
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port(value : in std_logic_vector(31 downto 0);
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shift_amount : in std_logic_vector(4 downto 0);
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shift_func : in shift_function_type;
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c_shift : out std_logic_vector(31 downto 0));
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end; --entity shifter
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architecture logic of shifter is
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-- type shift_function_type is (
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-- shift_nothing, shift_left_unsigned,
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-- shift_left_signed, shift_right_unsigned);
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begin
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shift_proc: process(value, shift_amount, shift_func) --barrel shifter unit
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variable shift1, shift2, shift4,
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shift8, shift16 : std_logic_vector(31 downto 0);
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variable fills : std_logic_vector(31 downto 16);
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variable go_right : std_logic;
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begin
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if shift_func = shift_right_unsigned or shift_func = shift_right_signed then
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go_right := '1';
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else
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go_right := '0';
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end if;
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if shift_func = shift_right_signed and value(31) = '1' then
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fills := "1111111111111111";
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else
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fills := "0000000000000000";
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end if;
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if go_right = '0' then --shift left
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if shift_amount(0) = '1' then
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shift1 := value(30 downto 0) & '0';
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else
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shift1 := value;
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end if;
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if shift_amount(1) = '1' then
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shift2 := shift1(29 downto 0) & "00";
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else
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shift2 := shift1;
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end if;
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if shift_amount(2) = '1' then
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shift4 := shift2(27 downto 0) & "0000";
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else
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shift4 := shift2;
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end if;
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if shift_amount(3) = '1' then
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shift8 := shift4(23 downto 0) & "00000000";
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else
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shift8 := shift4;
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end if;
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if shift_amount(4) = '1' then
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shift16 := shift8(15 downto 0) & ZERO(15 downto 0);
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else
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shift16 := shift8;
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end if;
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else --shift right
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if shift_amount(0) = '1' then
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shift1 := fills(31) & value(31 downto 1);
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else
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shift1 := value;
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end if;
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if shift_amount(1) = '1' then
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shift2 := fills(31 downto 30) & shift1(31 downto 2);
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else
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shift2 := shift1;
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end if;
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if shift_amount(2) = '1' then
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shift4 := fills(31 downto 28) & shift2(31 downto 4);
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else
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shift4 := shift2;
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end if;
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if shift_amount(3) = '1' then
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shift8 := fills(31 downto 24) & shift4(31 downto 8);
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else
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shift8 := shift4;
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end if;
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if shift_amount(4) = '1' then
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shift16 := fills(31 downto 16) & shift8(31 downto 16);
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else
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shift16 := shift8;
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end if;
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end if; --shift_dir
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if shift_func = shift_nothing then
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c_shift <= ZERO;
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else
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c_shift <= shift16;
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end if;
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end process;
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end; --architecture logic
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