1 | function shift_f
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2 | (a : in std_logic_vector(31 downto 0);
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3 | b : in std_logic_vector(31 downto 0);
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4 | shift_func : in shift_function_type;
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5 | rt_data : in std_logic_vector(31 downto 0))
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6 | return std_logic_vector
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7 |
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8 | is
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9 |
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10 | --barrel shifter unit
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11 | variable shift1L, shift2L, shift4L, shift8L, shift16 :
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12 | std_logic_vector(31 downto 0);
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13 | variable shift1R, shift2R, shift4R, shift8R :
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14 | std_logic_vector(31 downto 0);
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15 | variable fills : std_logic_vector(31 downto 16);
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16 | variable shiftnumber : std_logic_vector(4 downto 0);
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17 | begin
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18 |
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19 | if (shift_func(1) = '1' and rt_data(31) = '1') then
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20 | fills := "1111111111111111";
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21 | else
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22 | fills := "0000000000000000";
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23 | end if;
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24 |
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25 | if shift_func(2) = '0' then
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26 | shiftnumber := b(10 downto 6);
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27 | else
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28 | shiftnumber := a(4 downto 0);
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29 | end if;
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30 | --SLL rd<_rt << sa
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31 | if shift_func (0) = '0' then -- shift left
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32 | if shiftnumber(0) = '1' then
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33 | shift1L := rt_data(30 downto 0) & '0';
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34 | else
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35 | shift1L := rt_data;
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36 | end if;
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37 | if shiftnumber(1) = '1' then
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38 | shift2L := shift1L(29 downto 0) & "00";
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39 | else
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40 | shift2L := shift1L;
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41 | end if;
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42 | if shiftnumber(2) = '1' then
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43 | shift4L := shift2L(27 downto 0) & "0000";
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44 | else
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45 | shift4L := shift2L;
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46 | end if;
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47 | if shiftnumber(3) = '1' then
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48 | shift8L := shift4L(23 downto 0) & "00000000";
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49 | else
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50 | shift8L := shift4L;
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51 | end if;
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52 | if shiftnumber(4) = '1' then
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53 | shift16 := shift8L(15 downto 0) & X"0000";
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54 | else
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55 | shift16 := shift8L;
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56 | end if;
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57 |
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58 | else --shift right
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59 | if shiftnumber(0) = '1' then
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60 | shift1R := fills(31) & rt_data(31 downto 1);
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61 | else
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62 | shift1R := rt_data;
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63 | end if;
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64 | if shiftnumber(1) = '1' then
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65 | shift2R := fills(31 downto 30) & shift1R(31 downto 2);
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66 | else
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67 | shift2R := shift1R;
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68 | end if;
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69 | if shiftnumber(2) = '1' then
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70 | shift4R := fills(31 downto 28) & shift2R(31 downto 4);
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71 | else
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72 | shift4R := shift2R;
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73 | end if;
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74 | if shiftnumber(3) = '1' then
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75 | shift8R := fills(31 downto 24) & shift4R(31 downto 8);
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76 | else
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77 | shift8R := shift4R;
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78 | end if;
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79 | if shiftnumber(4) = '1' then
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80 | shift16 := fills(31 downto 16) & shift8R(31 downto 16);
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81 | else
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82 | shift16 := shift8R;
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83 | end if;
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84 | end if;
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85 | return(shift16);
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86 |
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87 | end shift_f;
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