| 1 |
2 |
rhoads |
---------------------------------------------------------------------
|
| 2 |
|
|
-- TITLE: Shifter Unit
|
| 3 |
|
|
-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
|
| 4 |
|
|
-- DATE CREATED: 2/2/01
|
| 5 |
|
|
-- FILENAME: shifter.vhd
|
| 6 |
43 |
rhoads |
-- PROJECT: Plasma CPU core
|
| 7 |
2 |
rhoads |
-- COPYRIGHT: Software placed into the public domain by the author.
|
| 8 |
|
|
-- Software 'as is' without warranty. Author liable for nothing.
|
| 9 |
|
|
-- DESCRIPTION:
|
| 10 |
|
|
-- Implements the 32-bit shifter unit.
|
| 11 |
|
|
---------------------------------------------------------------------
|
| 12 |
|
|
library ieee;
|
| 13 |
|
|
use ieee.std_logic_1164.all;
|
| 14 |
39 |
rhoads |
use work.mlite_pack.all;
|
| 15 |
2 |
rhoads |
|
| 16 |
|
|
entity shifter is
|
| 17 |
|
|
port(value : in std_logic_vector(31 downto 0);
|
| 18 |
|
|
shift_amount : in std_logic_vector(4 downto 0);
|
| 19 |
|
|
shift_func : in shift_function_type;
|
| 20 |
|
|
c_shift : out std_logic_vector(31 downto 0));
|
| 21 |
|
|
end; --entity shifter
|
| 22 |
|
|
|
| 23 |
|
|
architecture logic of shifter is
|
| 24 |
|
|
-- type shift_function_type is (
|
| 25 |
|
|
-- shift_nothing, shift_left_unsigned,
|
| 26 |
|
|
-- shift_left_signed, shift_right_unsigned);
|
| 27 |
|
|
begin
|
| 28 |
|
|
|
| 29 |
|
|
shift_proc: process(value, shift_amount, shift_func) --barrel shifter unit
|
| 30 |
|
|
variable shift1, shift2, shift4,
|
| 31 |
|
|
shift8, shift16 : std_logic_vector(31 downto 0);
|
| 32 |
|
|
variable fills : std_logic_vector(31 downto 16);
|
| 33 |
|
|
variable go_right : std_logic;
|
| 34 |
|
|
begin
|
| 35 |
|
|
if shift_func = shift_right_unsigned or shift_func = shift_right_signed then
|
| 36 |
|
|
go_right := '1';
|
| 37 |
|
|
else
|
| 38 |
|
|
go_right := '0';
|
| 39 |
|
|
end if;
|
| 40 |
|
|
if shift_func = shift_right_signed and value(31) = '1' then
|
| 41 |
|
|
fills := "1111111111111111";
|
| 42 |
|
|
else
|
| 43 |
|
|
fills := "0000000000000000";
|
| 44 |
|
|
end if;
|
| 45 |
|
|
if go_right = '0' then --shift left
|
| 46 |
|
|
if shift_amount(0) = '1' then
|
| 47 |
|
|
shift1 := value(30 downto 0) & '0';
|
| 48 |
|
|
else
|
| 49 |
|
|
shift1 := value;
|
| 50 |
|
|
end if;
|
| 51 |
|
|
if shift_amount(1) = '1' then
|
| 52 |
|
|
shift2 := shift1(29 downto 0) & "00";
|
| 53 |
|
|
else
|
| 54 |
|
|
shift2 := shift1;
|
| 55 |
|
|
end if;
|
| 56 |
|
|
if shift_amount(2) = '1' then
|
| 57 |
|
|
shift4 := shift2(27 downto 0) & "0000";
|
| 58 |
|
|
else
|
| 59 |
|
|
shift4 := shift2;
|
| 60 |
|
|
end if;
|
| 61 |
|
|
if shift_amount(3) = '1' then
|
| 62 |
|
|
shift8 := shift4(23 downto 0) & "00000000";
|
| 63 |
|
|
else
|
| 64 |
|
|
shift8 := shift4;
|
| 65 |
|
|
end if;
|
| 66 |
|
|
if shift_amount(4) = '1' then
|
| 67 |
|
|
shift16 := shift8(15 downto 0) & ZERO(15 downto 0);
|
| 68 |
|
|
else
|
| 69 |
|
|
shift16 := shift8;
|
| 70 |
|
|
end if;
|
| 71 |
|
|
else --shift right
|
| 72 |
|
|
if shift_amount(0) = '1' then
|
| 73 |
|
|
shift1 := fills(31) & value(31 downto 1);
|
| 74 |
|
|
else
|
| 75 |
|
|
shift1 := value;
|
| 76 |
|
|
end if;
|
| 77 |
|
|
if shift_amount(1) = '1' then
|
| 78 |
|
|
shift2 := fills(31 downto 30) & shift1(31 downto 2);
|
| 79 |
|
|
else
|
| 80 |
|
|
shift2 := shift1;
|
| 81 |
|
|
end if;
|
| 82 |
|
|
if shift_amount(2) = '1' then
|
| 83 |
|
|
shift4 := fills(31 downto 28) & shift2(31 downto 4);
|
| 84 |
|
|
else
|
| 85 |
|
|
shift4 := shift2;
|
| 86 |
|
|
end if;
|
| 87 |
|
|
if shift_amount(3) = '1' then
|
| 88 |
|
|
shift8 := fills(31 downto 24) & shift4(31 downto 8);
|
| 89 |
|
|
else
|
| 90 |
|
|
shift8 := shift4;
|
| 91 |
|
|
end if;
|
| 92 |
|
|
if shift_amount(4) = '1' then
|
| 93 |
|
|
shift16 := fills(31 downto 16) & shift8(31 downto 16);
|
| 94 |
|
|
else
|
| 95 |
|
|
shift16 := shift8;
|
| 96 |
|
|
end if;
|
| 97 |
|
|
end if; --shift_dir
|
| 98 |
|
|
if shift_func = shift_nothing then
|
| 99 |
|
|
c_shift <= ZERO;
|
| 100 |
|
|
else
|
| 101 |
|
|
c_shift <= shift16;
|
| 102 |
|
|
end if;
|
| 103 |
|
|
end process;
|
| 104 |
|
|
|
| 105 |
|
|
end; --architecture logic
|
| 106 |
|
|
|
