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---------------------------------------------------------------------
-- TITLE: Shifter Unit
-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
-- DATE CREATED: 2/2/01
-- FILENAME: shifter.vhd
-- PROJECT: Plasma CPU core
-- COPYRIGHT: Software placed into the public domain by the author.
--    Software 'as is' without warranty.  Author liable for nothing.
-- DESCRIPTION:
--    Implements the 32-bit shifter unit.
---------------------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;
use work.mlite_pack.all;
 
entity shifter is
   port(value        : in  std_logic_vector(31 downto 0);
        shift_amount : in  std_logic_vector(4 downto 0);
        shift_func   : in  shift_function_type;
        c_shift      : out std_logic_vector(31 downto 0));
end; --entity shifter
 
architecture logic of shifter is
--   type shift_function_type is (
--      shift_nothing, shift_left_unsigned, 
--      shift_left_signed, shift_right_unsigned);
begin
 
shift_proc: process(value, shift_amount, shift_func)  --barrel shifter unit
   variable shift1L, shift2L, shift4L, shift8L, shift16 :
      std_logic_vector(31 downto 0);
   variable shift1R, shift2R, shift4R, shift8R :
      std_logic_vector(31 downto 0);
   variable fills : std_logic_vector(31 downto 16);
variable go_right : std_logic;
begin
   if shift_func = shift_right_unsigned or shift_func = shift_right_signed then
      go_right := '1';
   else
      go_right := '0';
   end if;
   if shift_func = shift_right_signed and value(31) = '1' then
      fills := "1111111111111111";
   else
      fills := "0000000000000000";
   end if;
   if go_right = '0' then  --shift left
      if shift_amount(0) = '1' then
         shift1L := value(30 downto 0) & '0';
      else
         shift1L := value;
      end if;
      if shift_amount(1) = '1' then
         shift2L := shift1L(29 downto 0) & "00";
      else
         shift2L := shift1L;
      end if;
      if shift_amount(2) = '1' then
         shift4L := shift2L(27 downto 0) & "0000";
      else
         shift4L := shift2L;
      end if;
      if shift_amount(3) = '1' then
         shift8L := shift4L(23 downto 0) & "00000000";
      else
         shift8L := shift4L;
      end if;
      if shift_amount(4) = '1' then
         shift16 := shift8L(15 downto 0) & ZERO(15 downto 0);
      else
         shift16 := shift8L;
      end if;
   else  --shift right
      if shift_amount(0) = '1' then
         shift1R := fills(31) & value(31 downto 1);
      else
         shift1R := value;
      end if;
      if shift_amount(1) = '1' then
         shift2R := fills(31 downto 30) & shift1R(31 downto 2);
      else
         shift2R := shift1R;
      end if;
      if shift_amount(2) = '1' then
         shift4R := fills(31 downto 28) & shift2R(31 downto 4);
      else
         shift4R := shift2R;
      end if;
      if shift_amount(3) = '1' then
         shift8R := fills(31 downto 24) & shift4R(31 downto 8);
      else
         shift8R := shift4R;
      end if;
      if shift_amount(4) = '1' then
         shift16 := fills(31 downto 16) & shift8R(31 downto 16);
      else
         shift16 := shift8R;
      end if;
   end if;  --shift_dir
   if shift_func = shift_nothing then
      c_shift <= ZERO;
   else
      c_shift <= shift16;
   end if;
end process;
 
end; --architecture logic
 

Line No.	Rev	Author	Line
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	87	rhoads	`variable shift1L, shift2L, shift4L, shift8L, shift16 :`
31			`std_logic_vector(31 downto 0);`
32			`variable shift1R, shift2R, shift4R, shift8R :`
33			`std_logic_vector(31 downto 0);`
34	2	rhoads	`variable fills : std_logic_vector(31 downto 16);`
35			`variable go_right : std_logic;`
36			`begin`
37			`if shift_func = shift_right_unsigned or shift_func = shift_right_signed then`
38			`go_right := '1';`
39			`else`
40			`go_right := '0';`
41			`end if;`
42			`if shift_func = shift_right_signed and value(31) = '1' then`
43			`fills := "1111111111111111";`
44			`else`
45			`fills := "0000000000000000";`
46			`end if;`
47			`if go_right = '0' then --shift left`
48			`if shift_amount(0) = '1' then`
49	87	rhoads	`shift1L := value(30 downto 0) & '0';`
50	2	rhoads	`else`
51	87	rhoads	`shift1L := value;`
52	2	rhoads	`end if;`
53			`if shift_amount(1) = '1' then`
54	87	rhoads	`shift2L := shift1L(29 downto 0) & "00";`
55	2	rhoads	`else`
56	87	rhoads	`shift2L := shift1L;`
57	2	rhoads	`end if;`
58			`if shift_amount(2) = '1' then`
59	87	rhoads	`shift4L := shift2L(27 downto 0) & "0000";`
60	2	rhoads	`else`
61	87	rhoads	`shift4L := shift2L;`
62	2	rhoads	`end if;`
63			`if shift_amount(3) = '1' then`
64	87	rhoads	`shift8L := shift4L(23 downto 0) & "00000000";`
65	2	rhoads	`else`
66	87	rhoads	`shift8L := shift4L;`
67	2	rhoads	`end if;`
68			`if shift_amount(4) = '1' then`
69	87	rhoads	`shift16 := shift8L(15 downto 0) & ZERO(15 downto 0);`
70	2	rhoads	`else`
71	87	rhoads	`shift16 := shift8L;`
72	2	rhoads	`end if;`
73			`else --shift right`
74			`if shift_amount(0) = '1' then`
75	87	rhoads	`shift1R := fills(31) & value(31 downto 1);`
76	2	rhoads	`else`
77	87	rhoads	`shift1R := value;`
78	2	rhoads	`end if;`
79			`if shift_amount(1) = '1' then`
80	87	rhoads	`shift2R := fills(31 downto 30) & shift1R(31 downto 2);`
81	2	rhoads	`else`
82	87	rhoads	`shift2R := shift1R;`
83	2	rhoads	`end if;`
84			`if shift_amount(2) = '1' then`
85	87	rhoads	`shift4R := fills(31 downto 28) & shift2R(31 downto 4);`
86	2	rhoads	`else`
87	87	rhoads	`shift4R := shift2R;`
88	2	rhoads	`end if;`
89			`if shift_amount(3) = '1' then`
90	87	rhoads	`shift8R := fills(31 downto 24) & shift4R(31 downto 8);`
91	2	rhoads	`else`
92	87	rhoads	`shift8R := shift4R;`
93	2	rhoads	`end if;`
94			`if shift_amount(4) = '1' then`
95	87	rhoads	`shift16 := fills(31 downto 16) & shift8R(31 downto 16);`
96	2	rhoads	`else`
97	87	rhoads	`shift16 := shift8R;`
98	2	rhoads	`end if;`
99			`end if; --shift_dir`
100			`if shift_func = shift_nothing then`
101			`c_shift <= ZERO;`
102			`else`
103			`c_shift <= shift16;`
104			`end if;`
105			`end process;`
106
107			`end; --architecture logic`
108

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[/] [mlite/] [tags/] [V3_0/] [vhdl/] [shifter.vhd] - Blame information for rev 87