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[/] [plasma/] [tags/] [Version_1_0/] [vhdl/] [shifter.vhd] - Rev 5
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--------------------------------------------------------------------- -- TITLE: Shifter Unit -- AUTHOR: Steve Rhoads (rhoadss@yahoo.com) -- DATE CREATED: 2/2/01 -- FILENAME: shifter.vhd -- PROJECT: MIPS 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.mips_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 shift1, shift2, shift4, shift8, shift16 : 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 shift1 := value(30 downto 0) & '0'; else shift1 := value; end if; if shift_amount(1) = '1' then shift2 := shift1(29 downto 0) & "00"; else shift2 := shift1; end if; if shift_amount(2) = '1' then shift4 := shift2(27 downto 0) & "0000"; else shift4 := shift2; end if; if shift_amount(3) = '1' then shift8 := shift4(23 downto 0) & "00000000"; else shift8 := shift4; end if; if shift_amount(4) = '1' then shift16 := shift8(15 downto 0) & ZERO(15 downto 0); else shift16 := shift8; end if; else --shift right if shift_amount(0) = '1' then shift1 := fills(31) & value(31 downto 1); else shift1 := value; end if; if shift_amount(1) = '1' then shift2 := fills(31 downto 30) & shift1(31 downto 2); else shift2 := shift1; end if; if shift_amount(2) = '1' then shift4 := fills(31 downto 28) & shift2(31 downto 4); else shift4 := shift2; end if; if shift_amount(3) = '1' then shift8 := fills(31 downto 24) & shift4(31 downto 8); else shift8 := shift4; end if; if shift_amount(4) = '1' then shift16 := fills(31 downto 16) & shift8(31 downto 16); else shift16 := shift8; end if; end if; --shift_dir if shift_func = shift_nothing then -- c_shift <= "ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ"; c_shift <= ZERO; else c_shift <= shift16; end if; end process; end; --architecture logic
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