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上传时间: 2013-04-26
详细说明： 32位桶氏移位器，实现了逻辑左移、逻辑右移和算术右移，以下是代码片段： -- bshift.vhdl A barrel shifter for 32 bit words -- includes shift left logical (sll), shift right logical(srl) and -- shift right arithmetic (sra) -- both behavioral and circuit models (two architectures) included -- -- Note: behavior requires util_package for 'to_integer' -- circuit requires mux_32 component -- the physical circuit uses 17 mux's, 7 mux delay library IEEE; use IEEE.std_logic_11 64.all; Entity bshift is -- barrel shifter port (left : in std_logic; -- '1' for left, '0' for right logical : in std_logic; -- '1' for logical, '0' for arithmetic shift : in std_logic_vector(4 downto 0); -- shift count input : in std_logic_vector (31 downto 0); output : out std_logic_vector (31 downto 0) ); end entity bshift; architecture behavior of bshift is function to_integer(sig : std_logic_vector) return integer is variable num : integer := 0; -- descending sig as integer begin for i in sig'range loop if sig(i)='1' then num := num*2+1; else num := num*2; end if; end loop; -- i return num; end function to_integer; begin -- behavior shft32: process(left, logical, input, shift) variable shft : integer; variable out_right_arithmetic : std_logic_vector(31 downto 0); variable out_right_logical : std_logic_vector(31 downto 0); variable out_left_logical : std_logic_vector(31 downto 0); begin shft := to_integer(shift); if logical = '0' then out_right_arithmetic := (31 downto 32-shft => input(31)) & input(31 downto shft); output <= out_right_arithmetic after 250 ps; else if left = '1' then out_left_logical := input(31-shft downto 0) & (shft-1 downto 0 => '0'); output <= out_left_logical after 250 ps; else out_right_logical := (31 downto 32-shft => '0') & input(31 downto shft); output <= out_right_logical after 250 ps; end if; end if; end process shft32; end architecture behavior; -- of bshift ...展开收缩
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