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--
-- FFS - Find first (least-significant) set bit
--
-- Custom instruction for Nios II
--
-- Copyright (C) 2012 Tobias Klauser <tklauser@distanz.ch>
--
-- This source file may be used and distributed without
-- restriction provided that this copyright statement is not
-- removed from the file and that any derivative work contains
-- the original copyright notice and the associated disclaimer.
--
-- This source file is free software; you can redistribute it
-- and/or modify it under the terms of the GNU Lesser General
-- Public License as published by the Free Software Foundation;
-- either version 2.1 of the License, or (at your option) any
-- later version.
--
-- This source is distributed in the hope that it will be
-- useful, but WITHOUT ANY WARRANTY; without even the implied
-- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
-- PURPOSE. See the GNU Lesser General Public License for more
-- details.
--
-- You should have received a copy of the GNU Lesser General
-- Public License along with this source; if not, download it
-- from http://www.opencores.org/lgpl.shtml
--
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.numeric_std.all;
entity ffs is
port(
signal dataa : in std_logic_vector(31 downto 0);
signal result : out std_logic_vector(31 downto 0)
);
end entity ffs;
architecture rtl of ffs is
begin
process(dataa)
variable word : unsigned(result'range);
variable ret : unsigned(result'range);
begin
ret := to_unsigned(0, ret'length);
for i in dataa'range loop
if dataa(i) = '1' then
ret := to_unsigned(i + 1, ret'length);
end if;
end loop;
result <= std_logic_vector(ret);
end process;
end architecture rtl;
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