arith_utils.vhd

来自「VHDL的基本数学运算库,非常好用」· VHDL 代码 · 共 66 行

-------------------------------------------------------------------------------
-- Title       : Utility functions
-- Project     : VHDL Library of Arithmetic Units
-------------------------------------------------------------------------------
-- File        : arith_utils.vhd
-- Author      : Reto Zimmermann  <[e-mail]>
-- Company     : Integrated Systems Laboratory, ETH Zurich
-- Date        : 1997/11/04
-------------------------------------------------------------------------------
-- Copyright (c) 1998 Integrated Systems Laboratory, ETH Zurich
-------------------------------------------------------------------------------
-- Description :
-- Package of utility functions used in code for arithmetic units.
-------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;

-------------------------------------------------------------------------------

package arith_utils is
  
  function log2ceil (n : integer) return integer;

  function log2floor (n : integer) return integer;

end arith_utils;

-------------------------------------------------------------------------------

package body arith_utils is

  -- purpose: computes ceil(log2(n))
  function log2ceil (n : integer) return integer is
    variable m, p : integer;
  begin
    m := 0;
    p := 1;
    for i in 0 to n loop
      if p < n then
        m := m + 1;
        p := p * 2;
      end if;
    end loop;
    return m;
  end log2ceil;    

  -- purpose: computes floor(log2(n))
  function log2floor (n : integer) return integer is
    variable m, p : integer;
  begin
    m := -1;
    p := 1;
    for i in 0 to n loop
      if p <= n then
        m := m + 1;
        p := p * 2;
      end if;
    end loop;
    return m;
  end log2floor;    

end arith_utils;

-------------------------------------------------------------------------------