VHDL的库

STD_LOGIC_ARITH

扩展了UNSIGNED、SIGNED、SMALL_INT(短整型)三个数据类型，并定义了相关的算术运算和转换函数。

--================================================

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;

entity mux1 is
port(
  sclk : in std_logic;
  rst_n: in std_logic;
  count: buffer std_logic_vector(4 downto 0)
 );
end mux1;

architecture ok of mux1 is
signal cnt : std_logic_vector(4 downto 0);
begin
 
 process
 begin
  wait until sclk'event and sclk= '1';
   if rst_n = '0' then
    cnt <=(others =>'0');
   elsif unsigned(cnt ) >= 10 then
    cnt <= (others =>'0');
   else
    cnt <= unsigned(cnt) + 2;
   end if;
   
 end process;
count <= cnt;
end ok;

--========================================================

use IEEE.NUMERIC_STD.

支持整数的MOD，REM，ABS　　等运算

    dd <= 5 mod 3;
    dd <= 5 rem 3;
    dd <= abs(-3);