逻辑单元使用过多怎么瘦身

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;

ENtiTY TAX2 IS
GENERIC(R1:INTEGER:=3;R2:INTEGER:=4;R3:INTEGER:=5;R4:INTEGER:=6);
PORT(CLK,K4,K5:IN STD_LOGIC;
     S0,S1:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
     W:IN STD_LOGIC_VECTOR(4 DOWNTO 0);
     Y3,Y2,Y1,Y0:OUT STD_LOGIC_VECTOR(3 DOWNTO 0)
     );
END;

ARCHITECTURE ONE OF TAX2 IS
  SIGNAL LC,DD_RATE,LC_RATE,RATE,BAI,SHI,GE,POINT:INTEGER:=0;
  SIGNAL FLAG:STD_LOGIC;
  BEGIN
    FLAG<='1' WHEN K4='1' ELSE
          '0';
    LC<=10*CONV_INTEGER(S1)+CONV_INTEGER(S0);
    LC_RATE<=INTEGER(10+R1*3+R2*(LC-6)) WHEN LC>6 AND FLAG='1' AND K5='0' ELSE
             INTEGER(10+R1*(LC-3)) WHEN LC>3 AND FLAG='1' AND K5='0' ELSE
             10 WHEN FLAG='1' AND K5='0' ELSE
             INTEGER(15+R3*3+R4*(LC-6)) WHEN LC>6 AND FLAG='1' AND K5='1' ELSE
             INTEGER(15+R3*(LC-3)) WHEN LC>3 AND FLAG='1' AND K5='1' ELSE
             15 WHEN FLAG='1' AND K5='1' ELSE
             0;
    DD_RATE<=INTEGER(R1*CONV_INTEGER(W)) WHEN FLAG='1' AND K5='0' ELSE
             INTEGER(R3*CONV_INTEGER(W)) WHEN FLAG='1' AND K5='1' ELSE
             0;
    RATE<=LC_RATE+DD_RATE;
    BAI<=INTEGER(RATE) / 100;
    SHI<=INTEGER(RATE-100*BAI) / 10;
    GE<=INTEGER(RATE-100*BAI-10*SHI) / 1;
    POINT<=INTEGER(RATE-100*BAI-10*SHI-1*GE);
    Y0<=CONV_STD_LOGIC_VECTOR(POINT,4);
    Y1<=CONV_STD_LOGIC_VECTOR(GE,4);
    Y2<=CONV_STD_LOGIC_VECTOR(SHI,4);
    Y3<=CONV_STD_LOGIC_VECTOR(BAI,4) WHEN BAI/=0 ELSE
        "1111";
  END;