32 bit alu design -dont think my loop is ok any suggestions?

[joe345]

32 bit alu design

Trying to perform addition on the op code 010 but i cant use + sign as the requirement for addition so im trying to perform it using a ripple carry half bit adder but i dont think my loop is ok. Because if i perform 011 + 111 i do get correct result.. any suggestions?




LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.std_logic_arith.ALL;
USE ieee.std_logic_unsigned.ALL;

ENTITY alu IS
PORT(
a : IN STD_LOGIC_VECTOR(31 DOWNTO 0);
b : IN STD_LOGIC_VECTOR(31 DOWNTO 0);
op : IN STD_LOGIC_VECTOR( 2 DOWNTO 0);
result : OUT STD_LOGIC_VECTOR(31 DOWNTO 0);
cout : OUT STD_LOGIC;
zero : OUT STD_LOGIC);
END alu;

ARCHITECTURE description OF alu IS BEGIN

SIGNAL carrytemp: std_logic

PROCESS(a,b,op)
BEGIN
carrytemp <= '0'
CASE op IS
WHEN "000" =>
result <= a AND b;
WHEN "001" =>
result <= a OR b;
WHEN "010" =>

for i in 31 downto 0

result(i) <= ((a(i) XOR b(i))+carrytemp);
carrytemp <= a(i) AND b(i);

end loop

cout <= carrytemp;

WHEN "110" =>

WHEN "011" =>
result <= a;
WHEN "111" =>
result <= b;
END CASE;
END PROCESS

END description;