------------------------------------------------------------
-- Square Root Calculator   (FLEX10k)
-- < fpsqrt.vhd >
-- 1998/11/11 (Wed) 
-- yamaoka@tube.ee.uec.ac.jp
------------------------------------------------------------
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.all;

package MATH is
	function sqrt( FA : std_logic_vector ) return std_logic_vector;
end MATH;

package body MATH is
	function sqrt( FA : std_logic_vector ) return std_logic_vector is 
	variable MA : std_logic_vector(25 downto 0);
	variable MQ : std_logic_vector(24 downto 0);
	variable EQ : std_logic_vector(7 downto 0);
	variable TMP1, TMP2, REMAIN : std_logic_vector(27 downto 0);
begin

EQ := FA(30 downto 23) - "01111111";
EQ := ( EQ(7) & EQ(7 downto 1) ) + "01111111";

if FA(23) = '1' then
	MA := "01" & FA(22 downto 0) & '0';
else 
	MA := '1' & FA(22 downto 0) & "00";
end if;

TMP1 := "00000000000000000000000000" & MA( 25 downto 24 ); 
TMP2 := "0000000000000000000000000001";

for I in 0 to 24 loop
	REMAIN := TMP1 - TMP2;
	if REMAIN(27) = '0' then
		MQ(24-I) := '1';
		if I <= 11 then
			TMP1( (I+3) downto 0 ) := REMAIN( (I+1) downto 0 ) & MA( (23-(2*I)) downto (22-(2*I)));
		else 
			TMP1( (I+3) downto 0 ) := REMAIN( (I+1) downto 0 ) & "00";
		end if;
		TMP2( (I+3) downto 0 ) := TMP2( (I+2) downto 1 ) & "01";
		TMP2(2) := '1';
	else
		MQ(24-I) := '0';
		if I <= 11 then
			TMP1( (I+3) downto 0 ) := TMP1( (I+1) downto 0 ) & MA( (23-(2*I)) downto (22-(2*I)));
		else
			TMP1( (I+3) downto 0 ) := TMP1( (I+1) downto 0 ) & "00";
		end if;	
		TMP2( (I+3) downto 0 ) := TMP2( ( I+2 ) downto 1) & "01";
	end if;
end loop;
MQ := MQ + "0000000000000000000000001";
return '0' & EQ & MQ(23 downto 1);
end sqrt;
end MATH;