--------------------------------------------------------------------------
--  Crypto Chip
--  Copyright (C) 1999, Projektgruppe WS98/99
--  University of Stuttgart / Department of Computer Science / IFI-RA
--------------------------------------------------------------------------
-- Designers : Thomas Schwarz
-- Group     : RSA
--------------------------------------------------------------------
-- Design Unit Name : CALC_Qi
-- Purpose :  Calculates the next quotient digit during SRT-Division
--            inside the Montgomery circuit
-- 
-- File Name : calc_qi.vhd
--------------------------------------------------------------------
-- Simulator : SYNOPSYS VHDL System Simulator (VSS) Version 3.2.a
--------------------------------------------------------------------
-- Date            | Changes
-- 27.12.98        | 27.12.98
--                 |
-----------------------------------------------------------------------

--------------------------------------------------------------------------
--  Was implementiert wird
--  Berechnet das naechste Quotienten-Bit fuer die SRT_Division
--------------------------------------------------------------------------

library IEEE;
  use IEEE.std_logic_1164.all;
  use IEEE.std_logic_arith.all;
  use IEEE.std_logic_unsigned.all;



entity CALC_Qi is
  port( signal RC : in std_logic_vector(766 downto 763);
	signal RS : in std_logic_vector(767 downto 764);
	signal QiMINUS, QiPLUS : out std_logic
      );
end CALC_Qi;



architecture RTL of CALC_Qi is
    signal signature : std_logic_vector(7 downto 0);
begin 
    signature(7 downto 4) <= RC(766 downto 763);
    signature(3 downto 0) <= RS(767 downto 764);
    with signature select
        QiMINUS <=
        '1' when "00000001"|"00000010"|"00000011"|"00000100"
                |"00000101"|"00000110"|"00000111"|"00010000"
                |"00010001"|"00010010"|"00010011"|"00010100"
                |"00010101"|"00010110"|"00100000"|"00100001"
                |"00100010"|"00100011"|"00100100"|"00100101"
                |"00101111"|"00110000"|"00110001"|"00110010"
                |"00110011"|"00110100"|"00111110"|"00111111"
                |"01000000"|"01000001"|"01000010"|"01000011"
                |"01001101"|"01001110"|"01001111"|"01010000"
                |"01010001"|"01010010"|"01011100"|"01011101"
                |"01011110"|"01011111"|"01100000"|"01100001"
                |"01101011"|"01101100"|"01101101"|"01101110"
                |"01101111"|"01110000"|"01111010"|"01111011"
                |"01111100"|"01111101"|"01111110"|"01111111"
                |"10001001"|"10001010"|"10001011"|"10001100"
                |"10001101"|"10001110"|"10001111"|"10011000"
                |"10011001"|"10011010"|"10011011"|"10011100"
                |"10011101"|"10011110"|"10100111"|"10101000"
                |"10101001"|"10101010"|"10101011"|"10101100"
                |"10101101"|"10110110"|"10110111"|"10111000"
                |"10111001"|"10111010"|"10111011"|"10111100"
                |"11000101"|"11000110"|"11000111"|"11001000"
                |"11001001"|"11001010"|"11001011"|"11010100"
                |"11010101"|"11010110"|"11010111"|"11011000"
                |"11011001"|"11011010"|"11100011"|"11100100"
                |"11100101"|"11100110"|"11100111"|"11101000"
                |"11101001"|"11110010"|"11110011"|"11110100"
                |"11110101"|"11110110"|"11110111"|"11111000",
        '0' when others;
    with signature select
        QiPLUS <=
        '1' when "00001000"|"00001001"|"00001010"|"00001011"
                |"00001100"|"00001101"|"00001110"|"00010111"
                |"00011000"|"00011001"|"00011010"|"00011011"
                |"00011100"|"00011101"|"00100110"|"00100111"
                |"00101000"|"00101001"|"00101010"|"00101011"
                |"00101100"|"00110101"|"00110110"|"00110111"
                |"00111000"|"00111001"|"00111010"|"00111011"
                |"01000100"|"01000101"|"01000110"|"01000111"
                |"01001000"|"01001001"|"01001010"|"01010011"
                |"01010100"|"01010101"|"01010110"|"01010111"
                |"01011000"|"01011001"|"01100010"|"01100011"
                |"01100100"|"01100101"|"01100110"|"01100111"
                |"01101000"|"01110001"|"01110010"|"01110011"
                |"01110100"|"01110101"|"01110110"|"01110111"
                |"10000000"|"10000001"|"10000010"|"10000011"
                |"10000100"|"10000101"|"10000110"|"10010000"
                |"10010001"|"10010010"|"10010011"|"10010100"
                |"10010101"|"10011111"|"10100000"|"10100001"
                |"10100010"|"10100011"|"10100100"|"10101110"
                |"10101111"|"10110000"|"10110001"|"10110010"
                |"10110011"|"10111101"|"10111110"|"10111111"
                |"11000000"|"11000001"|"11000010"|"11001100"
                |"11001101"|"11001110"|"11001111"|"11010000"
                |"11010001"|"11011011"|"11011100"|"11011101"
                |"11011110"|"11011111"|"11100000"|"11101010"
                |"11101011"|"11101100"|"11101101"|"11101110"
                |"11101111"|"11111001"|"11111010"|"11111011"
                |"11111100"|"11111101"|"11111110"|"11111111",
        '0' when others;
end RTL;