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+
+-- Copyright (C) 1996 Morgan Kaufmann Publishers, Inc
+
+-- This file is part of VESTs (Vhdl tESTs).
+
+-- VESTs is free software; you can redistribute it and/or modify it
+-- under the terms of the GNU General Public License as published by the
+-- Free Software Foundation; either version 2 of the License, or (at
+-- your option) any later version.
+
+-- VESTs is distributed in the hope that it will be useful, but WITHOUT
+-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+-- FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+-- for more details.
+
+-- You should have received a copy of the GNU General Public License
+-- along with VESTs; if not, write to the Free Software Foundation,
+-- Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+-- ---------------------------------------------------------------------
+--
+-- $Id: ch_06_mult-b.vhd,v 1.2 2001-10-26 16:29:34 paw Exp $
+-- $Revision: 1.2 $
+--
+-- ---------------------------------------------------------------------
+
+architecture behavioral of multiplier is
+begin
+
+ behavior : process (a, b) is
+
+ constant Tpd_in_out : time := 40 ns;
+ variable negative_result : boolean;
+ variable op1 : std_ulogic_vector(15 downto 0);
+ variable op2 : std_ulogic_vector(15 downto 0);
+ variable result : std_ulogic_vector(31 downto 0);
+ variable carry_in, carry : std_ulogic;
+
+ begin
+ op1 := to_X01(a);
+ op2 := to_X01(b);
+ -- make both operands positive, remembering sign of result
+ negative_result := (op1(15) = '1') xor (op2(15) = '1');
+ if (op1(15) = '1') then
+ carry := '1';
+ for index in 0 to 15 loop
+ carry_in := carry;
+ carry := carry_in and not op1(index);
+ op1(index) := not op1(index) xor carry_in;
+ end loop;
+ end if;
+ if (op2(15) = '1') then
+ carry := '1';
+ for index in 0 to 15 loop
+ carry_in := carry;
+ carry := carry_in and not op2(index);
+ op2(index) := not op2(index) xor carry_in;
+ end loop;
+ end if;
+ -- do long multiplication
+ result := (others => '0');
+ for count in 0 to 15 loop
+ carry := '0';
+ if (op2(count) = '1') then
+ for index in 0 to 15 loop
+ carry_in := carry;
+ carry := (result(index+count) and op1(index))
+ or (carry_in and (result(index+count) xor op1(index)));
+ result(index+count) := result(index+count) xor op1(index) xor carry_in;
+ end loop;
+ result(count+16) := carry;
+ end if;
+ end loop;
+ -- result now contains unsigned product, with binary point
+ -- between bits 30 and 29. assign output with sign adjusted.
+ if negative_result then
+ carry := '1';
+ for index in 0 to 31 loop
+ carry_in := carry;
+ carry := carry_in and not result(index);
+ result(index) := not result(index) xor carry_in;
+ end loop;
+ end if;
+ p <= result after Tpd_in_out;
+ end process behavior;
+
+end architecture behavioral;
+