Subversion Repositories qfp32

-- Copyright (c) 2013 Malte Graeper (mgraep@t-online.de) All rights reserved.

-------------------------------------------------------------------------------

-- Carry lookahead adder library

-- provides all functions for making carry lookahead adder of

-- arbitary deepth and width

-------------------------------------------------------------------------------

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

package cla_p is

  type cla_group_t is record

          pro    : std_ulogic;

          gen    : std_ulogic;

  end record;

  type cla_level_t is array (natural range <>) of cla_group_t;

  function CLAGroupMk (

    a : unsigned;

    b : unsigned)

    return cla_group_t;

  function CLAGroupMk (

    level : cla_level_t)

    return cla_group_t;

  function CLALevelMk (

    a : unsigned;

    b : unsigned;

    group_size : natural)

    return cla_level_t;

  function CLALevelMk (

    level : cla_level_t;

    group_size : natural)

    return cla_level_t;

  -- purpose: propagates carry through groups and returns expanded carry vector

  function CLAExpandCy (

    level : cla_level_t;

    cy_in : std_ulogic)

    return std_ulogic_vector;

  function CLAExpandCy (

    level : cla_level_t;

    cy_in  : std_ulogic_vector)

    return std_ulogic_vector;

  -- purpose: adds vector a and b with using carry information from groups

  function CLAParallelAdd (

    a : unsigned;

    b : unsigned;

    cy_in : std_ulogic_vector)

    return unsigned;

end cla_p;

package body cla_p is

  function min(

    a : natural;

    b : natural)

    return natural is

  begin

    if a > b then

      return b;

    else

      return a;

    end if;

  end min;

  function CLAGroupMk (

    a : unsigned;

    b : unsigned)

    return cla_group_t is

    variable gen : std_ulogic;

    variable pro : std_ulogic;

  begin

    gen := '0';

    pro := '1';

    for i in a'length-1 downto 0 loop

      gen := (a(i) and b(i) and pro) or gen;

      pro := (a(i) or b(i)) and pro;

    end loop;

    return (pro,gen);

  end CLAGroupMk;

  function CLAGroupMk (

    level : cla_level_t)

    return cla_group_t is

    variable gen : std_ulogic;

    variable pro : std_ulogic;

  begin

    gen := '0';

    pro := '1';

    for i in level'length-1 downto 0 loop

      -- calc propagate/generate

      gen := (level(i).gen  and pro) or gen;

      pro := level(i).pro and pro;

    end loop;

    return (pro,gen);

  end CLAGroupMk;

  function CLALevelMk (

    a : unsigned;

    b : unsigned;

    group_size : natural)

    return cla_level_t is

    variable lb,ub : natural;

    variable slice_a,slice_b : unsigned(group_size-1 downto 0);

    variable level : cla_level_t((a'length-1)/group_size downto 0);

  begin

    for i in 0 to (a'length-1)/group_size loop

      lb := i*group_size;

      ub := min(lb+group_size,a'length)-1;

      slice_a(ub-lb downto 0) := a(ub downto lb);

      slice_b(ub-lb downto 0) := b(ub downto lb);

      level(i) := CLAGroupMk(slice_a(ub-lb downto 0),slice_b(ub-lb downto 0));

   end loop;

   return level;

  end CLALevelMk;

  function CLALevelMk (

    level : cla_level_t;

    group_size : natural)

    return cla_level_t is

    variable lb,ub : natural;

    variable slice : cla_level_t(group_size-1 downto 0);

    variable level_out : cla_level_t((level'length-1)/group_size downto 0);

  begin

    for i in 0 to (level'length-1)/group_size loop

      lb := i*group_size;

      ub := min(lb+group_size,level'length)-1;

      slice(ub-lb downto 0) := level(ub downto lb);

      level_out(i) := CLAGroupMk(slice(ub-lb downto 0));

    end loop;

    return level_out;

  end CLALevelMk;

  -- purpose: propagates carry through group and returns expanded carry vector

  function CLAExpandCy (

    level : cla_level_t;

    cy_in  : std_ulogic)

    return std_ulogic_vector is

    variable cy : std_ulogic;

    variable cy_out : std_ulogic_vector(level'length downto 0);

  begin  -- CLAExpandCy

    cy := cy_in;

    cy_out(0) := cy;

    for i in 0 to level'length-1 loop

      cy := level(i).gen or (level(i).pro and cy);

      cy_out(i+1) := cy;

    end loop;  -- i     

    return cy_out;

  end CLAExpandCy;

  -- purpose: propagates carry through each group (maybe more than one) and returns expanded carry vector

  function CLAExpandCy (

    level : cla_level_t;

    cy_in  : std_ulogic_vector)

    return std_ulogic_vector is

    constant group_size : natural := 1+(level'length-1)/(cy_in'length-1);  -- length cy_in = number of groups+1          

    variable ub,lb : natural;

    variable slice : cla_level_t(group_size-1 downto 0);

    variable cy_out : std_ulogic_vector(level'length downto 0);

  begin  -- CLAExpandCy  

    cy_out(cy_out'length-1) := cy_in(cy_in'length-1);

    for i in 0 to (level'length-1)/group_size loop

      lb := i*group_size;

      ub := min(lb+group_size,level'length)-1;

      slice(ub-lb downto 0) := level(ub downto lb);

      cy_out(ub downto lb) := CLAExpandCy(slice(ub-lb downto 0),cy_in(i))(ub-lb downto 0);

    end loop;

    return cy_out;

  end CLAExpandCy;

  -- purpose: adds vector a and b with using carry information from groups

  function CLAParallelAdd (

    a : unsigned;

    b : unsigned;

    cy_in : std_ulogic_vector)

    return unsigned is

    constant adder_size : integer := 1+(a'length-1)/(cy_in'length-1);

    variable lb,ub : natural;

    variable result : unsigned(a'length-1 downto 0);

    variable cy_vec : std_ulogic_vector(adder_size-1 downto 0) := (others => '0');

  begin  -- CLAParallelAdd

    result := to_unsigned(0,result'length);

    for i in 0 to (a'length-1)/adder_size loop

      lb := i*adder_size;

      ub := min(lb+adder_size,a'length)-1;

      cy_vec(0) := cy_in(i);

      result(ub downto lb) := a(ub downto lb)+b(ub downto lb)+unsigned(cy_vec(ub-lb downto 0));

    end loop;  -- i     

    return result;

  end CLAParallelAdd;

end package body cla_p;