CREATE GLOBAL TEMPORARY TABLE GTT$LVN (
    ID        INTEGER,
    LVNVALUE  INTEGER
) ON COMMIT DELETE ROWS;

CREATE OR ALTER PROCEDURE LVNMIN3 (
    A INTEGER,
    B INTEGER,
    C INTEGER)
RETURNS (
    AMIN INTEGER)
AS
begin
  amin=a;
  if (b<amin) then amin=b;
  if (c<amin) then amin=c;
  suspend;
end

CREATE OR ALTER PROCEDURE LVNDIST (
    S VARCHAR(1024),
    T VARCHAR(1024))
RETURNS (
    DIST INTEGER)
AS
declare variable i integer;
declare variable j integer;
declare variable m integer;
declare variable n integer;
declare variable cost integer;
declare variable flip smallint;
declare variable cuthalf integer;
declare variable b1 integer;
declare variable b2 integer;
declare variable b3 integer;
begin
  s=upper(s);
  t=upper(t);

  cuthalf=2048;
  i=0;
  while (i<=2048) do
    begin
       insert into gtt$lvn(id,lvnvalue) values (:i,0);
       i=i+1;
    end

  cuthalf=1024;

  s=substring(s from 1 for cuthalf-1);
  t=substring(t from 1 for cuthalf-1);
  m=char_length(s);
  n=char_length(t);

  if (m=0) then dist=n;
  else
  if (n=0) then dist=m;
  else
     begin
       flip=0; -- false;
       i=0;
       while (i<=n) do
         begin
           update gtt$lvn set lvnvalue=:i where id=:i;
           i=i+1;
         end

       i=1;
       while (i<=m) do
          begin
            if (flip=1) then
               update gtt$lvn set lvnvalue=:i where id=0;
            else
               update gtt$lvn set lvnvalue=:i where id=:cuthalf;

            j=1;
            while (j<=n) do
               begin
                 if (substring(s from :i for 1)=substring(t from :i for 1)) then cost=0;
                 else cost=1;

                 if (flip=1) then
                     begin
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:cuthalf+:j into :b1;
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:j-1 into :b2;
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:cuthalf+:j-1 into :b3;

                        select lvnmin3.amin from lvnmin3(:b1+1,:b2+1,:b3+:cost) into :b1;

                        update gtt$lvn set lvnvalue=:b1 where id=:j;
                     end
                 else begin
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:j into :b1;
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:cuthalf+:j-1 into :b2;
                        select gtt$lvn.lvnvalue from gtt$lvn where gtt$lvn.id=:j-1 into :b3;

                        select lvnmin3.amin from lvnmin3(:b1+1,:b2+1,:b3+:cost) into :b1;

                        update gtt$lvn set lvnvalue=:b1 where id=:cuthalf+:j;
                      end

                j=j+1;
              end

        if (flip=1) then flip=0;
        else flip=1;

        i=i+1;
     end

       if (flip=1) then
          select gtt$lvn.lvnvalue from gtt$lvn where id=:cuthalf+:n into :dist;
       else
          select gtt$lvn.lvnvalue from gtt$lvn where id=:n into :dist;

    end
  suspend;
end