{$mode objfpc}
{$h+}
unit bzip2stream;
{****************************************************************************

                             BZIP2 decompression unit

                        Copyright (C) 2002 by Daniel Mantione
                        Class port (C) 2009 by Michael Van Canneyt

This unit provides a decompression stream to decode .bz2 files. It is
inpired by Julian R. Seward's libbzip2 library and therefore you should
send credits to him and bug reports to me :)

This code is licensed under the same terms as the original libbz2 library,
which is decsribed in the file LICENSE. If you don't have this file, look
at http://www.freepascal.org for this bzip2 unit, the LICENSE file will
be included. In case of problems, contact the author.

E-mail addresses:

Michael Van Canneyt <michael@freepascal.org>
Daniel Mantione     <daniel.mantione@freepascal.org>
Julian R. Seward    <jseward@acm.org>

Please do not contact Julian about this Pascal library, he didn't wrote it.

****************************************************************************}
interface

{$goto on}

uses Classes,SysUtils, bzip2comn;

Type
  TDecompressBzip2Stream=Class(TOwnerStream)
  Private
    block_randomized:boolean;
    blocksize:byte;
    tt:Pcardinal_array;
    tt_count:cardinal;
    rle_run_left,rle_run_data:byte;
    nextrle:Pbyte;
    decode_available:cardinal;
    block_origin:cardinal;
    current_block:cardinal;
    read_data,bits_available:byte;
    inuse16:set of 0..15;
    inuse:set of 0..255;
    inuse_count:cardinal;
    seq_to_unseq:array[0..255] of byte;
    alphasize:cardinal;
    group_count,group_pos,gsel,gminlen:byte;
    group_no:cardinal;
    glimit,gperm,gbase:Phuffarray;
    selector_count:cardinal;
    selector,selector_mtf:array[0..max_selectors] of byte;
    len:array[0..max_groups,0..max_alpha_size] of byte;
    limit:array[0..max_groups,0..max_alpha_size] of cardinal;
    base:array[0..max_groups,0..max_alpha_size] of cardinal;
    perm:array[0..max_groups,0..max_alpha_size] of cardinal;
    minlens:array[0..max_groups] of byte;
    cftab:array[0..257] of cardinal;
    mtfbase:array[0..256 div mtfl_size-1] of cardinal;
    mtfa:array[0..mtfa_size-1] of byte;
    
    function get_bits(n:byte):byte;
    function get_boolean:boolean;
    function get_byte:byte;
    function get_cardinal24:cardinal;
    function get_cardinal:cardinal;
    procedure receive_mapping_table;
    procedure receive_selectors;
    procedure undo_mtf_values;
    procedure receive_coding_tables;
    procedure make_hufftab;
    procedure init_mtf;
    function get_mtf_value:cardinal;
    procedure move_mtf_block;
    procedure receive_mtf_values;
    procedure detransform;
    function decode_block : boolean;
    Function new_block : boolean;
    Function consume_rle : Boolean; inline;
    Function rle_read(bufptr:Pbyte;count:Longint) : longint;
    Procedure Error(Msg : String; ACode : Integer);
  Public  
    Constructor Create(ASource : TStream);
    Destructor Destroy; override;
    function Read(var Buffer; Count: Longint): Longint; override;
  end;
  
  EBzip2 = Class(Exception)
    ErrCode : Integer;
  end;

implementation

{$ifdef cpui386}
  {$i bzip2si386.inc}
{$endif}

{*****************************************************************************
                             TDecompressBzip2Stream
*****************************************************************************}

Resourcestring
  BZip2Initialize   = 'Invalid BZip2 stream: invalid header';
  SDecodingError    = 'Decoding error';
  SErrUnimplemented = 'Feature not implemented';
  
Constructor TDecompressBzip2Stream.Create(ASource: TStream);

var magic:array[1..3] of char;
    c:char;

begin
  Inherited Create(ASource);
  {Read the magic.}
  Source.ReadBuffer(magic,sizeof(magic));
  if magic<>bzip2_stream_magic then
    Error(BZip2Initialize,bzip2_bad_header_magic);
  {Read the block size and allocate the working array.}
  Source.ReadBuffer(c,1);
  blocksize:=byte(c)-byte('0');
  GetMem(tt,blocksize*100000*sizeof(cardinal));
  decode_available:=high(decode_available);
end;

Procedure TDecompressBzip2Stream.Error(Msg : String; ACode : Integer);

Var
  BE : EBzip2;

begin
  BE:=EBzip2.Create(Msg);
  BE.ErrCode:=ACode;
  Raise BE;
end;
   
function TDecompressBzip2Stream.get_bits(n:byte):byte;

var data:byte;

begin
  if n>bits_available then
    begin
      Source.ReadBuffer(data,1);
      get_bits:=(read_data shr (8-n)) or data shr (8-(n-bits_available));
      read_data:=byte(data shl (n-bits_available));
      inc(bits_available,8);
    end
  else
    begin
      get_bits:=read_data shr (8-n);
      read_data:=byte(read_data shl n);
    end;
  dec(bits_available,n);
end;

function TDecompressBzip2Stream.get_boolean:boolean;

begin
  get_boolean:=boolean(get_bits(1));
end;

function TDecompressBzip2Stream.get_byte:byte;

begin
  get_byte:=get_bits(8);
end;

function TDecompressBzip2Stream.get_cardinal24:cardinal;

begin
  get_cardinal24:=get_bits(8) shl 16 or get_bits(8) shl 8 or get_bits(8);
end;


function TDecompressBzip2Stream.get_cardinal:cardinal;

begin
  get_cardinal:=get_bits(8) shl 24 or get_bits(8) shl 16 or get_bits(8) shl 8 or
                get_bits(8);
end;

procedure TDecompressBzip2Stream.receive_mapping_table;

{Receive the mapping table. To save space, the inuse set is stored in pieces
 of 16 bits. First 16 bits are stored which pieces of 16 bits are used, then
 the pieces follow.}

var i,j:byte;

begin
  inuse16:=[];
  {Receive the first 16 bits which tell which pieces are stored.}
  for i:=0 to 15 do
    if get_boolean then
      include(inuse16,i);

  {Receive the used pieces.}
  inuse:=[];
  inuse_count:=0;
  for i:=0 to 15 do
    if i in inuse16 then
      for j:=0 to 15 do
        if get_boolean then
          begin
            include(inuse,16*i+j);
            seq_to_unseq[inuse_count]:=16*i+j;
            inc(inuse_count);
          end;
{  system.write('Mapping table: ');
  for i:=0 to 255 do
    if i in inuse then
      system.write(i,' ');
  writeln;}
end;

procedure TDecompressBzip2Stream.receive_selectors;

{Receives the selectors.}

var i:cardinal;
    j:byte;

begin
  group_count:=get_bits(3);
  selector_count:=get_bits(8) shl 7 or get_bits(7);
  for i:=0 to selector_count-1 do
    begin
      j:=0;
      while get_boolean do
        begin
          inc(j);
          if j>5 then
            error(SDecodingError,bzip2_data_error);
        end;
      selector_mtf[i]:=j;
    end;
{  system.write('Selector_mtf: ');
  for i:=0 to selector_count-1 do
    system.write(selector_mtf[i],' ');
  writeln;}
end;

procedure TDecompressBzip2Stream.undo_mtf_values;

{Undo the MTF values for the selectors.}

var pos:array[0..max_groups] of byte;
    i:cardinal;
    v,tmp:byte;

begin
  for v:=0 to group_count-1 do
    pos[v]:=v;
  for i:=0 to selector_count-1 do
    begin
      v:=selector_mtf[i];
      tmp:=pos[v];
      while v<>0 do
        begin
          pos[v]:=pos[v-1];
          dec(v);
        end;
      pos[0]:=tmp;
      selector[i]:=tmp;
    end;
end;

procedure TDecompressBzip2Stream.receive_coding_tables;

var t,curr:byte;
    i:cardinal;

begin
  for t:=0 to group_count-1 do
    begin
      curr:=get_bits(5);
      for i:=0 to alphasize-1 do
        begin
          repeat
            if not(curr in [1..20]) then
              error(SDecodingError,bzip2_data_error);
            if not get_boolean then
              break;
            if get_boolean then
              dec(curr)
            else
              inc(curr);
          until false;
          len[t,i]:=curr;
        end;
    end;
end;

procedure TDecompressBzip2Stream.make_hufftab;

{Builds the Huffman tables.}

var i:cardinal;
    t,minlen,maxlen:byte;

begin
  for t:=0 to group_count-1 do
    begin
      minlen:=32;
      maxlen:=0;
      for i:=0 to alphasize-1 do
        begin
          if len[t,i]>maxlen then
            maxlen:=len[t,i];
          if len[t,i]<minlen then
            minlen:=len[t,i];
        end;
      hb_create_decode_tables(limit[t],base[t],perm[t],len[t],
                              minlen,maxlen,alphasize);
      minlens[t]:=minlen;
    end;
end;

procedure TDecompressBzip2Stream.init_mtf;

var i,j:byte;
    k:cardinal;

begin
  k:=mtfa_size-1;
  for i:=256 div mtfl_size-1 downto 0 do
    begin
      for j:=mtfl_size-1 downto 0 do
        begin
          mtfa[k]:=i*mtfl_size+j;
          dec(k);
        end;
      mtfbase[i]:=k+1;
    end;
end;

function TDecompressBzip2Stream.get_mtf_value:cardinal;

var zn:byte;
    zvec:cardinal;

begin
  if group_pos=0 then
    begin
      inc(group_no);
      group_pos:=group_size;
      gsel:=selector[group_no];
      gminlen:=minlens[gsel];
      glimit:=@limit[gsel];
      gperm:=@perm[gsel];
      gbase:=@base[gsel];
    end;
  dec(group_pos);
  zn:=gminlen;
  zvec:=get_bits(zn);
  while zvec>glimit^[zn] do
    begin
      inc(zn);
      zvec:=zvec shl 1 or byte(get_boolean);
    end;
  get_mtf_value:=gperm^[zvec-gbase^[zn]];
end;

procedure TDecompressBzip2Stream.move_mtf_block;

var i:byte;
    j,k:cardinal;

begin
  k:=MTFA_SIZE;
  for i:=256 div MTFL_SIZE-1 downto 0 do
    begin
      j:=mtfbase[i];
      Pcardinal(@mtfa[k- 4])^:=Pcardinal(@mtfa[j+12])^;
      Pcardinal(@mtfa[k- 8])^:=Pcardinal(@mtfa[j+ 8])^;
      Pcardinal(@mtfa[k-12])^:=Pcardinal(@mtfa[j+ 4])^;
      dec(k,16);
      Pcardinal(@mtfa[k   ])^:=Pcardinal(@mtfa[j   ])^;
      mtfbase[i]:=k;
    end;
end;

procedure TDecompressBzip2Stream.receive_mtf_values;

const run_a=0;
      run_b=1;

var t,next_sym:cardinal;
    es:cardinal;
    n:byte;
    nn,i:cardinal;
    p,q:Pbyte;
    u,v:Pcardinal;
    lno,off:cardinal;

begin
  group_no:=high(group_no);
  group_pos:=0;
  t:=0;
  for i:=0 to 257 do
    cftab[i]:=0;
  init_mtf;
  next_sym:=get_mtf_value;
  while next_sym<>inuse_count+1 do
    begin
{      writeln(t,'   ',next_sym);
      if t=22296 then
        t:=t;                    }
      if next_sym<=run_b then
        begin
          es:=0;
          n:=0;
          repeat
            inc(es,(next_sym+1) shl n);
            inc(n);
            next_sym:=get_mtf_value;
          until next_sym>run_b;
          n:=seq_to_unseq[mtfa[mtfbase[0]]];
          inc(cftab[n],es);
          if t+es>100000*blocksize then
            error(SDecodingError,bzip2_data_error);
          while es>0 do
            begin
              tt^[t]:=n;
              dec(es);
              inc(t);
            end;
        end
      else
        begin
          nn:=next_sym-1;
          if nn<mtfl_size then
            begin
              {Avoid the costs of the general case.}
              p:=@mtfa[mtfbase[0]];
              q:=p+nn;
              n:=q^;
              repeat
                q^:=(q-1)^;
                dec(q);
              until q=p;
              q^:=n;
            end
          else
            begin
              {General case.}
              lno:=nn div MTFL_SIZE;
              off:=nn and (MTFL_SIZE-1);
              p:=@mtfa[mtfbase[lno]];
              q:=p+off;
              n:=q^;
              while(q<>p) do
                begin
                  q^:=(q-1)^;
                  dec(q);
                end;
              u:=@mtfbase;
              v:=u+lno;
              repeat
                mtfa[v^]:=mtfa[(v-1)^+MTFL_SIZE-1];
                dec(v);
                dec(v^);
              until v=u;
              mtfa[v^]:=n;
              if v^=0 then
                move_mtf_block;
            end;
          inc(cftab[seq_to_unseq[n]]);
          tt^[t]:=cardinal(seq_to_unseq[n]);
          inc(t);
          if t>100000*blocksize then
            error(SDecodingError,bzip2_data_error);
          next_sym:=get_mtf_value;
        end;
    end;
    tt_count:=t;
  {Setup cftab to facilitate generation of T^(-1).}
  t:=0;
  for i:=0 to 256 do
    begin
      nn:=cftab[i];
      cftab[i]:=t;
{      writeln(i,' ',t);}
      inc(t,nn);
    end;
end;

{$ifndef HAVE_DETRANSFORM}

procedure TDecompressBzip2Stream.detransform;

var a:cardinal;
    p,q,r:Pcardinal;

begin
  a:=0;
  p:=@tt^[0];
  q:=p+tt_count;
  while p<>q do
    begin
      r:=@tt^[cftab[p^ and $ff]];
      inc(cftab[p^ and $ff]);
      r^:=r^ or a;
      inc(a,256);
      inc(p);
    end;
end;

{$endif}

function TDecompressBzip2Stream.decode_block:boolean;

{Decode a new compressed block.}

var magic:array[1..6] of char;
    stored_blockcrc:cardinal;
    i:byte;

begin
  for i:=1 to 6 do
    magic[i]:=char(get_byte);
  if magic='1AY&SY' then
    begin
      inc(current_block);
      stored_blockcrc:=get_cardinal;
      block_randomized:=get_boolean;
      block_origin:=get_cardinal24;

      {Receive the mapping table.}
      receive_mapping_table;
      alphasize:=cardinal(inuse_count)+2;
      
      {Receive the selectors. Raises exception}
      receive_selectors;
      {Undo the MTF values for the selectors.}
      undo_mtf_values;
      {Receive the coding tables.}
      receive_coding_tables;
      {Build the Huffman tables.}
      make_hufftab;
      {Receive the MTF values.}
      receive_mtf_values;
      {Undo the Burrows Wheeler transformation.}
      detransform;
      decode_available:=tt_count;
      Result:=True;
    end
  else
    begin
      if magic<>#$17'rE8P'#$90 then
        error(SDecodingError,bzip2_bad_block_magic);
      Result:=false;
    end;
end;

Function TDecompressBzip2Stream.new_block : Boolean;

begin
  Result:=decode_block;
  If result then
    nextrle:=@tt^[tt^[block_origin] shr 8]
  else
    nextrle:=nil;
end;

Function TDecompressBzip2Stream.consume_rle : Boolean;inline;

{Make nextrle point to the next decoded byte. If nextrle did point to the last
 byte in the current block, decode the next block.}

begin
{  Pcardinal(nextrle)^:=Pcardinal(nextrle)^ shr 8;}
  nextrle:=@tt^[Pcardinal(nextrle)^ shr 8];
  dec(decode_available);
  if decode_available=0 then
    Result:=new_block
  else
    Result:=True;  
end;

Function TDecompressBzip2Stream.rle_read(bufptr:Pbyte;Count:Longint) : LongInt;

var rle_len:cardinal;
    data:byte;

label rle_write;

begin
  Result:=0;
  rle_len:=rle_run_left;
  data:=rle_run_data;
  if block_randomized then
    {Not yet implemented.}
    Error(SErrUnimplemented,-1)
  else
    begin
      if rle_len<>0 then
        {Speed is important. Instead of an if statement within the
         repeat loop use a goto outside the loop.}
        goto rle_write;
      repeat
        if decode_available=0 then
          break;
        rle_len:=1;
        data:=nextrle^;
        if consume_rle and (decode_available>0) and (data=nextrle^) then
          begin
            inc(rle_len);
            if consume_rle and (decode_available>0) and (data=nextrle^) then
              begin
                inc(rle_len);
                if consume_rle and (decode_available>0) and (data=nextrle^) then
                  begin
                  if consume_rle then
                    inc(rle_len,nextrle^+1);
                  consume_rle;
                  end;
                end;
            end;
rle_write:
        repeat
            bufptr^:=data;
            inc(bufptr);
            dec(count);
            dec(rle_len);
            inc(Result);
        until (rle_len=0) or (count=0);
      until count=0;
    end;
  rle_run_data:=data;
  rle_run_left:=rle_len;
end;

Function TDecompressBzip2Stream.Read(var Buffer; Count : Longint) : LongInt;

var bufptr:Pbyte;

begin
  bufptr:=@buffer;
  if decode_available=high(decode_available) then
    begin
      {Initialize the rle process:
        - Decode a block
        - Initialize pointer.}
      if not decode_block then
        begin
        nextrle:=nil;
        error(SDecodingError,bzip2_endoffile);
        end;
      nextrle:=@tt^[tt^[block_origin] shr 8];
    end;
  Result:=rle_read(bufptr,count);
end;

Destructor TDecompressBzip2Stream.Destroy;

begin
  if tt<>nil then
    FreeMem(tt,blocksize*100000*sizeof(cardinal));
  Inherited;
end;

end.
