------------------------------------------------------------------------------
-- Copyright (c) 2016, Natacha Porté --
-- --
-- Permission to use, copy, modify, and distribute this software for any --
-- purpose with or without fee is hereby granted, provided that the above --
-- copyright notice and this permission notice appear in all copies. --
-- --
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES --
-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF --
-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR --
-- ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES --
-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN --
-- ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF --
-- OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. --
------------------------------------------------------------------------------
package body Natools.Smaz is
use type Ada.Streams.Stream_Element_Offset;
procedure Find_Entry
(Dict : in Dictionary;
Template : in String;
Index : out Ada.Streams.Stream_Element;
Length : out Natural);
-- Try to find the longest entry in Dict that is a prefix of Template,
-- setting Length to 0 when no such entry exists.
function To_String (Data : in Ada.Streams.Stream_Element_Array)
return String;
-- Convert a stream element array into a string
function Verbatim_Size (Dict : Dictionary; Original_Size : Natural)
return Ada.Streams.Stream_Element_Count;
-- Return the number of bytes needed by the verbatim encoding
-- of Original_Size bytes.
------------------------------
-- Local Helper Subprograms --
------------------------------
procedure Find_Entry
(Dict : in Dictionary;
Template : in String;
Index : out Ada.Streams.Stream_Element;
Length : out Natural)
is
I : Ada.Streams.Stream_Element;
N : Natural;
begin
Index := Ada.Streams.Stream_Element'Last;
Length := 0;
for Last in reverse Template'Range loop
N := Dict.Hash (Template (Template'First .. Last));
if N <= Natural (Dict.Dict_Last) then
I := Ada.Streams.Stream_Element (N);
if Dict_Entry (Dict, I) = Template (Template'First .. Last) then
Index := I;
Length := 1 + Last - Template'First;
return;
end if;
end if;
end loop;
end Find_Entry;
function To_String (Data : in Ada.Streams.Stream_Element_Array)
return String is
begin
return Result : String (1 .. Data'Length) do
for I in Result'Range loop
Result (I) := Character'Val (Data
(Data'First + Ada.Streams.Stream_Element_Offset (I - 1)));
end loop;
end return;
end To_String;
function Verbatim_Size (Dict : Dictionary; Original_Size : Natural)
return Ada.Streams.Stream_Element_Count
is
Verbatim1_Max_Size : constant Ada.Streams.Stream_Element_Count
:= Ada.Streams.Stream_Element_Count
(Ada.Streams.Stream_Element'Last - Dict.Dict_Last)
- Boolean'Pos (Dict.Variable_Length_Verbatim);
Verbatim2_Max_Size : constant Ada.Streams.Stream_Element_Count
:= Ada.Streams.Stream_Element_Count (Ada.Streams.Stream_Element'Last)
+ Verbatim1_Max_Size;
Remaining : Ada.Streams.Stream_Element_Count
:= Ada.Streams.Stream_Element_Count (Original_Size);
Overhead : Ada.Streams.Stream_Element_Count := 0;
begin
if Dict.Variable_Length_Verbatim then
if Remaining >= Verbatim2_Max_Size then
declare
Full_Blocks : constant Ada.Streams.Stream_Element_Count
:= Remaining / Verbatim2_Max_Size;
begin
Overhead := Overhead + 2 * Full_Blocks;
Remaining := Remaining - Verbatim2_Max_Size * Full_Blocks;
end;
end if;
if Remaining > Verbatim1_Max_Size then
Overhead := Overhead + 2;
Remaining := 0;
end if;
end if;
declare
Full_Blocks : constant Ada.Streams.Stream_Element_Count
:= Remaining / Verbatim1_Max_Size;
begin
Overhead := Overhead + Full_Blocks;
end;
return Overhead + Ada.Streams.Stream_Element_Count (Original_Size);
end Verbatim_Size;
----------------------
-- Public Interface --
----------------------
function Dict_Entry
(Dict : in Dictionary;
Index : in Ada.Streams.Stream_Element)
return String
is
First : constant Positive := Dict.Offsets (Index);
Last : Natural := Dict.Values'Last;
begin
if Index + 1 in Dict.Offsets'Range then
Last := Dict.Offsets (Index + 1) - 1;
end if;
return Dict.Values (First .. Last);
end Dict_Entry;
function Compressed_Upper_Bound
(Dict : in Dictionary;
Input : in String)
return Ada.Streams.Stream_Element_Count is
begin
return Verbatim_Size (Dict, Input'Length);
end Compressed_Upper_Bound;
procedure Compress
(Dict : in Dictionary;
Input : in String;
Output_Buffer : out Ada.Streams.Stream_Element_Array;
Output_Last : out Ada.Streams.Stream_Element_Offset)
is
procedure Find_Entry;
Verbatim1_Max_Size : constant Natural
:= Natural (Ada.Streams.Stream_Element'Last - Dict.Dict_Last)
- Boolean'Pos (Dict.Variable_Length_Verbatim);
Verbatim2_Max_Size : constant Natural
:= Natural (Ada.Streams.Stream_Element'Last)
+ Verbatim1_Max_Size;
Input_Index : Positive := Input'First;
Length : Natural;
Word : Ada.Streams.Stream_Element;
procedure Find_Entry is
begin
Find_Entry
(Dict,
Input (Input_Index
.. Natural'Min (Input_Index + Dict.Max_Word_Length - 1,
Input'Last)),
Word,
Length);
end Find_Entry;
Previous_Verbatim_Beginning : Natural := 0;
Previous_Verbatim_Last : Ada.Streams.Stream_Element_Offset := 0;
begin
Output_Last := Output_Buffer'First - 1;
Find_Entry;
Main_Loop :
while Input_Index in Input'Range loop
Data_In_Dict :
while Length > 0 loop
Output_Last := Output_Last + 1;
Output_Buffer (Output_Last) := Word;
Input_Index := Input_Index + Length;
exit Main_Loop when Input_Index not in Input'Range;
Find_Entry;
end loop Data_In_Dict;
Verbatim_Block :
declare
Beginning : Positive := Input_Index;
Verbatim_Length, Block_Length : Natural;
begin
Verbatim_Scan :
while Length = 0 and Input_Index in Input'Range loop
Input_Index := Input_Index + 1;
Find_Entry;
end loop Verbatim_Scan;
Verbatim_Length := Input_Index - Beginning;
if Previous_Verbatim_Beginning > 0
and then Output_Last + Verbatim_Size (Dict, Verbatim_Length)
>= Previous_Verbatim_Last + Verbatim_Size
(Dict, Input_Index - Previous_Verbatim_Beginning)
then
Beginning := Previous_Verbatim_Beginning;
Output_Last := Previous_Verbatim_Last;
Verbatim_Length := Input_Index - Beginning;
else
Previous_Verbatim_Beginning := Beginning;
Previous_Verbatim_Last := Output_Last;
end if;
Verbatim_Encode :
while Verbatim_Length > 0 loop
if Dict.Variable_Length_Verbatim
and then Verbatim_Length > Verbatim1_Max_Size
then
Block_Length := Natural'Min
(Verbatim_Length, Verbatim2_Max_Size);
Output_Buffer (Output_Last + 1)
:= Ada.Streams.Stream_Element'Last;
Output_Buffer (Output_Last + 2) := Ada.Streams.Stream_Element
(Block_Length - Verbatim1_Max_Size);
Output_Last := Output_Last + 2;
else
Block_Length := Natural'Min
(Verbatim_Length, Verbatim1_Max_Size);
Output_Last := Output_Last + 1;
Output_Buffer (Output_Last)
:= Ada.Streams.Stream_Element'Last
- Ada.Streams.Stream_Element
(Block_Length - 1
+ Boolean'Pos (Dict.Variable_Length_Verbatim));
end if;
Verbatim_Copy :
for I in Beginning .. Beginning + Block_Length - 1 loop
Output_Last := Output_Last + 1;
Output_Buffer (Output_Last) := Character'Pos (Input (I));
end loop Verbatim_Copy;
Verbatim_Length := Verbatim_Length - Block_Length;
Beginning := Beginning + Block_Length;
end loop Verbatim_Encode;
end Verbatim_Block;
end loop Main_Loop;
end Compress;
function Compress (Dict : in Dictionary; Input : in String)
return Ada.Streams.Stream_Element_Array
is
Result : Ada.Streams.Stream_Element_Array
(1 .. Compressed_Upper_Bound (Dict, Input));
Last : Ada.Streams.Stream_Element_Offset;
begin
Compress (Dict, Input, Result, Last);
return Result (Result'First .. Last);
end Compress;
function Decompressed_Length
(Dict : in Dictionary;
Input : in Ada.Streams.Stream_Element_Array)
return Natural
is
Result : Natural := 0;
Verbatim_Code_Count : constant Ada.Streams.Stream_Element_Offset
:= Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Dict.Dict_Last);
Input_Index : Ada.Streams.Stream_Element_Offset := Input'First;
Input_Byte : Ada.Streams.Stream_Element;
Verbatim_Length : Ada.Streams.Stream_Element_Offset;
begin
while Input_Index in Input'Range loop
Input_Byte := Input (Input_Index);
if Input_Byte in Dict.Offsets'Range then
Result := Result + Dict_Entry (Dict, Input_Byte)'Length;
Input_Index := Input_Index + 1;
else
if not Dict.Variable_Length_Verbatim then
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Input_Byte) + 1;
elsif Input_Byte < Ada.Streams.Stream_Element'Last then
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Input_Byte);
else
Input_Index := Input_Index + 1;
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Input (Input_Index)) + Verbatim_Code_Count - 1;
end if;
Result := Result + Positive (Verbatim_Length);
Input_Index := Input_Index + Verbatim_Length + 1;
end if;
end loop;
return Result;
end Decompressed_Length;
procedure Decompress
(Dict : in Dictionary;
Input : in Ada.Streams.Stream_Element_Array;
Output_Buffer : out String;
Output_Last : out Natural)
is
procedure Append (S : in String);
procedure Append (S : in Ada.Streams.Stream_Element_Array);
procedure Append (S : in String) is
begin
Output_Buffer (Output_Last + 1 .. Output_Last + S'Length) := S;
Output_Last := Output_Last + S'Length;
end Append;
procedure Append (S : in Ada.Streams.Stream_Element_Array) is
begin
Append (To_String (S));
end Append;
Verbatim_Code_Count : constant Ada.Streams.Stream_Element_Offset
:= Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Dict.Dict_Last);
Input_Index : Ada.Streams.Stream_Element_Offset := Input'First;
Input_Byte : Ada.Streams.Stream_Element;
Verbatim_Length : Ada.Streams.Stream_Element_Offset;
begin
Output_Last := Output_Buffer'First - 1;
while Input_Index in Input'Range loop
Input_Byte := Input (Input_Index);
if Input_Byte in Dict.Offsets'Range then
Append (Dict_Entry (Dict, Input_Byte));
Input_Index := Input_Index + 1;
else
if not Dict.Variable_Length_Verbatim then
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Input_Byte) + 1;
elsif Input_Byte < Ada.Streams.Stream_Element'Last then
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Ada.Streams.Stream_Element'Last - Input_Byte);
else
Input_Index := Input_Index + 1;
Verbatim_Length := Ada.Streams.Stream_Element_Offset
(Input (Input_Index)) + Verbatim_Code_Count - 1;
end if;
Append (Input (Input_Index + 1 .. Input_Index + Verbatim_Length));
Input_Index := Input_Index + Verbatim_Length + 1;
end if;
end loop;
end Decompress;
function Decompress
(Dict : in Dictionary; Input : in Ada.Streams.Stream_Element_Array)
return String
is
Result : String (1 .. Decompressed_Length (Dict, Input));
Last : Natural;
begin
Decompress (Dict, Input, Result, Last);
pragma Assert (Last = Result'Last);
return Result;
end Decompress;
end Natools.Smaz;