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268 | -- LZMA library
----------------
-- Library for encoding and decoding data streams in the LZMA compression
-- format invented by Igor Pavlov.
--
-- Pure Ada 95+ code, 100% portable: OS-, CPU- and compiler- independent.
-- Legal licensing note:
-- Copyright (c) 2016 .. 2019 Gautier de Montmollin
-- SWITZERLAND
-- Permission is hereby granted, free of charge, to any person obtaining a copy
-- of this software and associated documentation files (the "Software"), to deal
-- in the Software without restriction, including without limitation the rights
-- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-- copies of the Software, and to permit persons to whom the Software is
-- furnished to do so, subject to the following conditions:
-- The above copyright notice and this permission notice shall be included in
-- all copies or substantial portions of the Software.
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-- THE SOFTWARE.
-- NB: this is the MIT License, as found 21-Aug-2016 on the site
-- http://www.opensource.org/licenses/mit-license.php
with Ada.Direct_IO; -- Only used for the type Data_Bytes_Count below.
with Interfaces;
with System;
package LZMA is
-- The compression and decompression procedures are located
-- in child packages LZMA.Encoding and LZMA.Decoding respectively.
-- Bits of last byte being used as context.
-- With the value 8, LZMA uses a complete Markov chain for predicting
-- a literal from the previous one, like PKZip's Reduce format.
subtype Literal_context_bits_range is Integer range 0 .. 8;
-- Position mod 2**bits is used, but for literal context only.
subtype Literal_position_bits_range is Integer range 0 .. 4;
-- Position mod 2**bits is used in various places.
subtype Position_bits_range is Integer range 0 .. 4;
Default_dictionary_size : constant := 2 ** 15; -- 32 KiB, like Deflate.
subtype Byte is Interfaces.Unsigned_8;
-- Ada.Direct_IO is only there for the Data_Bytes_Count type.
-- In case you want to avoid reference to Ada.Direct_IO,
-- you can customize the definition of Data_Bytes_Count, provided
-- it has enough capacity for counting bytes in the streams involved.
package BIO is new Ada.Direct_IO (Byte);
subtype Data_Bytes_Count is BIO.Count;
private
use Interfaces;
-- These integer types are defined in the LZMA specification
-- (DRAFT version, 2015-06-14, by Igor Pavlov)
type Unsigned is mod 2 ** System.Word_Size;
subtype UInt64 is Unsigned_64;
subtype UInt32 is Unsigned_32;
subtype UInt16 is Unsigned_16;
----------------------------
-- Finite state machine --
----------------------------
States_count : constant := 12; -- LZMA specification name: "kNumStates"
subtype State_range is Unsigned range 0 .. States_count - 1;
type Transition is array (State_range) of State_range;
------------------------------------ From ... 0 1 2 3 4 5 6 7 8 9 10 11
Update_State_Literal : constant Transition := (0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 4, 5);
Update_State_Match : constant Transition := (7, 7, 7, 7, 7, 7, 7, 10, 10, 10, 10, 10);
Update_State_Rep : constant Transition := (8, 8, 8, 8, 8, 8, 8, 11, 11, 11, 11, 11);
Update_State_ShortRep : constant Transition := (9, 9, 9, 9, 9, 9, 9, 11, 11, 11, 11, 11);
-- Context for improving compression of aligned data,
-- modulo 2**n = 2, 4, 8 or 16 (max) bytes, or disabled: n = 0.
Max_pos_bits : constant := 4; -- LZMA specification name: "kNumPosBitsMax"
Max_pos_states_count : constant := 2**Max_pos_bits;
subtype Pos_state_range is Unsigned range 0 .. Max_pos_states_count - 1;
----------------------------------------
-- Probability model for bit coding --
----------------------------------------
Probability_model_bits : constant := 11; -- LZMA specification name: "kNumBitModelTotalBits"
Probability_model_count : constant := 2 ** Probability_model_bits;
Probability_change_bits : constant := 5; -- LZMA specification name: "kNumMoveBits"
-- All probabilities are initialized with p=0.5. LZMA specification name: "PROB_INIT_VAL"
Initial_probability : constant := Probability_model_count / 2;
-- Type for storing probabilities, must have at least Probability_model_bits bits.
-- LZMA specification recommends UInt16. LzmaEnc.c uses UInt16 or optionally UInt32.
type CProb is new UInt16;
-- Integer (signed) used as index because there is a -1 (unused) index in Pos_coder_range.
type CProb_array is array (Integer range <>) of CProb;
Align_bits : constant := 4; -- LZMA specification name: "kNumAlignBits"
Align_table_size : constant := 2 ** Align_bits;
Align_mask : constant := Align_table_size - 1;
subtype Bits_3_range is Integer range 0 .. 2**3 - 1;
subtype Bits_6_range is Integer range 0 .. 2**6 - 1;
subtype Bits_8_range is Integer range 0 .. 2**8 - 1;
subtype Bits_NAB_range is Integer range 0 .. 2**Align_bits - 1;
subtype Probs_3_bits is CProb_array (Bits_3_range);
subtype Probs_6_bits is CProb_array (Bits_6_range);
subtype Probs_8_bits is CProb_array (Bits_8_range);
subtype Probs_NAB_bits is CProb_array (Bits_NAB_range);
--------------------------------------------------
-- Probabilities for the binary decision tree --
--------------------------------------------------
type Probs_state is array (State_range) of CProb;
type Probs_state_and_pos_state is array (State_range, Pos_state_range) of CProb;
type Probs_for_switches is record
-- This is the context for the switch between a Literal and a LZ Distance-Length code
match : Probs_state_and_pos_state := (others => (others => Initial_probability));
-- These are contexts for various repetition modes
rep : Probs_state := (others => Initial_probability);
rep_g0 : Probs_state := (others => Initial_probability);
rep_g1 : Probs_state := (others => Initial_probability);
rep_g2 : Probs_state := (others => Initial_probability);
rep0_long : Probs_state_and_pos_state := (others => (others => Initial_probability));
end record;
------------------------------------
-- Probabilities for LZ lengths --
------------------------------------
type Low_mid_coder_probs is array (Pos_state_range) of Probs_3_bits;
-- Probabilities used for encoding LZ lengths. LZMA specification name: "CLenDecoder"
type Probs_for_LZ_Lengths is record
choice_1 : CProb := Initial_probability; -- 0: low coder; 1: mid or high
choice_2 : CProb := Initial_probability; -- 0: mid; 1: high
low_coder : Low_mid_coder_probs := (others => (others => Initial_probability));
mid_coder : Low_mid_coder_probs := (others => (others => Initial_probability));
high_coder : Probs_8_bits := (others => Initial_probability);
end record;
--------------------------------------
-- Probabilities for LZ distances --
--------------------------------------
Len_to_pos_states : constant := 4;
subtype Slot_coder_range is Unsigned range 0 .. Len_to_pos_states - 1;
type Slot_coder_probs is array (Slot_coder_range) of Probs_6_bits;
Dist_slot_bits : constant := 6; -- "kNumPosSlotBits"
Start_dist_model_index : constant := 4; -- "kStartPosModelIndex"
End_dist_model_index : constant := 14; -- LZMA specification name: "kEndPosModelIndex"
Num_full_distances : constant := 2 ** (End_dist_model_index / 2); -- "kNumFullDistances"
-- Pos_coder_range: index -1 is never used as such but appears
-- when calling Bit_Tree_Reverse_Encode (as in the original C version, RcTree_ReverseEncode).
subtype Pos_coder_range is Integer range -1 .. Num_full_distances - End_dist_model_index;
subtype Pos_coder_probs is CProb_array (Pos_coder_range);
type Probs_for_LZ_Distances is record
slot_coder : Slot_coder_probs := (others => (others => Initial_probability));
align_coder : Probs_NAB_bits := (others => Initial_probability);
pos_coder : Pos_coder_probs := (others => Initial_probability);
end record;
--------------------------------------
-- All probabilities used by LZMA --
--------------------------------------
type All_probabilities (last_lit_prob_index : Integer) is record
-- Literals:
lit : CProb_array (0 .. last_lit_prob_index) := (others => Initial_probability);
-- Distances:
dist : Probs_for_LZ_Distances;
-- Lengths:
len : Probs_for_LZ_Lengths;
rep_len : Probs_for_LZ_Lengths;
-- Decision tree switches:
switch : Probs_for_switches;
end record;
-------------
-- Misc. --
-------------
-- Minimum dictionary (= plain text buffer of n previous bytes)
-- size is 4096. LZMA specification name: "LZMA_DIC_MIN"
Min_dictionary_size : constant := 2 ** 12;
-- Log2-style encoding of LZ lengths
Len_low_bits : constant := 3;
Len_low_symbols : constant := 2 ** Len_low_bits;
Len_mid_bits : constant := 3;
Len_mid_symbols : constant := 2 ** Len_mid_bits;
Len_high_bits : constant := 8;
Len_high_symbols : constant := 2 ** Len_high_bits;
Len_symbols : constant := Len_low_symbols + Len_mid_symbols + Len_high_symbols;
Min_match_length : constant := 2; -- "LZMA_MATCH_LEN_MIN"
Max_match_length : constant := Min_match_length + Len_symbols - 1; -- "LZMA_MATCH_LEN_MAX"
subtype Match_length_range is Integer range Min_match_length .. Max_match_length;
-- Fake distance, used as an end-of-stream marker.
end_of_stream_magic_distance : constant := 16#FFFF_FFFF#;
--------------------------------------------------
-- Binary values of various decision switches --
--------------------------------------------------
-- LZ literal vs. DL code
Literal_choice : constant := 0;
DL_code_choice : constant := 1;
-- Within DL code: "Simple match" vs. "Rep match"
Simple_match_choice : constant := 0;
Rep_match_choice : constant := 1;
-- Within "Rep match": "Distance is rep0" vs. "Distance is not rep0"
The_distance_is_rep0_choice : constant := 0;
The_distance_is_not_rep0_choice : constant := 1;
-- Within "Distance is rep0":
The_length_is_1_choice : constant := 0;
The_length_is_not_1_choice : constant := 1;
-- Within "Distance is not rep0": "Distance is rep1" vs. "Distance is not rep1"
The_distance_is_rep1_choice : constant := 0;
The_distance_is_not_rep1_choice : constant := 1;
-- Within "Distance is not rep1": "Distance is rep2" vs. "Distance is not rep2"
The_distance_is_rep2_choice : constant := 0;
The_distance_is_not_rep2_choice : constant := 1;
----------------------
-- Range encoding --
----------------------
-- Normalization threshold. When the range width is below that value,
-- a shift is needed.
width_threshold : constant := 2**24; -- LZMA specification name: "kTopValue"
-- The following article (the only reference in the LZMA specification)
-- explains how range encoding works:
--
-- G. N. N. Martin, Range encoding: an algorithm for removing redundancy
-- from a digitized message, Video & Data Recording Conference,
-- Southampton, UK, July 24-27, 1979.
end LZMA;
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