Source file : zip-compress.ads
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-- Created 9-Dec-2007
-- This package facilitates the storage or compression of data.
-- Note that unlike decompression where the decoding is unique,
-- there is a quasi indefinite number of ways of compressing data into
-- most Zip-supported formats, including LZW (Shrink), Reduce, Deflate, or LZMA.
-- As a result, you may want to use your own way for compressing data.
-- This package is a portable one and doesn't claim to be the "best".
-- The term "best" is relative to the needs, since there are at least
-- two criteria that usually go in opposite directions: speed and
-- compression ratio, a bit like risk and return in finance.
package Zip.Compress is
-- Compression_Method is actually reflecting the way of compressing
-- data, not only the final compression format called "method" in
-- Zip specifications.
type Compression_Method is
(-- No compression:
-- Shrink = LZW algorithm, as in GIF pictures:
-- Reduce combines LZ and a Markov predictor; 4 strengths available:
-- Deflate combines LZ and Huffman encoding; 4 strengths available:
LZMA_3, -- NB: LZMA_3 can be very slow on large data
-- LZMA with non-default parameters, targeted for specific data types:
LZMA_for_ARW, -- Raw camera picture
LZMA_for_ORF, -- Raw camera picture
LZMA_for_PGM, -- TBD: photo vs drawing (expect much LZ redundancy in the latter)
LZMA_for_PPM, -- TBD: photo vs drawing (expect much LZ redundancy in the latter)
-- Preselection: select a method depending on hints, like the uncompressed size
Preselection_1, -- Not too slow; selects Deflate_3 or LZMA_2*
Preselection_2 -- Can be very slow on large data; selects Deflate_3, LZMA_2* or LZMA_3*
type Method_to_Format_type is array(Compression_Method) of PKZip_method;
Method_to_Format: constant Method_to_Format_type;
subtype Reduction_Method is Compression_Method range Reduce_1 .. Reduce_4;
-- Deflate_Fixed compresses the data into a single block and with predefined
-- ("fixed") compression structures. The data are basically LZ-compressed
-- only, since the Huffman code sets are flat and not tailored for the data.
subtype Deflation_Method is Compression_Method range Deflate_Fixed .. Deflate_3;
-- The multi-block Deflate methods use refined techniques to decide when to
-- start a new block and what sort of block to put next.
subtype Taillaule_Deflation_Method is Compression_Method range Deflate_1 .. Deflate_3;
subtype LZMA_Method is Compression_Method range LZMA_1 .. LZMA_for_WAV;
subtype Multi_Method is Compression_Method range Preselection_1 .. Preselection_2;
subtype Preselection_Method is Compression_Method range Preselection_1 .. Preselection_2;
subtype Single_Method is Compression_Method
range Compression_Method'First .. Compression_Method'Pred(Multi_Method'First);
type Data_content_type is (
ARW_RW2, -- Raw digital camera image
ORF_CR2, -- Raw digital camera image
GIF, PNG, PGM, PPM,
-- Compress data from an input stream to an output stream until
-- End_Of_File(input) = True, or number of input bytes = input_size .
-- If password /= "", an encryption header is written.
output : in out Zip_Streams.Root_Zipstream_Type'Class;
input_size : File_size_type; -- ignored if input_size_known = False
method : Compression_Method;
feedback : Feedback_proc;
password : String;
content_hint : Data_content_type;
CRC : out Interfaces.Unsigned_32;
output_size : out File_size_type;
zip_type : out Interfaces.Unsigned_16
-- ^ code corresponding to the compression method actually used
function Guess_type_from_name(name: String) return Data_content_type;
buffer_size: constant:= 1024 * 1024; -- 1 MB
Method_to_Format: constant Method_to_Format_type :=
(Store => store,
Shrink => shrink,
Reduce_1 => reduce_1,
Reduce_2 => reduce_2,
Reduce_3 => reduce_3,
Reduce_4 => reduce_4,
Deflation_Method => deflate,
LZMA_Method => lzma_meth,
Multi_Method => unknown
Zip-Ada: Ada library for zip archive files (.zip).
Some news about Zip-Ada and other related Ada projects
on Gautier's blog.