-libaec - Adaptive Entropy Coding library
+**********************************************************************
+ libaec - Adaptive Entropy Coding library
+**********************************************************************
---------------------------------------------------------------------------------
-Copyright 2012
+libaec provides fast lossless compression of 1 up to 32 bit wide
+signed or unsigned integers. The library achieves best results for low
+entropy data as often encountered in space imaging instrument data or
+numerical model output from weather or climate simulations. While
+floating point representations are not directly supported, they can
+also be efficiently coded by grouping exponents and mantissa.
-Mathis Rosenhauer, Luis Kornblueh
-Moritz Hanke,
-Joerg Behrens
+libaec implements a Space Data System Standard [1], [2].
-Deutsches Klimarechenzentrum GmbH Max-Planck-Institut fuer Meteorologie
-Bundesstr. 45a Bundesstr. 53
-20146 Hamburg 20146 Hamburg
-Germany Germany
---------------------------------------------------------------------------------
-The implementation is based on:
+**********************************************************************
+ Patents
+**********************************************************************
-Consultative Committee for Space Data Systems. Lossless Data
+In doc/license.txt a clarification on potentially applying
+intellectual property rights is given.
+
+
+**********************************************************************
+ Installation
+**********************************************************************
+
+ See INSTALL for details.
+
+
+**********************************************************************
+ Encoding
+**********************************************************************
+
+In this context efficiency refers to the size of the encoded
+data. Performance refers to the time it takes to encode data.
+
+Suppose you have an array of 32 bit signed integers you want to
+compress. The pointer pointing to the data shall be called *source,
+output goes into *dest.
+
+#include <libaec.h>
+
+...
+ struct aec_stream strm;
+ int32_t *source;
+ unsigned char *dest;
+
+ /* input data ist 32 bits wide */
+ strm.bits_per_sample = 32;
+
+ /* define a block size of 16 */
+ strm.block_size = 16;
+
+ /* the reference sample interval is set to 128 blocks */
+ strm.rsi = 128;
+
+ /* input data is signed and needs to be preprocessed */
+ strm.flags = AEC_DATA_SIGNED | AEC_DATA_PREPROCESS;
+
+ /* pointer to input */
+ strm.next_in = (unsigned char *)source;
+
+ /* length of input in bytes */
+ strm.avail_in = source_length * 4;
+
+ /* pointer to output buffer */
+ strm.avail_out = dest;
+
+ /* length of output buffer in bytes */
+ strm.next_out = dest_lenth;
+
+ /* initialize encoding */
+ if (aec_encode_init(&strm) != AEC_OK)
+ return 1;
+
+ /* Perform encoding in one call and flush output. */
+ /* In this example you must be sure that the output */
+ /* buffer is large enough for all compressed output */
+ if (aec_encode(&strm, AEC_FLUSH) != AEC_OK)
+ return 1;
+
+ /* free all resources used by encoder */
+ aec_encode_end(&strm);
+...
+
+block_size can vary from 8 to 64. Smaller blocks allow the compression
+to adapt to rapid changes in entropy. Larger blocks create less
+overhead but can be less efficient.
+
+rsi sets the reference sample interval. A large RSI will improve
+performance and efficiency. It will also increase memory requiremens
+since internal buffering is based on RSI size. Smaller RSI may be
+desirable in situations where each RSI will be packetized and possible
+error propagation has to be minimized (e.g. on board a spacecraft[2]).
+
+Flags:
+
+AEC_DATA_SIGNED: input data are signed integers. Specifying this
+correctly increases compression efficiency. Default is unsigned.
+
+AEC_DATA_PREPROCESS: preprocessing input will almost always improve
+compression efficiency. It may only cost performance for no gain in
+efficiency if the data is already uncorrelated.
+
+AEC_DATA_MSB: input data is stored most significant byte first
+i.e. big endian. You have to specify AEC_DATA_MSB even if your host
+architecture is big endian. Default is little endian on all
+architectures.
+
+AEC_DATA_3BYTE: the 24 bit input data is stored in three bytes.
+
+Data size:
+
+Except for the AEC_DATA_3BYTE case for 24 bit data, the following
+rules apply:
+
+ data size storage size
+ 1 - 8 bit 1 byte
+ 9 - 16 bit 2 bytes
+17 - 32 bit 4 bytes (also for 24bit if AEC_DATA_3BYTE is not set)
+
+Flushing:
+
+aec_encode can be used in a streaming fashion by chunking input and
+output and specifying AEC_NO_FLUSH. The function will return if either
+the input runs empty or the output buffer is full. The calling
+function can check avail_in and avail_out to see what occcurred. aec.c
+is an example of streaming usage of encoding and decoding.
+
+
+**********************************************************************
+ Decoding
+**********************************************************************
+
+Usage for decoding is very similar to encoding, only the meaning of
+input and output is reversed.
+
+#include <libaec.h>
+
+...
+ struct aec_stream strm;
+ /* this is now the compressed data */
+ unsigned char *source;
+ /* here goes the uncompressed result */
+ int32_t *dest;
+
+ strm.bits_per_sample = 32;
+ strm.block_size = 16;
+ strm.rsi = 128;
+ strm.flags = AEC_DATA_SIGNED | AEC_DATA_PREPROCESS;
+ strm.next_in = source;
+ strm.avail_in = source_length;
+ strm.next_out = (unsigned char *)dest;
+ strm.avail_out = dest_lenth * 4;
+ if (aec_decode_init(&strm) != AEC_OK)
+ return 1;
+ if (aec_decode(&strm, AEC_FLUSH) != AEC_OK)
+ return 1;
+ aec_decode_end(&strm);
+...
+
+It is essential for decoding that parameters like bits_per_sample,
+block_size, rsi, and flags are exactly the same as they were for
+encoding. libaec does not store these parameters in the coded stream
+so it is up to the calling program to keep the correct parameters
+between encoding and decoding.
+
+
+**********************************************************************
+ References
+**********************************************************************
+
+[1] Consultative Committee for Space Data Systems. Lossless Data
Compression. Recommendation for Space Data System Standards, CCSDS
121.0-B-2. Blue Book. Issue 2. Washington, D.C.: CCSDS, May 2012.
-
http://public.ccsds.org/publications/archive/121x0b2.pdf
-Consultative Committee for Space Data Systems. Lossless Data
+[2] Consultative Committee for Space Data Systems. Lossless Data
Compression. Recommendation for Space Data System Standards, CCSDS
120.0-G-2. Green Book. Issue 2. Washington, D.C.: CCSDS, December
2006.
-
http://public.ccsds.org/publications/archive/120x0g2.pdf
-
-In doc/license.txt a clarification on potentially applying
-intellectual property rights is given.
projects / platform / upstream / libaec.git / commitdiff