自适应压缩算法(Arithmetic Coding Library)

Arithmetic Coding Library ------------------------- Fred Wheeler Feb 24, 1996 This package was adapted from the program in "Arithmetic Coding for Data Compression", by Ian H. Witten, Radford M. Neal and John G. Cleary, Communications of the ACM, June 1987, Vol. 30, No. 6. (Source at ftp://ftp.cpsc.ucalgary.ca/pub/projects/ar.cod/cacm-87.shar) This version uses structures for the coder, decoder and data model instead of global variables. This object oriented approach allows you to simultaneously use several arithmetic coders, each streaming bits to a different file and to have several models for each coder, each with a possibly different number of symbols and frequency table. This package does not come with models for character, word and bit encoding, like the Witten Neal Cleary package. You must create your own model (probability table). Encoders can be given a file to which the bits are stored. If no file is given, the encoder will simply count the bits that would have been stored. Decoders must be given a file to work. Models may be initiated with a frequency table, or the table will default to uniform (all 1's). Regardless of initiation, the models can be adaptive or fixed. Unlike the original version by Witten et. al., symbol indices start at 0, not 1. The program is written in ANSI C. I owe credit to Amir Said, who has also written a similar package based on the Witten Neal Cleary package. If you find this program useful, please send me an e-mail. ACDEMO ------ The program ACDEMO is a simple demonstration of the multiple model arithmetic codec defined in ac.h and ac.c. ACDEMO encodes a few random streams and then decodes them, making sure that the original data is recovered. To be useful, ac.h and ac.c must be incorporated into another compression program. To compile and run ACDEMO with gcc use: gcc -Wall -O2 -c ac.c gcc -Wall -O2 -c acdemo.c gcc -o acdemo ac.o acdemo.o ./acdemo The most common problem encountered is the compiler not finding random() and srandom(), used in acdemo.c. See the comments in acdemo.c to fix this. Change Log ---------- Sep 10, 1999 by Fred Wheeler In ac.c removed declaration for main() and declarations for random functions. Jan 20, 1999 by Fred Wheeler In ac.c use "b" in fopen so files are opened in binary mode. This is necessary for the code to work on a PC. Jun 15, 2000 by Fred Wheeler Use macros for random/rand and srandom/srand and comment their usage Files ----- ac.c: source for all arithmetic coding functions ac.h: header file for any file using the arithmetic coding library acdemo.c: an example