arith-code.h

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//  This file is part of MANTIS OS, Operating System
//  See http://mantis.cs.colorado.edu/
//
//  Copyright (C) 2003,2004,2005 University of Colorado, Boulder
//
//  This program is free software; you can redistribute it and/or
//  modify it under the terms of the mos license (see file LICENSE)

/** @file arith-code.h
 * @brief Symbol coding.
 *
 * largely based on: http://dogma.net/markn/articles/arith/
 */

/** @brief Max allowed frequency count. */
#define ARITH_CODE_MAXIMUM_SCALE   16383  
/** @brief Escape symbol. */
#define ARITH_CODE_ESCAPE          256  
/** @brief Output stream empty symbol. */
#define ARITH_CODE_DONE            -1    
/** @brief Symbol to flush the model. */
#define ARITH_CODE_FLUSH           -2   

/** @brief A symbol can be an int or a pair of counts on a scale.
   Here is the structure for the latter. */
typedef struct {
  /** @brief Overflow bits for start of code range.*/
   unsigned short int low_count; 
  /** @brief Overflow bits for end of code range. */
   unsigned short int high_count; 
  /** @brief Scale used */
   unsigned short int scale;
} arith_code_symbol_t;

/** @brief Encode a symbol
 * @param in_buf Input buffer
 * @param in_len Input length
 * @param out_buf Output buffer
 * @param out_len Output length
 */
void arith_code_encode (char *in_buf, uint8_t in_len,
			char *out_buf, uint8_t out_len);
/** @brief Decode a symbol
 * @param in_buf Input buffer
 * @param in_len Input length
 * @param out_buf Output buffer
 * @param out_len Output length
 */
void arith_code_decode (char *in_buf, uint8_t in_len,
			char *out_buf, uint8_t out_len);