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crcmodel.h
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crcmodel.h
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/******************************************************************************/
/* */
/* Author : Ross Williams (ross@guest.adelaide.edu.au.). */
/* Date : 3 June 1993. */
/* Status : Public domain. */
/* */
/* Description : This is the header (.h) file for the reference */
/* implementation of the Rocksoft^tm Model CRC Algorithm. For more */
/* information on the Rocksoft^tm Model CRC Algorithm, see the document */
/* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */
/* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */
/* "ftp.adelaide.edu.au/pub/rocksoft". */
/* */
/* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */
/* */
/******************************************************************************/
/* */
/* How to Use This Package */
/* ----------------------- */
/* Step 1: Declare a variable of type cm_t. Declare another variable */
/* (p_cm say) of type p_cm_t and initialize it to point to the first */
/* variable (e.g. p_cm_t p_cm = &cm_t). */
/* */
/* Step 2: Assign values to the parameter fields of the structure. */
/* If you don't know what to assign, see the document cited earlier. */
/* For example: */
/* p_cm->cm_width = 16; */
/* p_cm->cm_poly = 0x8005L; */
/* p_cm->cm_init = 0L; */
/* p_cm->cm_refin = TRUE; */
/* p_cm->cm_refot = TRUE; */
/* p_cm->cm_xorot = 0L; */
/* Note: Poly is specified without its top bit (18005 becomes 8005). */
/* Note: Width is one bit less than the raw poly width. */
/* */
/* Step 3: Initialize the instance with a call cm_ini(p_cm); */
/* */
/* Step 4: Process zero or more message bytes by placing zero or more */
/* successive calls to cm_nxt. Example: cm_nxt(p_cm,ch); */
/* */
/* Step 5: Extract the CRC value at any time by calling crc = cm_crc(p_cm); */
/* If the CRC is a 16-bit value, it will be in the bottom 16 bits. */
/* */
/******************************************************************************/
/* */
/* Design Notes */
/* ------------ */
/* PORTABILITY: This package has been coded very conservatively so that */
/* it will run on as many machines as possible. For example, all external */
/* identifiers have been restricted to 6 characters and all internal ones to */
/* 8 characters. The prefix cm (for Crc Model) is used as an attempt to avoid */
/* namespace collisions. This package is endian independent. */
/* */
/* EFFICIENCY: This package (and its interface) is not designed for */
/* speed. The purpose of this package is to act as a well-defined reference */
/* model for the specification of CRC algorithms. If you want speed, cook up */
/* a specific table-driven implementation as described in the document cited */
/* above. This package is designed for validation only; if you have found or */
/* implemented a CRC algorithm and wish to describe it as a set of parameters */
/* to the Rocksoft^tm Model CRC Algorithm, your CRC algorithm implementation */
/* should behave identically to this package under those parameters. */
/* */
/******************************************************************************/
/* The following #ifndef encloses this entire */
/* header file, rendering it indempotent. */
#ifndef CM_DONE
#define CM_DONE
/******************************************************************************/
/* The following definitions are extracted from my style header file which */
/* would be cumbersome to distribute with this package. The DONE_STYLE is the */
/* idempotence symbol used in my style header file. */
#ifndef DONE_STYLE
typedef unsigned long ulong;
typedef unsigned bool;
typedef unsigned char *p_ubyte_;
#ifndef TRUE
#define FALSE 0
#define TRUE 1
#endif
/* Change to the second definition if you don't have prototypes. */
#define P_(A) A
/* #define P_(A) () */
/* Uncomment this definition if you don't have void. */
/* typedef int void; */
#endif
/******************************************************************************/
/* CRC Model Abstract Type */
/* ----------------------- */
/* The following type stores the context of an executing instance of the */
/* model algorithm. Most of the fields are model parameters which must be */
/* set before the first initializing call to cm_ini. */
typedef struct {
int cm_width; /* Parameter: Width in bits [8,32]. */
ulong cm_poly; /* Parameter: The algorithm's polynomial. */
ulong cm_init; /* Parameter: Initial register value. */
bool cm_refin; /* Parameter: Reflect input bytes? */
bool cm_refot; /* Parameter: Reflect output CRC? */
ulong cm_xorot; /* Parameter: XOR this to output CRC. */
ulong cm_reg; /* Context: Context during execution. */
} cm_t;
typedef cm_t *p_cm_t;
/******************************************************************************/
/* Functions That Implement The Model */
/* ---------------------------------- */
/* The following functions animate the cm_t abstraction. */
void cm_ini P_((p_cm_t p_cm));
/* Initializes the argument CRC model instance. */
/* All parameter fields must be set before calling this. */
void cm_nxt P_((p_cm_t p_cm, int ch));
/* Processes a single message byte [0,255]. */
void cm_blk P_((p_cm_t p_cm, p_ubyte_ blk_adr, ulong blk_len));
/* Processes a block of message bytes. */
ulong cm_crc P_((p_cm_t p_cm));
/* Returns the CRC value for the message bytes processed so far. */
/******************************************************************************/
/* Functions For Table Calculation */
/* ------------------------------- */
/* The following function can be used to calculate a CRC lookup table. */
/* It can also be used at run-time to create or check static tables. */
ulong cm_tab P_((p_cm_t p_cm, int index));
/* Returns the i'th entry for the lookup table for the specified algorithm. */
/* The function examines the fields cm_width, cm_poly, cm_refin, and the */
/* argument table index in the range [0,255] and returns the table entry in */
/* the bottom cm_width bytes of the return value. */
/******************************************************************************/
/* End of the header file idempotence #ifndef */
#endif