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