00001 /******************************************************************************/ 00002 /* Start of crcmodel.h */ 00003 /******************************************************************************/ 00004 /* */ 00005 /* Author : Ross Williams (ross@guest.adelaide.edu.au.). */ 00006 /* Date : 3 June 1993. */ 00007 /* Status : Public domain. */ 00008 /* */ 00009 /* Description : This is the header (.h) file for the reference */ 00010 /* implementation of the Rocksoft^tm Model CRC Algorithm. For more */ 00011 /* information on the Rocksoft^tm Model CRC Algorithm, see the document */ 00012 /* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */ 00013 /* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */ 00014 /* "ftp.adelaide.edu.au/pub/rocksoft". */ 00015 /* */ 00016 /* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */ 00017 /* */ 00018 /******************************************************************************/ 00019 /* */ 00020 /* How to Use This Package */ 00021 /* ----------------------- */ 00022 /* Step 1: Declare a variable of type cm_t. Declare another variable */ 00023 /* (p_cm say) of type p_cm_t and initialize it to point to the first */ 00024 /* variable (e.g. p_cm_t p_cm = &cm_t). */ 00025 /* */ 00026 /* Step 2: Assign values to the parameter fields of the structure. */ 00027 /* If you don't know what to assign, see the document cited earlier. */ 00028 /* For example: */ 00029 /* p_cm->cm_width = 16; */ 00030 /* p_cm->cm_poly = 0x8005L; */ 00031 /* p_cm->cm_init = 0L; */ 00032 /* p_cm->cm_refin = TRUE; */ 00033 /* p_cm->cm_refot = TRUE; */ 00034 /* p_cm->cm_xorot = 0L; */ 00035 /* Note: Poly is specified without its top bit (18005 becomes 8005). */ 00036 /* Note: Width is one bit less than the raw poly width. */ 00037 /* */ 00038 /* Step 3: Initialize the instance with a call cm_ini(p_cm); */ 00039 /* */ 00040 /* Step 4: Process zero or more message bytes by placing zero or more */ 00041 /* successive calls to cm_nxt. Example: cm_nxt(p_cm,ch); */ 00042 /* */ 00043 /* Step 5: Extract the CRC value at any time by calling crc = cm_crc(p_cm); */ 00044 /* If the CRC is a 16-bit value, it will be in the bottom 16 bits. */ 00045 /* */ 00046 /******************************************************************************/ 00047 /* */ 00048 /* Design Notes */ 00049 /* ------------ */ 00050 /* PORTABILITY: This package has been coded very conservatively so that */ 00051 /* it will run on as many machines as possible. For example, all external */ 00052 /* identifiers have been restricted to 6 characters and all internal ones to */ 00053 /* 8 characters. The prefix cm (for Crc Model) is used as an attempt to avoid */ 00054 /* namespace collisions. This package is endian independent. */ 00055 /* */ 00056 /* EFFICIENCY: This package (and its interface) is not designed for */ 00057 /* speed. The purpose of this package is to act as a well-defined reference */ 00058 /* model for the specification of CRC algorithms. If you want speed, cook up */ 00059 /* a specific table-driven implementation as described in the document cited */ 00060 /* above. This package is designed for validation only; if you have found or */ 00061 /* implemented a CRC algorithm and wish to describe it as a set of parameters */ 00062 /* to the Rocksoft^tm Model CRC Algorithm, your CRC algorithm implementation */ 00063 /* should behave identically to this package under those parameters. */ 00064 /* */ 00065 /******************************************************************************/ 00066 00067 /* The following #ifndef encloses this entire */ 00068 /* header file, rendering it indempotent. */ 00069 #ifndef CM_DONE 00070 #define CM_DONE 00071 00072 /******************************************************************************/ 00073 00074 /* The following definitions are extracted from my style header file which */ 00075 /* would be cumbersome to distribute with this package. The DONE_STYLE is the */ 00076 /* idempotence symbol used in my style header file. */ 00077 00078 #ifndef DONE_STYLE 00079 00080 typedef unsigned long ulong; 00081 /*typedef unsigned bool; */ 00082 typedef unsigned char * p_ubyte_; 00083 00084 #ifndef TRUE 00085 #define FALSE 0 00086 #define TRUE 1 00087 #endif 00088 00089 /* Change to the second definition if you don't have prototypes. */ 00090 #define P_(A) A 00091 /* #define P_(A) () */ 00092 00093 /* Uncomment this definition if you don't have void. */ 00094 /* typedef int void; */ 00095 00096 #endif 00097 00098 /******************************************************************************/ 00099 00100 /* CRC Model Abstract Type */ 00101 /* ----------------------- */ 00102 /* The following type stores the context of an executing instance of the */ 00103 /* model algorithm. Most of the fields are model parameters which must be */ 00104 /* set before the first initializing call to cm_ini. */ 00105 00109 typedef struct 00110 { 00111 int cm_width; /* Parameter: Width in bits [8,32]. */ 00112 ulong cm_poly; /* Parameter: The algorithm's polynomial. */ 00113 ulong cm_init; /* Parameter: Initial register value. */ 00114 bool cm_refin; /* Parameter: Reflect input bytes? */ 00115 bool cm_refot; /* Parameter: Reflect output CRC? */ 00116 ulong cm_xorot; /* Parameter: XOR this to output CRC. */ 00117 00118 ulong cm_reg; /* Context: Context during execution. */ 00119 } cm_t; 00120 typedef cm_t *p_cm_t; 00121 00122 /******************************************************************************/ 00123 00124 /* Functions That Implement The Model */ 00125 /* ---------------------------------- */ 00126 /* The following functions animate the cm_t abstraction. */ 00127 00128 void cm_ini P_((p_cm_t p_cm)); 00129 /* Initializes the argument CRC model instance. */ 00130 /* All parameter fields must be set before calling this. */ 00131 00132 void cm_nxt P_((p_cm_t p_cm,int ch)); 00133 /* Processes a single message byte [0,255]. */ 00134 00135 void cm_blk P_((p_cm_t p_cm,p_ubyte_ blk_adr,ulong blk_len)); 00136 /* Processes a block of message bytes. */ 00137 00138 ulong cm_crc P_((p_cm_t p_cm)); 00139 /* Returns the CRC value for the message bytes processed so far. */ 00140 00141 /******************************************************************************/ 00142 00143 /* Functions For Table Calculation */ 00144 /* ------------------------------- */ 00145 /* The following function can be used to calculate a CRC lookup table. */ 00146 /* It can also be used at run-time to create or check static tables. */ 00147 00148 ulong cm_tab P_((p_cm_t p_cm,int index)); 00149 /* Returns the i'th entry for the lookup table for the specified algorithm. */ 00150 /* The function examines the fields cm_width, cm_poly, cm_refin, and the */ 00151 /* argument table index in the range [0,255] and returns the table entry in */ 00152 /* the bottom cm_width bytes of the return value. */ 00153 00154 /******************************************************************************/ 00155 00156 /* End of the header file idempotence #ifndef */ 00157 #endif 00158 00159 /******************************************************************************/ 00160 /* End of crcmodel.h */ 00161 /******************************************************************************/
1.3.7