161
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1 /******************************************************************************/
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2 /* */
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3 /* Author : Ross Williams (ross@guest.adelaide.edu.au.). */
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4 /* Date : 3 June 1993. */
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5 /* Status : Public domain. */
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6 /* */
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7 /* Description : This is the header (.h) file for the reference */
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8 /* implementation of the Rocksoft^tm Model CRC Algorithm. For more */
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9 /* information on the Rocksoft^tm Model CRC Algorithm, see the document */
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10 /* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */
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11 /* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */
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12 /* "ftp.adelaide.edu.au/pub/rocksoft". */
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13 /* */
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14 /* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */
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15 /* */
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16 /******************************************************************************/
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17 /* */
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18 /* How to Use This Package */
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19 /* ----------------------- */
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20 /* Step 1: Declare a variable of type cm_t. Declare another variable */
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21 /* (p_cm say) of type p_cm_t and initialize it to point to the first */
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22 /* variable (e.g. p_cm_t p_cm = &cm_t). */
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23 /* */
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24 /* Step 2: Assign values to the parameter fields of the structure. */
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25 /* If you don't know what to assign, see the document cited earlier. */
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26 /* For example: */
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27 /* p_cm->cm_width = 16; */
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28 /* p_cm->cm_poly = 0x8005L; */
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29 /* p_cm->cm_init = 0L; */
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30 /* p_cm->cm_refin = TRUE; */
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31 /* p_cm->cm_refot = TRUE; */
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32 /* p_cm->cm_xorot = 0L; */
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33 /* Note: Poly is specified without its top bit (18005 becomes 8005). */
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34 /* Note: Width is one bit less than the raw poly width. */
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35 /* */
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36 /* Step 3: Initialize the instance with a call cm_ini(p_cm); */
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37 /* */
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38 /* Step 4: Process zero or more message bytes by placing zero or more */
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39 /* successive calls to cm_nxt. Example: cm_nxt(p_cm,ch); */
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40 /* */
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41 /* Step 5: Extract the CRC value at any time by calling crc = cm_crc(p_cm); */
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42 /* If the CRC is a 16-bit value, it will be in the bottom 16 bits. */
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43 /* */
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44 /******************************************************************************/
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45 /* */
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46 /* Design Notes */
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47 /* ------------ */
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48 /* PORTABILITY: This package has been coded very conservatively so that */
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49 /* it will run on as many machines as possible. For example, all external */
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50 /* identifiers have been restricted to 6 characters and all internal ones to */
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51 /* 8 characters. The prefix cm (for Crc Model) is used as an attempt to avoid */
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52 /* namespace collisions. This package is endian independent. */
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53 /* */
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54 /* EFFICIENCY: This package (and its interface) is not designed for */
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55 /* speed. The purpose of this package is to act as a well-defined reference */
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56 /* model for the specification of CRC algorithms. If you want speed, cook up */
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57 /* a specific table-driven implementation as described in the document cited */
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58 /* above. This package is designed for validation only; if you have found or */
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59 /* implemented a CRC algorithm and wish to describe it as a set of parameters */
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60 /* to the Rocksoft^tm Model CRC Algorithm, your CRC algorithm implementation */
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61 /* should behave identically to this package under those parameters. */
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62 /* */
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63 /******************************************************************************/
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64
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65 /* The following #ifndef encloses this entire */
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66 /* header file, rendering it indempotent. */
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67 #ifndef CM_DONE
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68 #define CM_DONE
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69
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70 /******************************************************************************/
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71
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72 /* The following definitions are extracted from my style header file which */
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73 /* would be cumbersome to distribute with this package. The DONE_STYLE is the */
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74 /* idempotence symbol used in my style header file. */
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75
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76 #ifndef DONE_STYLE
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77
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78 typedef unsigned long ulong;
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79 typedef unsigned bool;
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80 typedef unsigned char *p_ubyte_;
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81
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82 #ifndef TRUE
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83 #define FALSE 0
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84 #define TRUE 1
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85 #endif
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86
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87 /* Change to the second definition if you don't have prototypes. */
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88 #define P_(A) A
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89 /* #define P_(A) () */
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90
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91 /* Uncomment this definition if you don't have void. */
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92 /* typedef int void; */
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93
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94 #endif
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95
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96 /******************************************************************************/
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97
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98 /* CRC Model Abstract Type */
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99 /* ----------------------- */
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100 /* The following type stores the context of an executing instance of the */
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101 /* model algorithm. Most of the fields are model parameters which must be */
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102 /* set before the first initializing call to cm_ini. */
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103 typedef struct {
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104 int cm_width; /* Parameter: Width in bits [8,32]. */
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105 ulong cm_poly; /* Parameter: The algorithm's polynomial. */
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106 ulong cm_init; /* Parameter: Initial register value. */
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107 bool cm_refin; /* Parameter: Reflect input bytes? */
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108 bool cm_refot; /* Parameter: Reflect output CRC? */
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109 ulong cm_xorot; /* Parameter: XOR this to output CRC. */
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110
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111 ulong cm_reg; /* Context: Context during execution. */
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112 } cm_t;
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113 typedef cm_t *p_cm_t;
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114
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115 /******************************************************************************/
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116
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117 /* Functions That Implement The Model */
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118 /* ---------------------------------- */
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119 /* The following functions animate the cm_t abstraction. */
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120
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121 void cm_ini P_((p_cm_t p_cm));
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122 /* Initializes the argument CRC model instance. */
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123 /* All parameter fields must be set before calling this. */
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124
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125 void cm_nxt P_((p_cm_t p_cm, int ch));
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126 /* Processes a single message byte [0,255]. */
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127
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128 void cm_blk P_((p_cm_t p_cm, p_ubyte_ blk_adr, ulong blk_len));
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129 /* Processes a block of message bytes. */
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130
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131 ulong cm_crc P_((p_cm_t p_cm));
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132 /* Returns the CRC value for the message bytes processed so far. */
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133
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134 /******************************************************************************/
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135
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136 /* Functions For Table Calculation */
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137 /* ------------------------------- */
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138 /* The following function can be used to calculate a CRC lookup table. */
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139 /* It can also be used at run-time to create or check static tables. */
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140
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141 ulong cm_tab P_((p_cm_t p_cm, int index));
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142 /* Returns the i'th entry for the lookup table for the specified algorithm. */
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143 /* The function examines the fields cm_width, cm_poly, cm_refin, and the */
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144 /* argument table index in the range [0,255] and returns the table entry in */
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145 /* the bottom cm_width bytes of the return value. */
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146
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147 /******************************************************************************/
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148
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149 /* End of the header file idempotence #ifndef */
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150 #endif
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