annotate Discovery/Src/crcmodel.c @ 199:ac58a9fb92ac div-fixes-cleaup-2

Bugfix: fix initial CNS data in the logbook header Apparently, there has been confusion in the past about the data format of the CNS data in the logbook. This seems to be partially fixed back in 2015, but this fix forgot that the initial CNS data is also in the logbook header. So, now, the logbook header also stores the initial CNS data in a correct way, which fixes the problem of strange CNS values at the very start of repetitive dives, that get reset in the dive profile after the first CNS sample data comes along. Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>
author Jan Mulder <jlmulder@xs4all.nl>
date Fri, 22 Mar 2019 08:36:39 +0100
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38
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1 /******************************************************************************/
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2 /* Start of crcmodel.c */
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3 /******************************************************************************/
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4 /* */
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5 /* Author : Ross Williams (ross@guest.adelaide.edu.au.). */
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6 /* Date : 3 June 1993. */
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7 /* Status : Public domain. */
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8 /* */
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9 /* Description : This is the implementation (.c) file for the reference */
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10 /* implementation of the Rocksoft^tm Model CRC Algorithm. For more */
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11 /* information on the Rocksoft^tm Model CRC Algorithm, see the document */
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12 /* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */
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13 /* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */
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14 /* "ftp.adelaide.edu.au/pub/rocksoft". */
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15 /* */
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16 /* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */
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17 /* */
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18 /******************************************************************************/
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19 /* */
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20 /* Implementation Notes */
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21 /* -------------------- */
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22 /* To avoid inconsistencies, the specification of each function is not echoed */
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23 /* here. See the header file for a description of these functions. */
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24 /* This package is light on checking because I want to keep it short and */
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25 /* simple and portable (i.e. it would be too messy to distribute my entire */
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26 /* C culture (e.g. assertions package) with this package. */
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27 /* */
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28 /******************************************************************************/
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29
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30 #include "crcmodel.h"
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31
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32 /******************************************************************************/
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33
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34 /* The following definitions make the code more readable. */
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35
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36 #define BITMASK(X) (1L << (X))
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37 #define MASK32 0xFFFFFFFFL
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38 #define LOCAL static
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39
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40 /******************************************************************************/
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41
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42 LOCAL ulong reflect P_((ulong v,int b));
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43 LOCAL ulong reflect (ulong v,int b)
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44 /* Returns the value v with the bottom b [0,32] bits reflected. */
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45 /* Example: reflect(0x3e23L,3) == 0x3e26 */
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46 {
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47 int i;
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48 ulong t = v;
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49 for (i=0; i<b; i++)
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50 {
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51 if (t & 1L)
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52 v|= BITMASK((b-1)-i);
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53 else
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54 v&= ~BITMASK((b-1)-i);
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55 t>>=1;
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56 }
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57 return v;
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58 }
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59
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60 /******************************************************************************/
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61
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62 LOCAL ulong widmask P_((p_cm_t));
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63 LOCAL ulong widmask (p_cm_t p_cm)
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64 /* Returns a longword whose value is (2^p_cm->cm_width)-1. */
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65 /* The trick is to do this portably (e.g. without doing <<32). */
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66 {
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67 return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L;
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68 }
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69
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70 /******************************************************************************/
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71
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72 void cm_ini (p_cm_t p_cm)
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73 {
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74 p_cm->cm_reg = p_cm->cm_init;
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75 }
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76
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77 /******************************************************************************/
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78
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79 void cm_nxt (p_cm_t p_cm, int ch)
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80 {
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81 int i;
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82 ulong uch = (ulong) ch;
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83 ulong topbit = BITMASK(p_cm->cm_width-1);
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84
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85 if (p_cm->cm_refin) uch = reflect(uch,8);
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86 p_cm->cm_reg ^= (uch << (p_cm->cm_width-8));
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87 for (i=0; i<8; i++)
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88 {
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89 if (p_cm->cm_reg & topbit)
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90 p_cm->cm_reg = (p_cm->cm_reg << 1) ^ p_cm->cm_poly;
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91 else
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92 p_cm->cm_reg <<= 1;
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93 p_cm->cm_reg &= widmask(p_cm);
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94 }
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95 }
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96
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97 /******************************************************************************/
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98
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99 void cm_blk (p_cm_t p_cm,p_ubyte_ blk_adr,ulong blk_len)
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100 {
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101 while (blk_len--) cm_nxt(p_cm,*blk_adr++);
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102 }
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103
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104 /******************************************************************************/
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105
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106 ulong cm_crc (p_cm_t p_cm)
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107 {
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108 if (p_cm->cm_refot)
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109 return p_cm->cm_xorot ^ reflect(p_cm->cm_reg,p_cm->cm_width);
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110 else
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111 return p_cm->cm_xorot ^ p_cm->cm_reg;
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112 }
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113
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114 /******************************************************************************/
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115
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116 ulong cm_tab (p_cm_t p_cm, int index)
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117 {
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118 int i;
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119 ulong r;
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120 ulong topbit = BITMASK(p_cm->cm_width-1);
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121 ulong inbyte = (ulong) index;
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122
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123 if (p_cm->cm_refin) inbyte = reflect(inbyte,8);
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124 r = inbyte << (p_cm->cm_width-8);
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125 for (i=0; i<8; i++)
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126 if (r & topbit)
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127 r = (r << 1) ^ p_cm->cm_poly;
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128 else
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129 r<<=1;
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130 if (p_cm->cm_refin) r = reflect(r,p_cm->cm_width);
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131 return r & widmask(p_cm);
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132 }
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133
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134 /******************************************************************************/
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135 /* End of crcmodel.c */
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136 /******************************************************************************/
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137