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comparison Discovery/Src/crcmodel.c @ 38:5f11787b4f42

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author heinrichsweikamp
date Sat, 28 Apr 2018 11:52:34 +0200
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37:ccc45c0e1ea2 38:5f11787b4f42
1 /******************************************************************************/
2 /* Start of crcmodel.c */
3 /******************************************************************************/
4 /* */
5 /* Author : Ross Williams (ross@guest.adelaide.edu.au.). */
6 /* Date : 3 June 1993. */
7 /* Status : Public domain. */
8 /* */
9 /* Description : This is the implementation (.c) file for the reference */
10 /* implementation of the Rocksoft^tm Model CRC Algorithm. For more */
11 /* information on the Rocksoft^tm Model CRC Algorithm, see the document */
12 /* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */
13 /* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */
14 /* "ftp.adelaide.edu.au/pub/rocksoft". */
15 /* */
16 /* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */
17 /* */
18 /******************************************************************************/
19 /* */
20 /* Implementation Notes */
21 /* -------------------- */
22 /* To avoid inconsistencies, the specification of each function is not echoed */
23 /* here. See the header file for a description of these functions. */
24 /* This package is light on checking because I want to keep it short and */
25 /* simple and portable (i.e. it would be too messy to distribute my entire */
26 /* C culture (e.g. assertions package) with this package. */
27 /* */
28 /******************************************************************************/
29
30 #include "crcmodel.h"
31
32 /******************************************************************************/
33
34 /* The following definitions make the code more readable. */
35
36 #define BITMASK(X) (1L << (X))
37 #define MASK32 0xFFFFFFFFL
38 #define LOCAL static
39
40 /******************************************************************************/
41
42 LOCAL ulong reflect P_((ulong v,int b));
43 LOCAL ulong reflect (ulong v,int b)
44 /* Returns the value v with the bottom b [0,32] bits reflected. */
45 /* Example: reflect(0x3e23L,3) == 0x3e26 */
46 {
47 int i;
48 ulong t = v;
49 for (i=0; i<b; i++)
50 {
51 if (t & 1L)
52 v|= BITMASK((b-1)-i);
53 else
54 v&= ~BITMASK((b-1)-i);
55 t>>=1;
56 }
57 return v;
58 }
59
60 /******************************************************************************/
61
62 LOCAL ulong widmask P_((p_cm_t));
63 LOCAL ulong widmask (p_cm_t p_cm)
64 /* Returns a longword whose value is (2^p_cm->cm_width)-1. */
65 /* The trick is to do this portably (e.g. without doing <<32). */
66 {
67 return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L;
68 }
69
70 /******************************************************************************/
71
72 void cm_ini (p_cm_t p_cm)
73 {
74 p_cm->cm_reg = p_cm->cm_init;
75 }
76
77 /******************************************************************************/
78
79 void cm_nxt (p_cm_t p_cm, int ch)
80 {
81 int i;
82 ulong uch = (ulong) ch;
83 ulong topbit = BITMASK(p_cm->cm_width-1);
84
85 if (p_cm->cm_refin) uch = reflect(uch,8);
86 p_cm->cm_reg ^= (uch << (p_cm->cm_width-8));
87 for (i=0; i<8; i++)
88 {
89 if (p_cm->cm_reg & topbit)
90 p_cm->cm_reg = (p_cm->cm_reg << 1) ^ p_cm->cm_poly;
91 else
92 p_cm->cm_reg <<= 1;
93 p_cm->cm_reg &= widmask(p_cm);
94 }
95 }
96
97 /******************************************************************************/
98
99 void cm_blk (p_cm_t p_cm,p_ubyte_ blk_adr,ulong blk_len)
100 {
101 while (blk_len--) cm_nxt(p_cm,*blk_adr++);
102 }
103
104 /******************************************************************************/
105
106 ulong cm_crc (p_cm_t p_cm)
107 {
108 if (p_cm->cm_refot)
109 return p_cm->cm_xorot ^ reflect(p_cm->cm_reg,p_cm->cm_width);
110 else
111 return p_cm->cm_xorot ^ p_cm->cm_reg;
112 }
113
114 /******************************************************************************/
115
116 ulong cm_tab (p_cm_t p_cm, int index)
117 {
118 int i;
119 ulong r;
120 ulong topbit = BITMASK(p_cm->cm_width-1);
121 ulong inbyte = (ulong) index;
122
123 if (p_cm->cm_refin) inbyte = reflect(inbyte,8);
124 r = inbyte << (p_cm->cm_width-8);
125 for (i=0; i<8; i++)
126 if (r & topbit)
127 r = (r << 1) ^ p_cm->cm_poly;
128 else
129 r<<=1;
130 if (p_cm->cm_refin) r = reflect(r,p_cm->cm_width);
131 return r & widmask(p_cm);
132 }
133
134 /******************************************************************************/
135 /* End of crcmodel.c */
136 /******************************************************************************/
137