« back to all changes in this revision
Viewing changes to prbsgen.h
- browse files at revision 1
- compare with another revision
- compare with revision 1
- download diff
- download tarball
- view history from revision 1
- Committer: Bazaar Package Importer
- Author(s): Free Ekanayaka
- Date: 2007-05-14 22:18:54 UTC
- Revision ID: james.westby@ubuntu.com-20070514221854-274rj6fqs5tegu7q
Tags: upstream-0.6.6+2
Import upstream version 0.6.6+2
- files added:
added
removed
prbsgen.h
1
/*
2
Copyright (C) 2003 Fons Adriaensen <fons.adriaensen@skynet.be>
3
4
This program is free software; you can redistribute it and/or modify
5
it under the terms of the GNU General Public License as published by
6
the Free Software Foundation; either version 2 of the License, or
7
(at your option) any later version.
8
9
This program is distributed in the hope that it will be useful,
10
but WITHOUT ANY WARRANTY; without even the implied warranty of
11
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12
GNU General Public License for more details.
13
14
You should have received a copy of the GNU General Public License
15
along with this program; if not, write to the Free Software
16
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17
*/
18
19
20
#ifndef __PRBSGEN_H
21
#define __PRBSGEN_H
22
23
24
#include <assert.h>
25
#include "itypes.h"
26
27
28
//---------------------------------------------------------------------------
29
//
30
// Class Synopsis: class Prbs_gen
31
//
32
// Description:
33
// Pseudo random binary sequence generator using polynomial
34
// division in GF (2).
35
//
36
// There are two ways to built such a generator. Both use some
37
// form of shift register.
38
//
39
// 1. The first type feeds back the parity (XOR) of the taps corresponding to
40
// the non-zero elements of the polynomial into the input of the register.
41
// This is the most efficient way to do it in hardware.
42
//
43
// 2. In the seond form, when the bit shifted out is 1, the contents of the
44
// register are XORed with a bit pattern representing the polynomial.
45
// This is the best way to do it in software.
46
//
47
// Mutatis mutandis the two forms are equivalent. Any sequence that can be
48
// generated by one of the realisations can also be produced by the other.
49
// This software obviously uses the second form. It can use any polynomial
50
// up to (and including) a degree of 32.
51
//
52
//
53
// set_poly (p)
54
//
55
// Defines the polynomial to be used. The value of p is found from the
56
// sequence of coefficients (0 or 1) of the polynomial starting with the
57
// constant term, and dropping the highest one
58
//
59
// 0 1 2 3 4 5 6 7
60
// Example: P = x^7 + x^6 + 1 --> 1 0 0 0 0 0 1 1 --> 1000001 --> 0x41
61
//
62
// To emulate the first form described above, start with the highest
63
// exponent and drop the constant term.
64
//
65
// 7 6 5 4 3 2 1 0
66
// Example: P = x^7 + x^6 + 1 --> 1 1 0 0 0 0 0 1 --> 1100000 --> 0x60
67
//
68
// Also sets the state to all ones.
69
//
70
//
71
// set_state (x)
72
//
73
// Sets the initial state to x.
74
//
75
//
76
// step ()
77
//
78
// Returns the next pseudo random bit.
79
//
80
//
81
// sync_forw (x)
82
//
83
// This sets the generator in a state as if the last N (= degree) bits
84
// were those defined by x (the LSB of x represents the oldest bit).
85
// This can be used to synchronise a BER counter to a received bit stream,
86
// or to set the initial state when emulating a generator of the first form
87
// when the output is taken from the feedback.
88
//
89
//
90
// sync_back (x)
91
//
92
// This sets the generator in a state so that the first N (= degree) output
93
// bits will be those defined by x (the LSB of x will be the first output bit).
94
// This can be used to set the initial state when emulating a generator of
95
// the first form when the output is taken from the shifted out bit.
96
//
97
//
98
//---------------------------------------------------------------------------==
99
100
101
class Prbsgen
102
{
103
public:
104
105
enum
106
{
107
// Some polynomials for maximum length seqeunces.
108
109
G7 = 0x00000041,
110
G8 = 0x0000008E,
111
G15 = 0x00004001,
112
G16 = 0x00008016,
113
G23 = 0x00400010,
114
G24 = 0x0080000D,
115
G31 = 0x40000004,
116
G32 = 0x80000057,
117
};
118
119
Prbsgen (void);
120
121
void set_poly (U32 poly);
122
void set_stat (U32 stat);
123
void sync_forw (U32 bits);
124
void sync_back (U32 bits);
125
int step (void);
126
void crc_in (int b);
127
int crc_out (void);
128
129
U32 stat (void) const;
130
U32 poly (void) const;
131
U32 mask (void) const;
132
U32 hbit (void) const;
133
int degr (void) const;
134
135
~Prbsgen (void);
136
137
private:
138
139
U32 _stat;
140
U32 _poly;
141
U32 _mask;
142
U32 _hbit;
143
int _degr;
144
145
};
146
147
148
inline Prbsgen::Prbsgen (void)
149
: _stat (0), _poly (0), _mask (0), _degr (0)
150
{
151
}
152
153
154
inline Prbsgen::~Prbsgen (void)
155
{
156
}
157
158
159
inline void Prbsgen::set_poly (U32 poly)
160
{
161
assert (poly != 0);
162
163
_poly = poly;
164
_mask = 0;
165
_degr = 0;
166
167
while (_mask < _poly)
168
{
169
_mask = (_mask << 1) | 1;
170
_degr += 1;
171
}
172
_stat = _mask;
173
_hbit = (_mask >> 1) + 1;
174
}
175
176
177
inline void Prbsgen::set_stat (U32 stat)
178
{
179
assert (_poly != 0);
180
181
_stat = stat & _mask;
182
183
assert (_stat != 0);
184
}
185
186
187
inline int Prbsgen::step (void)
188
{
189
int bit;
190
191
assert (_poly != 0);
192
193
bit = _stat & 1;
194
_stat >>= 1;
195
if (bit) _stat ^= _poly;
196
197
return bit;
198
}
199
200
201
inline void Prbsgen::sync_forw (U32 bits)
202
{
203
assert (_poly != 0);
204
205
for (int i = 0; i < _degr; i++)
206
{
207
_stat >>= 1;
208
if (bits & 1) _stat ^= _poly;
209
bits >>= 1;
210
}
211
}
212
213
214
inline void Prbsgen::sync_back (U32 bits)
215
{
216
assert (_poly != 0);
217
218
_stat = 0;
219
for (int h = _hbit; h; h >>= 1)
220
{
221
if (bits & h) _stat ^= _poly;
222
_stat <<= 1;
223
}
224
_stat ^= bits;
225
_stat &= _mask;
226
}
227
228
229
inline void Prbsgen::crc_in (int b)
230
{
231
int bit;
232
233
assert (_poly != 0);
234
235
bit = (_stat & 1) ^ b;
236
_stat >>= 1;
237
if (bit) _stat ^= _poly;
238
}
239
240
241
inline int Prbsgen::crc_out (void)
242
{
243
int bit;
244
245
assert (_poly != 0);
246
247
bit = (_stat & 1);
248
_stat >>= 1;
249
return bit;
250
}
251
252
253
inline U32 Prbsgen::stat (void) const { return _stat; }
254
255
inline U32 Prbsgen::poly (void) const { return _poly; }
256
257
inline U32 Prbsgen::mask (void) const { return _mask; }
258
259
inline U32 Prbsgen::hbit (void) const { return _hbit; }
260
261
inline int Prbsgen::degr (void) const { return _degr; }
262
263
264
#endif
Loggerhead is a web-based interface for Breezy
Version: 2.0.1