summaryrefslogtreecommitdiffstats
path: root/lib/reed_solomon/reed_solomon.c
blob: f5fef948a415e0cb3118b0a22eaab4f374e044b3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
/*
 * lib/reed_solomon/rslib.c
 *
 * Overview:
 *   Generic Reed Solomon encoder / decoder library
 *
 * Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
 *
 * Reed Solomon code lifted from reed solomon library written by Phil Karn
 * Copyright 2002 Phil Karn, KA9Q
 *
 * $Id: rslib.c,v 1.7 2005/11/07 11:14:59 gleixner Exp $
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Description:
 *
 * The generic Reed Solomon library provides runtime configurable
 * encoding / decoding of RS codes.
 * Each user must call init_rs to get a pointer to a rs_control
 * structure for the given rs parameters. This structure is either
 * generated or a already available matching control structure is used.
 * If a structure is generated then the polynomial arrays for
 * fast encoding / decoding are built. This can take some time so
 * make sure not to call this function from a time critical path.
 * Usually a module / driver should initialize the necessary
 * rs_control structure on module / driver init and release it
 * on exit.
 * The encoding puts the calculated syndrome into a given syndrome
 * buffer.
 * The decoding is a two step process. The first step calculates
 * the syndrome over the received (data + syndrome) and calls the
 * second stage, which does the decoding / error correction itself.
 * Many hw encoders provide a syndrome calculation over the received
 * data + syndrome and can call the second stage directly.
 *
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/rslib.h>
#include <linux/slab.h>
#include <asm/semaphore.h>

/* This list holds all currently allocated rs control structures */
static LIST_HEAD (rslist);
/* Protection for the list */
static DECLARE_MUTEX(rslistlock);

/**
 * rs_init - Initialize a Reed-Solomon codec
 *
 * @symsize:	symbol size, bits (1-8)
 * @gfpoly:	Field generator polynomial coefficients
 * @fcr:	first root of RS code generator polynomial, index form
 * @prim:	primitive element to generate polynomial roots
 * @nroots:	RS code generator polynomial degree (number of roots)
 *
 * Allocate a control structure and the polynom arrays for faster
 * en/decoding. Fill the arrays according to the given parameters
 */
static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
				   int prim, int nroots)
{
	struct rs_control *rs;
	int i, j, sr, root, iprim;

	/* Allocate the control structure */
	rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL);
	if (rs == NULL)
		return NULL;

	INIT_LIST_HEAD(&rs->list);

	rs->mm = symsize;
	rs->nn = (1 << symsize) - 1;
	rs->fcr = fcr;
	rs->prim = prim;
	rs->nroots = nroots;
	rs->gfpoly = gfpoly;

	/* Allocate the arrays */
	rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
	if (rs->alpha_to == NULL)
		goto errrs;

	rs->index_of = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
	if (rs->index_of == NULL)
		goto erralp;

	rs->genpoly = kmalloc(sizeof(uint16_t) * (rs->nroots + 1), GFP_KERNEL);
	if(rs->genpoly == NULL)
		goto erridx;

	/* Generate Galois field lookup tables */
	rs->index_of[0] = rs->nn;	/* log(zero) = -inf */
	rs->alpha_to[rs->nn] = 0;	/* alpha**-inf = 0 */
	sr = 1;
	for (i = 0; i < rs->nn; i++) {
		rs->index_of[sr] = i;
		rs->alpha_to[i] = sr;
		sr <<= 1;
		if (sr & (1 << symsize))
			sr ^= gfpoly;
		sr &= rs->nn;
	}
	/* If it's not primitive, exit */
	if(sr != 1)
		goto errpol;

	/* Find prim-th root of 1, used in decoding */
	for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
	/* prim-th root of 1, index form */
	rs->iprim = iprim / prim;

	/* Form RS code generator polynomial from its roots */
	rs->genpoly[0] = 1;
	for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
		rs->genpoly[i + 1] = 1;
		/* Multiply rs->genpoly[] by  @**(root + x) */
		for (j = i; j > 0; j--) {
			if (rs->genpoly[j] != 0) {
				rs->genpoly[j] = rs->genpoly[j -1] ^
					rs->alpha_to[rs_modnn(rs,
					rs->index_of[rs->genpoly[j]] + root)];
			} else
				rs->genpoly[j] = rs->genpoly[j - 1];
		}
		/* rs->genpoly[0] can never be zero */
		rs->genpoly[0] =
			rs->alpha_to[rs_modnn(rs,
				rs->index_of[rs->genpoly[0]] + root)];
	}
	/* convert rs->genpoly[] to index form for quicker encoding */
	for (i = 0; i <= nroots; i++)
		rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
	return rs;

	/* Error exit */
errpol:
	kfree(rs->genpoly);
erridx:
	kfree(rs->index_of);
erralp:
	kfree(rs->alpha_to);
errrs:
	kfree(rs);
	return NULL;
}


/**
 *  free_rs - Free the rs control structure, if its not longer used
 *
 *  @rs:	the control structure which is not longer used by the
 *		caller
 */
void free_rs(struct rs_control *rs)
{
	down(&rslistlock);
	rs->users--;
	if(!rs->users) {
		list_del(&rs->list);
		kfree(rs->alpha_to);
		kfree(rs->index_of);
		kfree(rs->genpoly);
		kfree(rs);
	}
	up(&rslistlock);
}

/**
 * init_rs - Find a matching or allocate a new rs control structure
 *
 *  @symsize:	the symbol size (number of bits)
 *  @gfpoly:	the extended Galois field generator polynomial coefficients,
 *		with the 0th coefficient in the low order bit. The polynomial
 *		must be primitive;
 *  @fcr:  	the first consecutive root of the rs code generator polynomial
 *		in index form
 *  @prim:	primitive element to generate polynomial roots
 *  @nroots:	RS code generator polynomial degree (number of roots)
 */
struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
			   int nroots)
{
	struct list_head	*tmp;
	struct rs_control	*rs;

	/* Sanity checks */
	if (symsize < 1)
		return NULL;
	if (fcr < 0 || fcr >= (1<<symsize))
    		return NULL;
	if (prim <= 0 || prim >= (1<<symsize))
    		return NULL;
	if (nroots < 0 || nroots >= (1<<symsize))
		return NULL;

	down(&rslistlock);

	/* Walk through the list and look for a matching entry */
	list_for_each(tmp, &rslist) {
		rs = list_entry(tmp, struct rs_control, list);
		if (symsize != rs->mm)
			continue;
		if (gfpoly != rs->gfpoly)
			continue;
		if (fcr != rs->fcr)
			continue;
		if (prim != rs->prim)
			continue;
		if (nroots != rs->nroots)
			continue;
		/* We have a matching one already */
		rs->users++;
		goto out;
	}

	/* Create a new one */
	rs = rs_init(symsize, gfpoly, fcr, prim, nroots);
	if (rs) {
		rs->users = 1;
		list_add(&rs->list, &rslist);
	}
out:
	up(&rslistlock);
	return rs;
}

#ifdef CONFIG_REED_SOLOMON_ENC8
/**
 *  encode_rs8 - Calculate the parity for data values (8bit data width)
 *
 *  @rs:	the rs control structure
 *  @data:	data field of a given type
 *  @len:	data length
 *  @par:	parity data, must be initialized by caller (usually all 0)
 *  @invmsk:	invert data mask (will be xored on data)
 *
 *  The parity uses a uint16_t data type to enable
 *  symbol size > 8. The calling code must take care of encoding of the
 *  syndrome result for storage itself.
 */
int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
	       uint16_t invmsk)
{
#include "encode_rs.c"
}
EXPORT_SYMBOL_GPL(encode_rs8);
#endif

#ifdef CONFIG_REED_SOLOMON_DEC8
/**
 *  decode_rs8 - Decode codeword (8bit data width)
 *
 *  @rs:	the rs control structure
 *  @data:	data field of a given type
 *  @par:	received parity data field
 *  @len:	data length
 *  @s:		syndrome data field (if NULL, syndrome is calculated)
 *  @no_eras:	number of erasures
 *  @eras_pos:	position of erasures, can be NULL
 *  @invmsk:	invert data mask (will be xored on data, not on parity!)
 *  @corr:	buffer to store correction bitmask on eras_pos
 *
 *  The syndrome and parity uses a uint16_t data type to enable
 *  symbol size > 8. The calling code must take care of decoding of the
 *  syndrome result and the received parity before calling this code.
 */
int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
	       uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
	       uint16_t *corr)
{
#include "decode_rs.c"
}
EXPORT_SYMBOL_GPL(decode_rs8);
#endif

#ifdef CONFIG_REED_SOLOMON_ENC16
/**
 *  encode_rs16 - Calculate the parity for data values (16bit data width)
 *
 *  @rs:	the rs control structure
 *  @data:	data field of a given type
 *  @len:	data length
 *  @par:	parity data, must be initialized by caller (usually all 0)
 *  @invmsk:	invert data mask (will be xored on data, not on parity!)
 *
 *  Each field in the data array contains up to symbol size bits of valid data.
 */
int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
	uint16_t invmsk)
{
#include "encode_rs.c"
}
EXPORT_SYMBOL_GPL(encode_rs16);
#endif

#ifdef CONFIG_REED_SOLOMON_DEC16
/**
 *  decode_rs16 - Decode codeword (16bit data width)
 *
 *  @rs:	the rs control structure
 *  @data:	data field of a given type
 *  @par:	received parity data field
 *  @len:	data length
 *  @s:		syndrome data field (if NULL, syndrome is calculated)
 *  @no_eras:	number of erasures
 *  @eras_pos:	position of erasures, can be NULL
 *  @invmsk:	invert data mask (will be xored on data, not on parity!)
 *  @corr:	buffer to store correction bitmask on eras_pos
 *
 *  Each field in the data array contains up to symbol size bits of valid data.
 */
int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
		uint16_t *corr)
{
#include "decode_rs.c"
}
EXPORT_SYMBOL_GPL(decode_rs16);
#endif

EXPORT_SYMBOL_GPL(init_rs);
EXPORT_SYMBOL_GPL(free_rs);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
MODULE_AUTHOR("Phil Karn, Thomas Gleixner");

OpenPOWER on IntegriCloud