ia64/linux-2.6.18-xen.hg

view lib/reed_solomon/reed_solomon.c @ 912:dd42cdb0ab89

[IA64] Build blktap2 driver by default in x86 builds.

add CONFIG_XEN_BLKDEV_TAP2=y to buildconfigs/linux-defconfig_xen_ia64.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
author Isaku Yamahata <yamahata@valinux.co.jp>
date Mon Jun 29 12:09:16 2009 +0900 (2009-06-29)
parents 831230e53067
children
line source
1 /*
2 * lib/reed_solomon/rslib.c
3 *
4 * Overview:
5 * Generic Reed Solomon encoder / decoder library
6 *
7 * Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
8 *
9 * Reed Solomon code lifted from reed solomon library written by Phil Karn
10 * Copyright 2002 Phil Karn, KA9Q
11 *
12 * $Id: rslib.c,v 1.7 2005/11/07 11:14:59 gleixner Exp $
13 *
14 * This program is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU General Public License version 2 as
16 * published by the Free Software Foundation.
17 *
18 * Description:
19 *
20 * The generic Reed Solomon library provides runtime configurable
21 * encoding / decoding of RS codes.
22 * Each user must call init_rs to get a pointer to a rs_control
23 * structure for the given rs parameters. This structure is either
24 * generated or a already available matching control structure is used.
25 * If a structure is generated then the polynomial arrays for
26 * fast encoding / decoding are built. This can take some time so
27 * make sure not to call this function from a time critical path.
28 * Usually a module / driver should initialize the necessary
29 * rs_control structure on module / driver init and release it
30 * on exit.
31 * The encoding puts the calculated syndrome into a given syndrome
32 * buffer.
33 * The decoding is a two step process. The first step calculates
34 * the syndrome over the received (data + syndrome) and calls the
35 * second stage, which does the decoding / error correction itself.
36 * Many hw encoders provide a syndrome calculation over the received
37 * data + syndrome and can call the second stage directly.
38 *
39 */
41 #include <linux/errno.h>
42 #include <linux/kernel.h>
43 #include <linux/init.h>
44 #include <linux/module.h>
45 #include <linux/rslib.h>
46 #include <linux/slab.h>
47 #include <linux/mutex.h>
48 #include <asm/semaphore.h>
50 /* This list holds all currently allocated rs control structures */
51 static LIST_HEAD (rslist);
52 /* Protection for the list */
53 static DEFINE_MUTEX(rslistlock);
55 /**
56 * rs_init - Initialize a Reed-Solomon codec
57 * @symsize: symbol size, bits (1-8)
58 * @gfpoly: Field generator polynomial coefficients
59 * @fcr: first root of RS code generator polynomial, index form
60 * @prim: primitive element to generate polynomial roots
61 * @nroots: RS code generator polynomial degree (number of roots)
62 *
63 * Allocate a control structure and the polynom arrays for faster
64 * en/decoding. Fill the arrays according to the given parameters.
65 */
66 static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
67 int prim, int nroots)
68 {
69 struct rs_control *rs;
70 int i, j, sr, root, iprim;
72 /* Allocate the control structure */
73 rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL);
74 if (rs == NULL)
75 return NULL;
77 INIT_LIST_HEAD(&rs->list);
79 rs->mm = symsize;
80 rs->nn = (1 << symsize) - 1;
81 rs->fcr = fcr;
82 rs->prim = prim;
83 rs->nroots = nroots;
84 rs->gfpoly = gfpoly;
86 /* Allocate the arrays */
87 rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
88 if (rs->alpha_to == NULL)
89 goto errrs;
91 rs->index_of = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
92 if (rs->index_of == NULL)
93 goto erralp;
95 rs->genpoly = kmalloc(sizeof(uint16_t) * (rs->nroots + 1), GFP_KERNEL);
96 if(rs->genpoly == NULL)
97 goto erridx;
99 /* Generate Galois field lookup tables */
100 rs->index_of[0] = rs->nn; /* log(zero) = -inf */
101 rs->alpha_to[rs->nn] = 0; /* alpha**-inf = 0 */
102 sr = 1;
103 for (i = 0; i < rs->nn; i++) {
104 rs->index_of[sr] = i;
105 rs->alpha_to[i] = sr;
106 sr <<= 1;
107 if (sr & (1 << symsize))
108 sr ^= gfpoly;
109 sr &= rs->nn;
110 }
111 /* If it's not primitive, exit */
112 if(sr != 1)
113 goto errpol;
115 /* Find prim-th root of 1, used in decoding */
116 for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
117 /* prim-th root of 1, index form */
118 rs->iprim = iprim / prim;
120 /* Form RS code generator polynomial from its roots */
121 rs->genpoly[0] = 1;
122 for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
123 rs->genpoly[i + 1] = 1;
124 /* Multiply rs->genpoly[] by @**(root + x) */
125 for (j = i; j > 0; j--) {
126 if (rs->genpoly[j] != 0) {
127 rs->genpoly[j] = rs->genpoly[j -1] ^
128 rs->alpha_to[rs_modnn(rs,
129 rs->index_of[rs->genpoly[j]] + root)];
130 } else
131 rs->genpoly[j] = rs->genpoly[j - 1];
132 }
133 /* rs->genpoly[0] can never be zero */
134 rs->genpoly[0] =
135 rs->alpha_to[rs_modnn(rs,
136 rs->index_of[rs->genpoly[0]] + root)];
137 }
138 /* convert rs->genpoly[] to index form for quicker encoding */
139 for (i = 0; i <= nroots; i++)
140 rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
141 return rs;
143 /* Error exit */
144 errpol:
145 kfree(rs->genpoly);
146 erridx:
147 kfree(rs->index_of);
148 erralp:
149 kfree(rs->alpha_to);
150 errrs:
151 kfree(rs);
152 return NULL;
153 }
156 /**
157 * free_rs - Free the rs control structure, if it is no longer used
158 * @rs: the control structure which is not longer used by the
159 * caller
160 */
161 void free_rs(struct rs_control *rs)
162 {
163 mutex_lock(&rslistlock);
164 rs->users--;
165 if(!rs->users) {
166 list_del(&rs->list);
167 kfree(rs->alpha_to);
168 kfree(rs->index_of);
169 kfree(rs->genpoly);
170 kfree(rs);
171 }
172 mutex_unlock(&rslistlock);
173 }
175 /**
176 * init_rs - Find a matching or allocate a new rs control structure
177 * @symsize: the symbol size (number of bits)
178 * @gfpoly: the extended Galois field generator polynomial coefficients,
179 * with the 0th coefficient in the low order bit. The polynomial
180 * must be primitive;
181 * @fcr: the first consecutive root of the rs code generator polynomial
182 * in index form
183 * @prim: primitive element to generate polynomial roots
184 * @nroots: RS code generator polynomial degree (number of roots)
185 */
186 struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
187 int nroots)
188 {
189 struct list_head *tmp;
190 struct rs_control *rs;
192 /* Sanity checks */
193 if (symsize < 1)
194 return NULL;
195 if (fcr < 0 || fcr >= (1<<symsize))
196 return NULL;
197 if (prim <= 0 || prim >= (1<<symsize))
198 return NULL;
199 if (nroots < 0 || nroots >= (1<<symsize))
200 return NULL;
202 mutex_lock(&rslistlock);
204 /* Walk through the list and look for a matching entry */
205 list_for_each(tmp, &rslist) {
206 rs = list_entry(tmp, struct rs_control, list);
207 if (symsize != rs->mm)
208 continue;
209 if (gfpoly != rs->gfpoly)
210 continue;
211 if (fcr != rs->fcr)
212 continue;
213 if (prim != rs->prim)
214 continue;
215 if (nroots != rs->nroots)
216 continue;
217 /* We have a matching one already */
218 rs->users++;
219 goto out;
220 }
222 /* Create a new one */
223 rs = rs_init(symsize, gfpoly, fcr, prim, nroots);
224 if (rs) {
225 rs->users = 1;
226 list_add(&rs->list, &rslist);
227 }
228 out:
229 mutex_unlock(&rslistlock);
230 return rs;
231 }
233 #ifdef CONFIG_REED_SOLOMON_ENC8
234 /**
235 * encode_rs8 - Calculate the parity for data values (8bit data width)
236 * @rs: the rs control structure
237 * @data: data field of a given type
238 * @len: data length
239 * @par: parity data, must be initialized by caller (usually all 0)
240 * @invmsk: invert data mask (will be xored on data)
241 *
242 * The parity uses a uint16_t data type to enable
243 * symbol size > 8. The calling code must take care of encoding of the
244 * syndrome result for storage itself.
245 */
246 int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
247 uint16_t invmsk)
248 {
249 #include "encode_rs.c"
250 }
251 EXPORT_SYMBOL_GPL(encode_rs8);
252 #endif
254 #ifdef CONFIG_REED_SOLOMON_DEC8
255 /**
256 * decode_rs8 - Decode codeword (8bit data width)
257 * @rs: the rs control structure
258 * @data: data field of a given type
259 * @par: received parity data field
260 * @len: data length
261 * @s: syndrome data field (if NULL, syndrome is calculated)
262 * @no_eras: number of erasures
263 * @eras_pos: position of erasures, can be NULL
264 * @invmsk: invert data mask (will be xored on data, not on parity!)
265 * @corr: buffer to store correction bitmask on eras_pos
266 *
267 * The syndrome and parity uses a uint16_t data type to enable
268 * symbol size > 8. The calling code must take care of decoding of the
269 * syndrome result and the received parity before calling this code.
270 */
271 int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
272 uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
273 uint16_t *corr)
274 {
275 #include "decode_rs.c"
276 }
277 EXPORT_SYMBOL_GPL(decode_rs8);
278 #endif
280 #ifdef CONFIG_REED_SOLOMON_ENC16
281 /**
282 * encode_rs16 - Calculate the parity for data values (16bit data width)
283 * @rs: the rs control structure
284 * @data: data field of a given type
285 * @len: data length
286 * @par: parity data, must be initialized by caller (usually all 0)
287 * @invmsk: invert data mask (will be xored on data, not on parity!)
288 *
289 * Each field in the data array contains up to symbol size bits of valid data.
290 */
291 int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
292 uint16_t invmsk)
293 {
294 #include "encode_rs.c"
295 }
296 EXPORT_SYMBOL_GPL(encode_rs16);
297 #endif
299 #ifdef CONFIG_REED_SOLOMON_DEC16
300 /**
301 * decode_rs16 - Decode codeword (16bit data width)
302 * @rs: the rs control structure
303 * @data: data field of a given type
304 * @par: received parity data field
305 * @len: data length
306 * @s: syndrome data field (if NULL, syndrome is calculated)
307 * @no_eras: number of erasures
308 * @eras_pos: position of erasures, can be NULL
309 * @invmsk: invert data mask (will be xored on data, not on parity!)
310 * @corr: buffer to store correction bitmask on eras_pos
311 *
312 * Each field in the data array contains up to symbol size bits of valid data.
313 */
314 int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
315 uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
316 uint16_t *corr)
317 {
318 #include "decode_rs.c"
319 }
320 EXPORT_SYMBOL_GPL(decode_rs16);
321 #endif
323 EXPORT_SYMBOL_GPL(init_rs);
324 EXPORT_SYMBOL_GPL(free_rs);
326 MODULE_LICENSE("GPL");
327 MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
328 MODULE_AUTHOR("Phil Karn, Thomas Gleixner");