lib/reed_solomon/reed_solomon.c

   1 /*
   2  * lib/reed_solomon/reed_solomon.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  */
  40
  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
  49 /* This list holds all currently allocated rs control structures */
  50 static LIST_HEAD (rslist);
  51 /* Protection for the list */
  52 static DEFINE_MUTEX(rslistlock);
  53
  54 /**
  55  * rs_init - Initialize a Reed-Solomon codec
  56  * @symsize:    symbol size, bits (1-8)
  57  * @gfpoly:     Field generator polynomial coefficients
  58  * @gffunc:     Field generator function
  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 (*gffunc)(int),
  67                                   int fcr, int prim, int nroots)
  68 {
  69         struct rs_control *rs;
  70         int i, j, sr, root, iprim;
  71
  72         /* Allocate the control structure */
  73         rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL);
  74         if (rs == NULL)
  75                 return NULL;
  76
  77         INIT_LIST_HEAD(&rs->list);
  78
  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;
  85         rs->gffunc = gffunc;
  86
  87         /* Allocate the arrays */
  88         rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
  89         if (rs->alpha_to == NULL)
  90                 goto errrs;
  91
  92         rs->index_of = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
  93         if (rs->index_of == NULL)
  94                 goto erralp;
  95
  96         rs->genpoly = kmalloc(sizeof(uint16_t) * (rs->nroots + 1), GFP_KERNEL);
  97         if(rs->genpoly == NULL)
  98                 goto erridx;
  99
 100         /* Generate Galois field lookup tables */
 101         rs->index_of[0] = rs->nn;       /* log(zero) = -inf */
 102         rs->alpha_to[rs->nn] = 0;       /* alpha**-inf = 0 */
 103         if (gfpoly) {
 104                 sr = 1;
 105                 for (i = 0; i < rs->nn; i++) {
 106                         rs->index_of[sr] = i;
 107                         rs->alpha_to[i] = sr;
 108                         sr <<= 1;
 109                         if (sr & (1 << symsize))
 110                                 sr ^= gfpoly;
 111                         sr &= rs->nn;
 112                 }
 113         } else {
 114                 sr = gffunc(0);
 115                 for (i = 0; i < rs->nn; i++) {
 116                         rs->index_of[sr] = i;
 117                         rs->alpha_to[i] = sr;
 118                         sr = gffunc(sr);
 119                 }
 120         }
 121         /* If it's not primitive, exit */
 122         if(sr != rs->alpha_to[0])
 123                 goto errpol;
 124
 125         /* Find prim-th root of 1, used in decoding */
 126         for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
 127         /* prim-th root of 1, index form */
 128         rs->iprim = iprim / prim;
 129
 130         /* Form RS code generator polynomial from its roots */
 131         rs->genpoly[0] = 1;
 132         for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
 133                 rs->genpoly[i + 1] = 1;
 134                 /* Multiply rs->genpoly[] by  @**(root + x) */
 135                 for (j = i; j > 0; j--) {
 136                         if (rs->genpoly[j] != 0) {
 137                                 rs->genpoly[j] = rs->genpoly[j -1] ^
 138                                         rs->alpha_to[rs_modnn(rs,
 139                                         rs->index_of[rs->genpoly[j]] + root)];
 140                         } else
 141                                 rs->genpoly[j] = rs->genpoly[j - 1];
 142                 }
 143                 /* rs->genpoly[0] can never be zero */
 144                 rs->genpoly[0] =
 145                         rs->alpha_to[rs_modnn(rs,
 146                                 rs->index_of[rs->genpoly[0]] + root)];
 147         }
 148         /* convert rs->genpoly[] to index form for quicker encoding */
 149         for (i = 0; i <= nroots; i++)
 150                 rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
 151         return rs;
 152
 153         /* Error exit */
 154 errpol:
 155         kfree(rs->genpoly);
 156 erridx:
 157         kfree(rs->index_of);
 158 erralp:
 159         kfree(rs->alpha_to);
 160 errrs:
 161         kfree(rs);
 162         return NULL;
 163 }
 164
 165
 166 /**
 167  *  free_rs - Free the rs control structure, if it is no longer used
 168  *  @rs:        the control structure which is not longer used by the
 169  *              caller
 170  */
 171 void free_rs(struct rs_control *rs)
 172 {
 173         mutex_lock(&rslistlock);
 174         rs->users--;
 175         if(!rs->users) {
 176                 list_del(&rs->list);
 177                 kfree(rs->alpha_to);
 178                 kfree(rs->index_of);
 179                 kfree(rs->genpoly);
 180                 kfree(rs);
 181         }
 182         mutex_unlock(&rslistlock);
 183 }
 184
 185 /**
 186  * init_rs_internal - Find a matching or allocate a new rs control structure
 187  *  @symsize:   the symbol size (number of bits)
 188  *  @gfpoly:    the extended Galois field generator polynomial coefficients,
 189  *              with the 0th coefficient in the low order bit. The polynomial
 190  *              must be primitive;
 191  *  @gffunc:    pointer to function to generate the next field element,
 192  *              or the multiplicative identity element if given 0.  Used
 193  *              instead of gfpoly if gfpoly is 0
 194  *  @fcr:       the first consecutive root of the rs code generator polynomial
 195  *              in index form
 196  *  @prim:      primitive element to generate polynomial roots
 197  *  @nroots:    RS code generator polynomial degree (number of roots)
 198  */
 199 static struct rs_control *init_rs_internal(int symsize, int gfpoly,
 200                                            int (*gffunc)(int), int fcr,
 201                                            int prim, int nroots)
 202 {
 203         struct list_head        *tmp;
 204         struct rs_control       *rs;
 205
 206         /* Sanity checks */
 207         if (symsize < 1)
 208                 return NULL;
 209         if (fcr < 0 || fcr >= (1<<symsize))
 210                 return NULL;
 211         if (prim <= 0 || prim >= (1<<symsize))
 212                 return NULL;
 213         if (nroots < 0 || nroots >= (1<<symsize))
 214                 return NULL;
 215
 216         mutex_lock(&rslistlock);
 217
 218         /* Walk through the list and look for a matching entry */
 219         list_for_each(tmp, &rslist) {
 220                 rs = list_entry(tmp, struct rs_control, list);
 221                 if (symsize != rs->mm)
 222                         continue;
 223                 if (gfpoly != rs->gfpoly)
 224                         continue;
 225                 if (gffunc != rs->gffunc)
 226                         continue;
 227                 if (fcr != rs->fcr)
 228                         continue;
 229                 if (prim != rs->prim)
 230                         continue;
 231                 if (nroots != rs->nroots)
 232                         continue;
 233                 /* We have a matching one already */
 234                 rs->users++;
 235                 goto out;
 236         }
 237
 238         /* Create a new one */
 239         rs = rs_init(symsize, gfpoly, gffunc, fcr, prim, nroots);
 240         if (rs) {
 241                 rs->users = 1;
 242                 list_add(&rs->list, &rslist);
 243         }
 244 out:
 245         mutex_unlock(&rslistlock);
 246         return rs;
 247 }
 248
 249 /**
 250  * init_rs - Find a matching or allocate a new rs control structure
 251  *  @symsize:   the symbol size (number of bits)
 252  *  @gfpoly:    the extended Galois field generator polynomial coefficients,
 253  *              with the 0th coefficient in the low order bit. The polynomial
 254  *              must be primitive;
 255  *  @fcr:       the first consecutive root of the rs code generator polynomial
 256  *              in index form
 257  *  @prim:      primitive element to generate polynomial roots
 258  *  @nroots:    RS code generator polynomial degree (number of roots)
 259  */
 260 struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
 261                            int nroots)
 262 {
 263         return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
 264 }
 265
 266 /**
 267  * init_rs_non_canonical - Find a matching or allocate a new rs control
 268  *                         structure, for fields with non-canonical
 269  *                         representation
 270  *  @symsize:   the symbol size (number of bits)
 271  *  @gffunc:    pointer to function to generate the next field element,
 272  *              or the multiplicative identity element if given 0.  Used
 273  *              instead of gfpoly if gfpoly is 0
 274  *  @fcr:       the first consecutive root of the rs code generator polynomial
 275  *              in index form
 276  *  @prim:      primitive element to generate polynomial roots
 277  *  @nroots:    RS code generator polynomial degree (number of roots)
 278  */
 279 struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
 280                                          int fcr, int prim, int nroots)
 281 {
 282         return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots);
 283 }
 284
 285 #ifdef CONFIG_REED_SOLOMON_ENC8
 286 /**
 287  *  encode_rs8 - Calculate the parity for data values (8bit data width)
 288  *  @rs:        the rs control structure
 289  *  @data:      data field of a given type
 290  *  @len:       data length
 291  *  @par:       parity data, must be initialized by caller (usually all 0)
 292  *  @invmsk:    invert data mask (will be xored on data)
 293  *
 294  *  The parity uses a uint16_t data type to enable
 295  *  symbol size > 8. The calling code must take care of encoding of the
 296  *  syndrome result for storage itself.
 297  */
 298 int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
 299                uint16_t invmsk)
 300 {
 301 #include "encode_rs.c"
 302 }
 303 EXPORT_SYMBOL_GPL(encode_rs8);
 304 #endif
 305
 306 #ifdef CONFIG_REED_SOLOMON_DEC8
 307 /**
 308  *  decode_rs8 - Decode codeword (8bit data width)
 309  *  @rs:        the rs control structure
 310  *  @data:      data field of a given type
 311  *  @par:       received parity data field
 312  *  @len:       data length
 313  *  @s:         syndrome data field (if NULL, syndrome is calculated)
 314  *  @no_eras:   number of erasures
 315  *  @eras_pos:  position of erasures, can be NULL
 316  *  @invmsk:    invert data mask (will be xored on data, not on parity!)
 317  *  @corr:      buffer to store correction bitmask on eras_pos
 318  *
 319  *  The syndrome and parity uses a uint16_t data type to enable
 320  *  symbol size > 8. The calling code must take care of decoding of the
 321  *  syndrome result and the received parity before calling this code.
 322  *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
 323  */
 324 int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
 325                uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 326                uint16_t *corr)
 327 {
 328 #include "decode_rs.c"
 329 }
 330 EXPORT_SYMBOL_GPL(decode_rs8);
 331 #endif
 332
 333 #ifdef CONFIG_REED_SOLOMON_ENC16
 334 /**
 335  *  encode_rs16 - Calculate the parity for data values (16bit data width)
 336  *  @rs:        the rs control structure
 337  *  @data:      data field of a given type
 338  *  @len:       data length
 339  *  @par:       parity data, must be initialized by caller (usually all 0)
 340  *  @invmsk:    invert data mask (will be xored on data, not on parity!)
 341  *
 342  *  Each field in the data array contains up to symbol size bits of valid data.
 343  */
 344 int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
 345         uint16_t invmsk)
 346 {
 347 #include "encode_rs.c"
 348 }
 349 EXPORT_SYMBOL_GPL(encode_rs16);
 350 #endif
 351
 352 #ifdef CONFIG_REED_SOLOMON_DEC16
 353 /**
 354  *  decode_rs16 - Decode codeword (16bit data width)
 355  *  @rs:        the rs control structure
 356  *  @data:      data field of a given type
 357  *  @par:       received parity data field
 358  *  @len:       data length
 359  *  @s:         syndrome data field (if NULL, syndrome is calculated)
 360  *  @no_eras:   number of erasures
 361  *  @eras_pos:  position of erasures, can be NULL
 362  *  @invmsk:    invert data mask (will be xored on data, not on parity!)
 363  *  @corr:      buffer to store correction bitmask on eras_pos
 364  *
 365  *  Each field in the data array contains up to symbol size bits of valid data.
 366  *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
 367  */
 368 int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
 369                 uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 370                 uint16_t *corr)
 371 {
 372 #include "decode_rs.c"
 373 }
 374 EXPORT_SYMBOL_GPL(decode_rs16);
 375 #endif
 376
 377 EXPORT_SYMBOL_GPL(init_rs);
 378 EXPORT_SYMBOL_GPL(init_rs_non_canonical);
 379 EXPORT_SYMBOL_GPL(free_rs);
 380
 381 MODULE_LICENSE("GPL");
 382 MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
 383 MODULE_AUTHOR("Phil Karn, Thomas Gleixner");
 384