lib/reed_solomon/reed_solomon.c

   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  */
  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 #include <asm/semaphore.h>
  49
  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);
  54
  55 /**
  56  * rs_init - Initialize a Reed-Solomon codec
  57  *
  58  * @symsize:    symbol size, bits (1-8)
  59  * @gfpoly:     Field generator polynomial coefficients
  60  * @fcr:        first root of RS code generator polynomial, index form
  61  * @prim:       primitive element to generate polynomial roots
  62  * @nroots:     RS code generator polynomial degree (number of roots)
  63  *
  64  * Allocate a control structure and the polynom arrays for faster
  65  * en/decoding. Fill the arrays according to the given parameters
  66  */
  67 static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
  68                                    int prim, int nroots)
  69 {
  70         struct rs_control *rs;
  71         int i, j, sr, root, iprim;
  72
  73         /* Allocate the control structure */
  74         rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL);
  75         if (rs == NULL)
  76                 return NULL;
  77
  78         INIT_LIST_HEAD(&rs->list);
  79
  80         rs->mm = symsize;
  81         rs->nn = (1 << symsize) - 1;
  82         rs->fcr = fcr;
  83         rs->prim = prim;
  84         rs->nroots = nroots;
  85         rs->gfpoly = gfpoly;
  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         sr = 1;
 104         for (i = 0; i < rs->nn; i++) {
 105                 rs->index_of[sr] = i;
 106                 rs->alpha_to[i] = sr;
 107                 sr <<= 1;
 108                 if (sr & (1 << symsize))
 109                         sr ^= gfpoly;
 110                 sr &= rs->nn;
 111         }
 112         /* If it's not primitive, exit */
 113         if(sr != 1)
 114                 goto errpol;
 115
 116         /* Find prim-th root of 1, used in decoding */
 117         for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
 118         /* prim-th root of 1, index form */
 119         rs->iprim = iprim / prim;
 120
 121         /* Form RS code generator polynomial from its roots */
 122         rs->genpoly[0] = 1;
 123         for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
 124                 rs->genpoly[i + 1] = 1;
 125                 /* Multiply rs->genpoly[] by  @**(root + x) */
 126                 for (j = i; j > 0; j--) {
 127                         if (rs->genpoly[j] != 0) {
 128                                 rs->genpoly[j] = rs->genpoly[j -1] ^
 129                                         rs->alpha_to[rs_modnn(rs,
 130                                         rs->index_of[rs->genpoly[j]] + root)];
 131                         } else
 132                                 rs->genpoly[j] = rs->genpoly[j - 1];
 133                 }
 134                 /* rs->genpoly[0] can never be zero */
 135                 rs->genpoly[0] =
 136                         rs->alpha_to[rs_modnn(rs,
 137                                 rs->index_of[rs->genpoly[0]] + root)];
 138         }
 139         /* convert rs->genpoly[] to index form for quicker encoding */
 140         for (i = 0; i <= nroots; i++)
 141                 rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
 142         return rs;
 143
 144         /* Error exit */
 145 errpol:
 146         kfree(rs->genpoly);
 147 erridx:
 148         kfree(rs->index_of);
 149 erralp:
 150         kfree(rs->alpha_to);
 151 errrs:
 152         kfree(rs);
 153         return NULL;
 154 }
 155
 156
 157 /**
 158  *  free_rs - Free the rs control structure, if its not longer used
 159  *
 160  *  @rs:        the control structure which is not longer used by the
 161  *              caller
 162  */
 163 void free_rs(struct rs_control *rs)
 164 {
 165         mutex_lock(&rslistlock);
 166         rs->users--;
 167         if(!rs->users) {
 168                 list_del(&rs->list);
 169                 kfree(rs->alpha_to);
 170                 kfree(rs->index_of);
 171                 kfree(rs->genpoly);
 172                 kfree(rs);
 173         }
 174         mutex_unlock(&rslistlock);
 175 }
 176
 177 /**
 178  * init_rs - Find a matching or allocate a new rs control structure
 179  *
 180  *  @symsize:   the symbol size (number of bits)
 181  *  @gfpoly:    the extended Galois field generator polynomial coefficients,
 182  *              with the 0th coefficient in the low order bit. The polynomial
 183  *              must be primitive;
 184  *  @fcr:       the first consecutive root of the rs code generator polynomial
 185  *              in index form
 186  *  @prim:      primitive element to generate polynomial roots
 187  *  @nroots:    RS code generator polynomial degree (number of roots)
 188  */
 189 struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
 190                            int nroots)
 191 {
 192         struct list_head        *tmp;
 193         struct rs_control       *rs;
 194
 195         /* Sanity checks */
 196         if (symsize < 1)
 197                 return NULL;
 198         if (fcr < 0 || fcr >= (1<<symsize))
 199                 return NULL;
 200         if (prim <= 0 || prim >= (1<<symsize))
 201                 return NULL;
 202         if (nroots < 0 || nroots >= (1<<symsize))
 203                 return NULL;
 204
 205         mutex_lock(&rslistlock);
 206
 207         /* Walk through the list and look for a matching entry */
 208         list_for_each(tmp, &rslist) {
 209                 rs = list_entry(tmp, struct rs_control, list);
 210                 if (symsize != rs->mm)
 211                         continue;
 212                 if (gfpoly != rs->gfpoly)
 213                         continue;
 214                 if (fcr != rs->fcr)
 215                         continue;
 216                 if (prim != rs->prim)
 217                         continue;
 218                 if (nroots != rs->nroots)
 219                         continue;
 220                 /* We have a matching one already */
 221                 rs->users++;
 222                 goto out;
 223         }
 224
 225         /* Create a new one */
 226         rs = rs_init(symsize, gfpoly, fcr, prim, nroots);
 227         if (rs) {
 228                 rs->users = 1;
 229                 list_add(&rs->list, &rslist);
 230         }
 231 out:
 232         mutex_unlock(&rslistlock);
 233         return rs;
 234 }
 235
 236 #ifdef CONFIG_REED_SOLOMON_ENC8
 237 /**
 238  *  encode_rs8 - Calculate the parity for data values (8bit data width)
 239  *
 240  *  @rs:        the rs control structure
 241  *  @data:      data field of a given type
 242  *  @len:       data length
 243  *  @par:       parity data, must be initialized by caller (usually all 0)
 244  *  @invmsk:    invert data mask (will be xored on data)
 245  *
 246  *  The parity uses a uint16_t data type to enable
 247  *  symbol size > 8. The calling code must take care of encoding of the
 248  *  syndrome result for storage itself.
 249  */
 250 int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
 251                uint16_t invmsk)
 252 {
 253 #include "encode_rs.c"
 254 }
 255 EXPORT_SYMBOL_GPL(encode_rs8);
 256 #endif
 257
 258 #ifdef CONFIG_REED_SOLOMON_DEC8
 259 /**
 260  *  decode_rs8 - Decode codeword (8bit data width)
 261  *
 262  *  @rs:        the rs control structure
 263  *  @data:      data field of a given type
 264  *  @par:       received parity data field
 265  *  @len:       data length
 266  *  @s:         syndrome data field (if NULL, syndrome is calculated)
 267  *  @no_eras:   number of erasures
 268  *  @eras_pos:  position of erasures, can be NULL
 269  *  @invmsk:    invert data mask (will be xored on data, not on parity!)
 270  *  @corr:      buffer to store correction bitmask on eras_pos
 271  *
 272  *  The syndrome and parity uses a uint16_t data type to enable
 273  *  symbol size > 8. The calling code must take care of decoding of the
 274  *  syndrome result and the received parity before calling this code.
 275  */
 276 int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
 277                uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 278                uint16_t *corr)
 279 {
 280 #include "decode_rs.c"
 281 }
 282 EXPORT_SYMBOL_GPL(decode_rs8);
 283 #endif
 284
 285 #ifdef CONFIG_REED_SOLOMON_ENC16
 286 /**
 287  *  encode_rs16 - Calculate the parity for data values (16bit data width)
 288  *
 289  *  @rs:        the rs control structure
 290  *  @data:      data field of a given type
 291  *  @len:       data length
 292  *  @par:       parity data, must be initialized by caller (usually all 0)
 293  *  @invmsk:    invert data mask (will be xored on data, not on parity!)
 294  *
 295  *  Each field in the data array contains up to symbol size bits of valid data.
 296  */
 297 int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
 298         uint16_t invmsk)
 299 {
 300 #include "encode_rs.c"
 301 }
 302 EXPORT_SYMBOL_GPL(encode_rs16);
 303 #endif
 304
 305 #ifdef CONFIG_REED_SOLOMON_DEC16
 306 /**
 307  *  decode_rs16 - Decode codeword (16bit data width)
 308  *
 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  *  Each field in the data array contains up to symbol size bits of valid data.
 320  */
 321 int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
 322                 uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 323                 uint16_t *corr)
 324 {
 325 #include "decode_rs.c"
 326 }
 327 EXPORT_SYMBOL_GPL(decode_rs16);
 328 #endif
 329
 330 EXPORT_SYMBOL_GPL(init_rs);
 331 EXPORT_SYMBOL_GPL(free_rs);
 332
 333 MODULE_LICENSE("GPL");
 334 MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
 335 MODULE_AUTHOR("Phil Karn, Thomas Gleixner");
 336