reed_solomon.c

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/*
 * lib/reed_solomon/reed_solomon.c
 *
 * Overview:
 *   Generic Reed Solomon encoder / decoder library
 *
 * Copyright (C) 2004 Thomas Gleixner ([email protected])
 *
 * 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 <linux/mutex.h>

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

static struct rs_control *rs_init(int symsize, int gfpoly, int (*gffunc)(int),
                                  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;
    rs->gffunc = gffunc;

    /* 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 */
    if (gfpoly) {
        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;
        }
    } else {
        sr = gffunc(0);
        for (i = 0; i < rs->nn; i++) {
            rs->index_of[sr] = i;
            rs->alpha_to[i] = sr;
            sr = gffunc(sr);
        }
    }
    /* If it's not primitive, exit */
    if(sr != rs->alpha_to[0])
        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;
}


void free_rs(struct rs_control *rs)
{
    mutex_lock(&rslistlock);
    rs->users--;
    if(!rs->users) {
        list_del(&rs->list);
        kfree(rs->alpha_to);
        kfree(rs->index_of);
        kfree(rs->genpoly);
        kfree(rs);
    }
    mutex_unlock(&rslistlock);
}

static struct rs_control *init_rs_internal(int symsize, int gfpoly,
                                           int (*gffunc)(int), 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;

    mutex_lock(&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 (gffunc != rs->gffunc)
            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, gffunc, fcr, prim, nroots);
    if (rs) {
        rs->users = 1;
        list_add(&rs->list, &rslist);
    }
out:
    mutex_unlock(&rslistlock);
    return rs;
}

struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
                           int nroots)
{
    return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
}

struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
                                         int fcr, int prim, int nroots)
{
    return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots);
}

#ifdef CONFIG_REED_SOLOMON_ENC8

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

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

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

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(init_rs_non_canonical);
EXPORT_SYMBOL_GPL(free_rs);

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