/*
 * lib/reed_solomon/reed_solomon.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 <linux/mutex.h>

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

/**
 * rs_init - Initialize a Reed-Solomon codec
 * @symsize:    symbol size, bits (1-8)
 * @gfpoly:     Field generator polynomial coefficients
 * @gffunc:     Field generator function
 * @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 (*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;
}


/**
 *  free_rs - Free the rs control structure, if it is no longer used
 *  @rs:        the control structure which is not longer used by the
 *              caller
 */
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);
}

/**
 * init_rs_internal - 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;
 *  @gffunc:    pointer to function to generate the next field element,
 *              or the multiplicative identity element if given 0.  Used
 *              instead of gfpoly if gfpoly is 0
 *  @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)
 */
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;
}

/**
 * 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)
{
        return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
}

/**
 * init_rs_non_canonical - Find a matching or allocate a new rs control
 *                         structure, for fields with non-canonical
 *                         representation
 *  @symsize:   the symbol size (number of bits)
 *  @gffunc:    pointer to function to generate the next field element,
 *              or the multiplicative identity element if given 0.  Used
 *              instead of gfpoly if gfpoly is 0
 *  @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_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
/**
 *  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.
 *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
 */
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.
 *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
 */
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");