/*
* lib/reed_solomon/rslib.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 <asm/semaphore.h>
/* This list holds all currently allocated rs control structures */
static LIST_HEAD (rslist);
/* Protection for the list */
static DECLARE_MUTEX(rslistlock);
/**
* rs_init - Initialize a Reed-Solomon codec
*
* @symsize: symbol size, bits (1-8)
* @gfpoly: Field generator polynomial coefficients
* @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 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;
/* 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 */
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;
}
/* If it's not primitive, exit */
if(sr != 1)
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 its not longer used
*
* @rs: the control structure which is not longer used by the
* caller
*/
void free_rs(struct rs_control *rs)
{
down(&rslistlock);
rs->users--;
if(!rs->users) {
list_del(&rs->list);
kfree(rs->alpha_to);
kfree(rs->index_of);
kfree(rs->genpoly);
kfree(rs);
}
up(&rslistlock);
}
/**
* 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)
{
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;
down(&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 (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, fcr, prim, nroots);
if (rs) {
rs->users = 1;
list_add(&rs->list, &rslist);
}
out:
up(&rslistlock);
return rs;
}
#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.
*/
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.
*/
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(free_rs);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
MODULE_AUTHOR("Phil Karn, Thomas Gleixner");
