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![Jörn Engel](/assets/img/avatar_default.png)
Magic numerical values are just bad style. Particularly so when undocumented. Signed-off-by: Jörn Engel <joern@logfs.org> Signed-off-by: David Woodhouse <dwmw2@infradead.org>
385 lines
12 KiB
C
385 lines
12 KiB
C
/*
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* lib/reed_solomon/reed_solomon.c
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*
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* Overview:
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* Generic Reed Solomon encoder / decoder library
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*
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* Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
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*
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* Reed Solomon code lifted from reed solomon library written by Phil Karn
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* Copyright 2002 Phil Karn, KA9Q
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*
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* $Id: rslib.c,v 1.7 2005/11/07 11:14:59 gleixner Exp $
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Description:
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*
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* The generic Reed Solomon library provides runtime configurable
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* encoding / decoding of RS codes.
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* Each user must call init_rs to get a pointer to a rs_control
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* structure for the given rs parameters. This structure is either
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* generated or a already available matching control structure is used.
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* If a structure is generated then the polynomial arrays for
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* fast encoding / decoding are built. This can take some time so
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* make sure not to call this function from a time critical path.
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* Usually a module / driver should initialize the necessary
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* rs_control structure on module / driver init and release it
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* on exit.
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* The encoding puts the calculated syndrome into a given syndrome
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* buffer.
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* The decoding is a two step process. The first step calculates
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* the syndrome over the received (data + syndrome) and calls the
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* second stage, which does the decoding / error correction itself.
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* Many hw encoders provide a syndrome calculation over the received
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* data + syndrome and can call the second stage directly.
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*
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*/
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#include <linux/errno.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/rslib.h>
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#include <linux/slab.h>
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#include <linux/mutex.h>
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#include <asm/semaphore.h>
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/* This list holds all currently allocated rs control structures */
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static LIST_HEAD (rslist);
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/* Protection for the list */
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static DEFINE_MUTEX(rslistlock);
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/**
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* rs_init - Initialize a Reed-Solomon codec
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* @symsize: symbol size, bits (1-8)
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* @gfpoly: Field generator polynomial coefficients
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* @gffunc: Field generator function
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* @fcr: first root of RS code generator polynomial, index form
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* @prim: primitive element to generate polynomial roots
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* @nroots: RS code generator polynomial degree (number of roots)
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*
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* Allocate a control structure and the polynom arrays for faster
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* en/decoding. Fill the arrays according to the given parameters.
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*/
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static struct rs_control *rs_init(int symsize, int gfpoly, int (*gffunc)(int),
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int fcr, int prim, int nroots)
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{
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struct rs_control *rs;
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int i, j, sr, root, iprim;
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/* Allocate the control structure */
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rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL);
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if (rs == NULL)
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return NULL;
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INIT_LIST_HEAD(&rs->list);
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rs->mm = symsize;
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rs->nn = (1 << symsize) - 1;
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rs->fcr = fcr;
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rs->prim = prim;
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rs->nroots = nroots;
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rs->gfpoly = gfpoly;
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rs->gffunc = gffunc;
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/* Allocate the arrays */
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rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
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if (rs->alpha_to == NULL)
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goto errrs;
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rs->index_of = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
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if (rs->index_of == NULL)
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goto erralp;
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rs->genpoly = kmalloc(sizeof(uint16_t) * (rs->nroots + 1), GFP_KERNEL);
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if(rs->genpoly == NULL)
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goto erridx;
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/* Generate Galois field lookup tables */
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rs->index_of[0] = rs->nn; /* log(zero) = -inf */
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rs->alpha_to[rs->nn] = 0; /* alpha**-inf = 0 */
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if (gfpoly) {
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sr = 1;
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for (i = 0; i < rs->nn; i++) {
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rs->index_of[sr] = i;
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rs->alpha_to[i] = sr;
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sr <<= 1;
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if (sr & (1 << symsize))
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sr ^= gfpoly;
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sr &= rs->nn;
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}
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} else {
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sr = gffunc(0);
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for (i = 0; i < rs->nn; i++) {
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rs->index_of[sr] = i;
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rs->alpha_to[i] = sr;
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sr = gffunc(sr);
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}
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}
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/* If it's not primitive, exit */
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if(sr != rs->alpha_to[0])
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goto errpol;
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/* Find prim-th root of 1, used in decoding */
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for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
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/* prim-th root of 1, index form */
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rs->iprim = iprim / prim;
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/* Form RS code generator polynomial from its roots */
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rs->genpoly[0] = 1;
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for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
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rs->genpoly[i + 1] = 1;
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/* Multiply rs->genpoly[] by @**(root + x) */
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for (j = i; j > 0; j--) {
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if (rs->genpoly[j] != 0) {
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rs->genpoly[j] = rs->genpoly[j -1] ^
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rs->alpha_to[rs_modnn(rs,
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rs->index_of[rs->genpoly[j]] + root)];
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} else
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rs->genpoly[j] = rs->genpoly[j - 1];
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}
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/* rs->genpoly[0] can never be zero */
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rs->genpoly[0] =
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rs->alpha_to[rs_modnn(rs,
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rs->index_of[rs->genpoly[0]] + root)];
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}
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/* convert rs->genpoly[] to index form for quicker encoding */
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for (i = 0; i <= nroots; i++)
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rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
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return rs;
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/* Error exit */
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errpol:
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kfree(rs->genpoly);
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erridx:
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kfree(rs->index_of);
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erralp:
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kfree(rs->alpha_to);
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errrs:
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kfree(rs);
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return NULL;
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}
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/**
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* free_rs - Free the rs control structure, if it is no longer used
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* @rs: the control structure which is not longer used by the
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* caller
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*/
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void free_rs(struct rs_control *rs)
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{
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mutex_lock(&rslistlock);
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rs->users--;
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if(!rs->users) {
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list_del(&rs->list);
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kfree(rs->alpha_to);
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kfree(rs->index_of);
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kfree(rs->genpoly);
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kfree(rs);
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}
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mutex_unlock(&rslistlock);
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}
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/**
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* init_rs_internal - Find a matching or allocate a new rs control structure
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* @symsize: the symbol size (number of bits)
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* @gfpoly: the extended Galois field generator polynomial coefficients,
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* with the 0th coefficient in the low order bit. The polynomial
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* must be primitive;
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* @gffunc: pointer to function to generate the next field element,
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* or the multiplicative identity element if given 0. Used
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* instead of gfpoly if gfpoly is 0
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* @fcr: the first consecutive root of the rs code generator polynomial
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* in index form
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* @prim: primitive element to generate polynomial roots
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* @nroots: RS code generator polynomial degree (number of roots)
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*/
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static struct rs_control *init_rs_internal(int symsize, int gfpoly,
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int (*gffunc)(int), int fcr,
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int prim, int nroots)
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{
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struct list_head *tmp;
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struct rs_control *rs;
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/* Sanity checks */
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if (symsize < 1)
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return NULL;
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if (fcr < 0 || fcr >= (1<<symsize))
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return NULL;
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if (prim <= 0 || prim >= (1<<symsize))
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return NULL;
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if (nroots < 0 || nroots >= (1<<symsize))
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return NULL;
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mutex_lock(&rslistlock);
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/* Walk through the list and look for a matching entry */
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list_for_each(tmp, &rslist) {
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rs = list_entry(tmp, struct rs_control, list);
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if (symsize != rs->mm)
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continue;
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if (gfpoly != rs->gfpoly)
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continue;
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if (gffunc != rs->gffunc)
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continue;
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if (fcr != rs->fcr)
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continue;
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if (prim != rs->prim)
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continue;
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if (nroots != rs->nroots)
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continue;
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/* We have a matching one already */
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rs->users++;
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goto out;
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}
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/* Create a new one */
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rs = rs_init(symsize, gfpoly, gffunc, fcr, prim, nroots);
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if (rs) {
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rs->users = 1;
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list_add(&rs->list, &rslist);
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}
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out:
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mutex_unlock(&rslistlock);
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return rs;
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}
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/**
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* init_rs - Find a matching or allocate a new rs control structure
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* @symsize: the symbol size (number of bits)
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* @gfpoly: the extended Galois field generator polynomial coefficients,
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* with the 0th coefficient in the low order bit. The polynomial
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* must be primitive;
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* @fcr: the first consecutive root of the rs code generator polynomial
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* in index form
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* @prim: primitive element to generate polynomial roots
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* @nroots: RS code generator polynomial degree (number of roots)
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*/
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struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
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int nroots)
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{
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return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
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}
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/**
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* init_rs_non_canonical - Find a matching or allocate a new rs control
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* structure, for fields with non-canonical
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* representation
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* @symsize: the symbol size (number of bits)
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* @gffunc: pointer to function to generate the next field element,
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* or the multiplicative identity element if given 0. Used
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* instead of gfpoly if gfpoly is 0
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* @fcr: the first consecutive root of the rs code generator polynomial
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* in index form
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* @prim: primitive element to generate polynomial roots
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* @nroots: RS code generator polynomial degree (number of roots)
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*/
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struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
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int fcr, int prim, int nroots)
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{
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return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots);
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}
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#ifdef CONFIG_REED_SOLOMON_ENC8
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/**
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* encode_rs8 - Calculate the parity for data values (8bit data width)
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* @rs: the rs control structure
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* @data: data field of a given type
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* @len: data length
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* @par: parity data, must be initialized by caller (usually all 0)
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* @invmsk: invert data mask (will be xored on data)
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*
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* The parity uses a uint16_t data type to enable
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* symbol size > 8. The calling code must take care of encoding of the
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* syndrome result for storage itself.
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*/
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int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
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uint16_t invmsk)
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{
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#include "encode_rs.c"
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}
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EXPORT_SYMBOL_GPL(encode_rs8);
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#endif
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#ifdef CONFIG_REED_SOLOMON_DEC8
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/**
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* decode_rs8 - Decode codeword (8bit data width)
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* @rs: the rs control structure
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* @data: data field of a given type
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* @par: received parity data field
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* @len: data length
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* @s: syndrome data field (if NULL, syndrome is calculated)
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* @no_eras: number of erasures
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* @eras_pos: position of erasures, can be NULL
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* @invmsk: invert data mask (will be xored on data, not on parity!)
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* @corr: buffer to store correction bitmask on eras_pos
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*
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* The syndrome and parity uses a uint16_t data type to enable
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* symbol size > 8. The calling code must take care of decoding of the
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* syndrome result and the received parity before calling this code.
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* Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
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*/
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int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
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uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
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uint16_t *corr)
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{
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#include "decode_rs.c"
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}
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EXPORT_SYMBOL_GPL(decode_rs8);
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#endif
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#ifdef CONFIG_REED_SOLOMON_ENC16
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/**
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* encode_rs16 - Calculate the parity for data values (16bit data width)
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* @rs: the rs control structure
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* @data: data field of a given type
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* @len: data length
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* @par: parity data, must be initialized by caller (usually all 0)
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* @invmsk: invert data mask (will be xored on data, not on parity!)
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*
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* Each field in the data array contains up to symbol size bits of valid data.
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*/
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int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
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uint16_t invmsk)
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{
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#include "encode_rs.c"
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}
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EXPORT_SYMBOL_GPL(encode_rs16);
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#endif
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#ifdef CONFIG_REED_SOLOMON_DEC16
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/**
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* decode_rs16 - Decode codeword (16bit data width)
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* @rs: the rs control structure
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* @data: data field of a given type
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* @par: received parity data field
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* @len: data length
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* @s: syndrome data field (if NULL, syndrome is calculated)
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* @no_eras: number of erasures
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* @eras_pos: position of erasures, can be NULL
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* @invmsk: invert data mask (will be xored on data, not on parity!)
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* @corr: buffer to store correction bitmask on eras_pos
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*
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* Each field in the data array contains up to symbol size bits of valid data.
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* Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
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*/
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int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
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uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
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uint16_t *corr)
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{
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#include "decode_rs.c"
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}
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EXPORT_SYMBOL_GPL(decode_rs16);
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#endif
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EXPORT_SYMBOL_GPL(init_rs);
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EXPORT_SYMBOL_GPL(init_rs_non_canonical);
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EXPORT_SYMBOL_GPL(free_rs);
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
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MODULE_AUTHOR("Phil Karn, Thomas Gleixner");
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