519 lines
14 KiB
C
519 lines
14 KiB
C
/*
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* This file contains an ECC algorithm from Toshiba that detects and
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* corrects 1 bit errors in a 256 byte block of data.
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*
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* drivers/mtd/nand/nand_ecc.c
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*
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* Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
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* Toshiba America Electronics Components, Inc.
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*
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* $Id: nand_ecc_rs.c,v 1.1.1.1 2008/12/15 11:39:21 wokes Exp $
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*
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* This file is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 or (at your option) any
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* later version.
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*
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* This file is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this file; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
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*
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* As a special exception, if other files instantiate templates or use
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* macros or inline functions from these files, or you compile these
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* files and link them with other works to produce a work based on these
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* files, these files do not by themselves cause the resulting work to be
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* covered by the GNU General Public License. However the source code for
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* these files must still be made available in accordance with section (3)
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* of the GNU General Public License.
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*
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* This exception does not invalidate any other reasons why a work based on
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* this file might be covered by the GNU General Public License.
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*/
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#include <common.h>
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#if (CONFIG_COMMANDS & CFG_CMD_NAND) && !defined(CFG_NAND_LEGACY)
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#include<linux/mtd/mtd.h>
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#include <linux/mtd/nand_ecc_rs.h>
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#define mm 10 /* RS code over GF(2**mm) - the size in bits of a symbol*/
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#define nn 1023 /* nn=2^mm -1 length of codeword */
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#define tt 4 /* number of errors that can be corrected */
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#define kk 1015 /* kk = number of information symbols kk = nn-2*tt */
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static char rs_initialized = 0;
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//typedef unsigned int gf;
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typedef u_short tgf; /* data type of Galois Functions */
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/* Primitive polynomials - irriducibile polynomial [ 1+x^3+x^10 ]*/
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short pp[mm+1] = { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1 };
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/* index->polynomial form conversion table */
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tgf alpha_to[nn + 1];
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/* Polynomial->index form conversion table */
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tgf index_of[nn + 1];
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/* Generator polynomial g(x) = 2*tt with roots @, @^2, .. ,@^(2*tt) */
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tgf Gg[nn - kk + 1];
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#define minimum(a,b) ((a) < (b) ? (a) : (b))
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#define BLANK(a,n) {\
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short ci;\
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for(ci=0; ci<(n); ci++)\
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(a)[ci] = 0;\
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}
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#define COPY(a,b,n) {\
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short ci;\
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for(ci=(n)-1;ci >=0;ci--)\
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(a)[ci] = (b)[ci];\
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}
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#define COPYDOWN(a,b,n) {\
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short ci;\
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for(ci=(n)-1;ci >=0;ci--)\
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(a)[ci] = (b)[ci];\
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}
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/* generate GF(2^m) from the irreducible polynomial p(X) in p[0]..p[mm]
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lookup tables: index->polynomial form alpha_to[] contains j=alpha^i;
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polynomial form -> index form index_of[j=alpha^i] = i
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alpha=2 is the primitive element of GF(2^m)
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*/
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void generate_gf(void)
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{
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register int i, mask;
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mask = 1;
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alpha_to[mm] = 0;
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for (i = 0; i < mm; i++) {
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alpha_to[i] = mask;
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index_of[alpha_to[i]] = i;
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if (pp[i] != 0)
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alpha_to[mm] ^= mask;
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mask <<= 1;
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}
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index_of[alpha_to[mm]] = mm;
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mask >>= 1;
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for (i = mm + 1; i < nn; i++) {
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if (alpha_to[i - 1] >= mask)
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alpha_to[i] = alpha_to[mm] ^ ((alpha_to[i - 1] ^ mask) << 1);
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else
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alpha_to[i] = alpha_to[i - 1] << 1;
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index_of[alpha_to[i]] = i;
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}
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index_of[0] = nn;
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alpha_to[nn] = 0;
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}
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/*
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* Obtain the generator polynomial of the tt-error correcting,
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* length nn = (2^mm -1)
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* Reed Solomon code from the product of (X + @^i), i=1..2*tt
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*/
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void gen_poly(void)
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{
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register int i, j;
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Gg[0] = alpha_to[1]; /* primitive element*/
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Gg[1] = 1; /* g(x) = (X+@^1) initially */
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for (i = 2; i <= nn - kk; i++) {
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Gg[i] = 1;
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/*
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* Below multiply (Gg[0]+Gg[1]*x + ... +Gg[i]x^i) by
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* (@^i + x)
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*/
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for (j = i - 1; j > 0; j--)
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if (Gg[j] != 0)
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Gg[j] = Gg[j - 1] ^ alpha_to[((index_of[Gg[j]]) + i)%nn];
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else
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Gg[j] = Gg[j - 1];
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Gg[0] = alpha_to[((index_of[Gg[0]]) + i) % nn];
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}
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/* convert Gg[] to index form for quicker encoding */
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for (i = 0; i <= nn - kk; i++)
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Gg[i] = index_of[Gg[i]];
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}
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/*
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* take the string of symbols in data[i], i=0..(k-1) and encode
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* systematically to produce nn-kk parity symbols in bb[0]..bb[nn-kk-1] data[]
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* is input and bb[] is output in polynomial form. Encoding is done by using
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* a feedback shift register with appropriate connections specified by the
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* elements of Gg[], which was generated above. Codeword is c(X) =
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* data(X)*X**(nn-kk)+ b(X)
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*/
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char encode_rs(dtype data[kk], dtype bb[nn-kk])
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{
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register int i, j;
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tgf feedback;
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BLANK(bb,nn-kk);
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for (i = kk - 1; i >= 0; i--) {
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if(data[i] > nn)
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return -1; /* Illegal symbol */
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feedback = index_of[data[i] ^ bb[nn - kk - 1]];
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if (feedback != nn) { /* feedback term is non-zero */
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for (j = nn - kk - 1; j > 0; j--)
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if (Gg[j] != nn)
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bb[j] = bb[j - 1] ^ alpha_to[(Gg[j] + feedback)%nn];
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else
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bb[j] = bb[j - 1];
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bb[0] = alpha_to[(Gg[0] + feedback)%nn];
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} else {
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for (j = nn - kk - 1; j > 0; j--)
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bb[j] = bb[j - 1];
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bb[0] = 0;
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}
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}
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return 0;
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}
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/* assume we have received bits grouped into mm-bit symbols in data[i],
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i=0..(nn-1), We first compute the 2*tt syndromes, then we use the
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Berlekamp iteration to find the error location polynomial elp[i].
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If the degree of the elp is >tt, we cannot correct all the errors
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and hence just put out the information symbols uncorrected. If the
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degree of elp is <=tt, we get the roots, hence the inverse roots,
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the error location numbers. If the number of errors located does not
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equal the degree of the elp, we have more than tt errors and cannot
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correct them. Otherwise, we then solve for the error value at the
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error location and correct the error.The procedure is that found in
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Lin and Costello.*/
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int decode_rs(dtype data[nn])
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{
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int deg_lambda, el, deg_omega;
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int i, j, r;
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tgf q,tmp,num1,num2,den,discr_r;
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tgf recd[nn];
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tgf lambda[nn-kk + 1], s[nn-kk + 1]; /* Err+Eras Locator poly
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* and syndrome poly */
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tgf b[nn-kk + 1], t[nn-kk + 1], omega[nn-kk + 1];
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tgf root[nn-kk], reg[nn-kk + 1], loc[nn-kk];
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int syn_error, count;
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/* data[] is in polynomial form, copy and convert to index form */
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for (i = nn-1; i >= 0; i--){
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if(data[i] > nn)
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return -1; /* Illegal symbol */
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recd[i] = index_of[data[i]];
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}
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/* first form the syndromes; i.e., evaluate recd(x) at roots of g(x)
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* namely @**(1+i), i = 0, ... ,(nn-kk-1)
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*/
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syn_error = 0;
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for (i = 1; i <= nn-kk; i++) {
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tmp = 0;
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for (j = 0; j < nn; j++)
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if (recd[j] != nn) /* recd[j] in index form */
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tmp ^= alpha_to[(recd[j] + (1+i-1)*j)%nn];
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syn_error |= tmp; /* set flag if non-zero syndrome =>
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* error */
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/* store syndrome in index form */
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s[i] = index_of[tmp];
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}
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if (!syn_error) {
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/*
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* if syndrome is zero, data[] is a codeword and there are no
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* errors to correct. So return data[] unmodified
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*/
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return 0;
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}
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BLANK(&lambda[1],nn-kk);
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lambda[0] = 1;
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for(i=0;i<nn-kk+1;i++)
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b[i] = index_of[lambda[i]];
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/*
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* Begin Berlekamp-Massey algorithm to determine error
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* locator polynomial
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*/
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r = 0;
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el = 0;
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while (++r <= nn-kk) { /* r is the step number */
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/* Compute discrepancy at the r-th step in poly-form */
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discr_r = 0;
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for (i = 0; i < r; i++){
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if ((lambda[i] != 0) && (s[r - i] != nn)) {
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discr_r ^= alpha_to[(index_of[lambda[i]] + s[r - i])%nn];
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}
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}
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discr_r = index_of[discr_r]; /* Index form */
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if (discr_r == nn) {
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/* 2 lines below: B(x) <-- x*B(x) */
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COPYDOWN(&b[1],b,nn-kk);
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b[0] = nn;
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} else {
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/* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */
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t[0] = lambda[0];
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for (i = 0 ; i < nn-kk; i++) {
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if(b[i] != nn)
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//t[i+1] = lambda[i+1] ^ alpha_to[modnn(discr_r + b[i])];
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t[i+1] = lambda[i+1] ^ alpha_to[(discr_r + b[i])%nn];
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else
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t[i+1] = lambda[i+1];
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}
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if (2 * el <= r - 1) {
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el = r - el;
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/*
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* 2 lines below: B(x) <-- inv(discr_r) *
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* lambda(x)
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*/
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for (i = 0; i <= nn-kk; i++)
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//b[i] = (lambda[i] == 0) ? nn : modnn(index_of[lambda[i]] - discr_r + nn);
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b[i] = (lambda[i] == 0) ? nn : ((index_of[lambda[i]] - discr_r + nn)%nn);
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} else {
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/* 2 lines below: B(x) <-- x*B(x) */
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COPYDOWN(&b[1],b,nn-kk);
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b[0] = nn;
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}
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COPY(lambda,t,nn-kk+1);
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}
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}
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/* Convert lambda to index form and compute deg(lambda(x)) */
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deg_lambda = 0;
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for(i=0;i<nn-kk+1;i++){
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lambda[i] = index_of[lambda[i]];
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if(lambda[i] != nn)
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deg_lambda = i;
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}
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/*
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* Find roots of the error locator polynomial. By Chien
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* Search
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*/
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COPY(®[1],&lambda[1],nn-kk);
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count = 0; /* Number of roots of lambda(x) */
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for (i = 1; i <= nn; i++) {
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q = 1;
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for (j = deg_lambda; j > 0; j--)
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if (reg[j] != nn) {
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//reg[j] = modnn(reg[j] + j);
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reg[j] = (reg[j] + j)%nn;
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q ^= alpha_to[reg[j]];
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}
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if (!q) {
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/* store root (index-form) and error location number */
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root[count] = i;
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loc[count] = nn - i;
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count++;
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}
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}
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#ifdef DEBUG
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/*
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printf("\n Final error positions:\t");
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for (i = 0; i < count; i++)
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printf("%d ", loc[i]);
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printf("\n");
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*/
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#endif
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if (deg_lambda != count) {
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/*
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* deg(lambda) unequal to number of roots => uncorrectable
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* error detected
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*/
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return -1;
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}
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/*
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* Compute err evaluator poly omega(x) = s(x)*lambda(x) (modulo
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* x**(nn-kk)). in index form. Also find deg(omega).
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*/
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deg_omega = 0;
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for (i = 0; i < nn-kk;i++){
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tmp = 0;
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j = (deg_lambda < i) ? deg_lambda : i;
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for(;j >= 0; j--){
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if ((s[i + 1 - j] != nn) && (lambda[j] != nn))
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//tmp ^= alpha_to[modnn(s[i + 1 - j] + lambda[j])];
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tmp ^= alpha_to[(s[i + 1 - j] + lambda[j])%nn];
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}
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if(tmp != 0)
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deg_omega = i;
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omega[i] = index_of[tmp];
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}
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omega[nn-kk] = nn;
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/*
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* Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
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* inv(X(l))**(1-1) and den = lambda_pr(inv(X(l))) all in poly-form
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*/
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for (j = count-1; j >=0; j--) {
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num1 = 0;
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for (i = deg_omega; i >= 0; i--) {
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if (omega[i] != nn)
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//num1 ^= alpha_to[modnn(omega[i] + i * root[j])];
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num1 ^= alpha_to[(omega[i] + i * root[j])%nn];
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}
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//num2 = alpha_to[modnn(root[j] * (1 - 1) + nn)];
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num2 = alpha_to[(root[j] * (1 - 1) + nn)%nn];
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den = 0;
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/* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */
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for (i = minimum(deg_lambda,nn-kk-1) & ~1; i >= 0; i -=2) {
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if(lambda[i+1] != nn)
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//den ^= alpha_to[modnn(lambda[i+1] + i * root[j])];
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den ^= alpha_to[(lambda[i+1] + i * root[j])%nn];
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}
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if (den == 0) {
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#ifdef DEBUG
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printf("\n ERROR: denominator = 0\n");
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#endif
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return -1;
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}
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/* Apply error to data */
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if (num1 != 0) {
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//data[loc[j]] ^= alpha_to[modnn(index_of[num1] + index_of[num2] + nn - index_of[den])];
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data[loc[j]] ^= alpha_to[(index_of[num1] + index_of[num2] + nn - index_of[den])%nn];
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}
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}
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return count;
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}
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/**
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* nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
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* @mtd: MTD block structure
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* @dat: raw data
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* @ecc_code: buffer for ECC
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*/
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int nand_calculate_ecc_rs(struct mtd_info *mtd, const u_char *data, u_char *ecc_code)
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{
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int i,j;
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u_short rsdata[nn];
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/* Generate Tables in first run */
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if (!rs_initialized) {
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generate_gf();
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gen_poly();
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rs_initialized = 1;
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}
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for(i=512; i<nn; i++)
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rsdata[i] = 0;
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for (j=0; j<4; j++)
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{
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for(i=0; i<512; i++)
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rsdata[i] = (u_short) data[i+(j*512)];
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if ((encode_rs(rsdata,&(rsdata[kk]))) != 0)
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return -1;
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*(ecc_code+(j*10)) = (unsigned char) rsdata[kk];
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*(ecc_code+1+(j*10)) = ((rsdata[0x3F7]) >> 8) | ((rsdata[0x3F7+1]) << 2);
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*(ecc_code+2+(j*10)) = ((rsdata[0x3F7+1]) >> 6) | ((rsdata[0x3F7+2]) << 4);
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*(ecc_code+3+(j*10)) = ((rsdata[0x3F7+2]) >> 4) | ((rsdata[0x3F7+3]) << 6);
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*(ecc_code+4+(j*10)) = ((rsdata[0x3F7+3]) >> 2);
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*(ecc_code+5+(j*10)) = (unsigned char) rsdata[kk+4];
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*(ecc_code+6+(j*10)) = ((rsdata[0x3F7+4]) >> 8) | ((rsdata[0x3F7+1+4]) << 2);
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*(ecc_code+7+(j*10)) = ((rsdata[0x3F7+1+4]) >> 6) | ((rsdata[0x3F7+2+4]) << 4);
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*(ecc_code+8+(j*10)) = ((rsdata[0x3F7+2+4]) >> 4) | ((rsdata[0x3F7+3+4]) << 6);
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*(ecc_code+9+(j*10)) = ((rsdata[0x3F7+3+4]) >> 2);
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}
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return 0;
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}
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/**
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* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
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* @mtd: MTD block structure
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* @dat: raw data read from the chip
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* @store_ecc: ECC from the chip
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* @calc_ecc: the ECC calculated from raw data
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*
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* Detect and correct a 1 bit error for 256 byte block
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*/
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int nand_correct_data_rs(struct mtd_info *mtd, u_char *data, u_char *store_ecc, u_char *calc_ecc)
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{
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int ret,i,j;
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u_short rsdata[nn];
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/* Generate Tables in first run */
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if (!rs_initialized) {
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generate_gf();
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gen_poly();
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rs_initialized = 1;
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}
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for(i=512; i<nn; i++) rsdata[i] = 0;
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/* errors*/
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//data[20] = 0xDD;
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//data[30] = 0xDD;
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//data[40] = 0xDD;
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//data[50] = 0xDD;
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//data[60] = 0xDD;
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/* Ecc is calculated on chunks of 512B */
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for (j=0; j<4; j++)
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{
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for(i=0; i<512; i++)
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rsdata[i] = (u_short) data[i+(j*512)];
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rsdata[kk] = ( (*(store_ecc+1+(j*10)) & 0x03) <<8) | (*(store_ecc+(j*10)));
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rsdata[kk+1] = ( (*(store_ecc+2+(j*10)) & 0x0F) <<6) | (*(store_ecc+1+(j*10))>>2);
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rsdata[kk+2] = ( (*(store_ecc+3+(j*10)) & 0x3F) <<4) | (*(store_ecc+2+(j*10))>>4);
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rsdata[kk+3] = (*(store_ecc+4+(j*10)) <<2) | (*(store_ecc+3+(j*10))>>6);
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rsdata[kk+4] = ( (*(store_ecc+1+5+(j*10)) & 0x03) <<8) | (*(store_ecc+5+(j*10)));
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rsdata[kk+5] = ( (*(store_ecc+2+5+(j*10)) & 0x0F) <<6) | (*(store_ecc+1+5+(j*10))>>2);
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rsdata[kk+6] = ( (*(store_ecc+3+5+(j*10)) & 0x3F) <<4) | (*(store_ecc+2+5+(j*10))>>4);
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rsdata[kk+7] = (*(store_ecc+4+5+(j*10)) <<2) | (*(store_ecc+3+5+(j*10))>>6);
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ret = decode_rs(rsdata);
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/* Check for excessive errors */
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if ((ret > tt) || (ret < 0))
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return -1;
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/* Copy corrected data */
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for (i=0; i<512; i++)
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data[i+(j*512)] = (unsigned char) rsdata[i];
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}
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return 0;
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}
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#endif /* CONFIG_COMMANDS & CFG_CMD_NAND */
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