59018b6d2a
Once upon a time, the MTD repository was using CVS. This patch therefore removes all usages of the no longer updated CVS keywords from the MTD code. This also includes code that printed them to the user. Signed-off-by: Adrian Bunk <bunk@kernel.org> Signed-off-by: David Woodhouse <dwmw2@infradead.org>
523 lines
16 KiB
C
523 lines
16 KiB
C
/*
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* ECC algorithm for M-systems disk on chip. We use the excellent Reed
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* Solmon code of Phil Karn (karn@ka9q.ampr.org) available under the
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* GNU GPL License. The rest is simply to convert the disk on chip
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* syndrom into a standard syndom.
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*
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* Author: Fabrice Bellard (fabrice.bellard@netgem.com)
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* Copyright (C) 2000 Netgem S.A.
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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 as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <asm/errno.h>
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#include <asm/io.h>
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#include <asm/uaccess.h>
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#include <linux/miscdevice.h>
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#include <linux/delay.h>
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#include <linux/slab.h>
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#include <linux/init.h>
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#include <linux/types.h>
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#include <linux/mtd/compatmac.h> /* for min() in older kernels */
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#include <linux/mtd/mtd.h>
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#include <linux/mtd/doc2000.h>
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#define DEBUG_ECC 0
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/* need to undef it (from asm/termbits.h) */
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#undef B0
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#define MM 10 /* Symbol size in bits */
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#define KK (1023-4) /* Number of data symbols per block */
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#define B0 510 /* First root of generator polynomial, alpha form */
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#define PRIM 1 /* power of alpha used to generate roots of generator poly */
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#define NN ((1 << MM) - 1)
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typedef unsigned short dtype;
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/* 1+x^3+x^10 */
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static const int Pp[MM+1] = { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1 };
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/* This defines the type used to store an element of the Galois Field
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* used by the code. Make sure this is something larger than a char if
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* if anything larger than GF(256) is used.
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*
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* Note: unsigned char will work up to GF(256) but int seems to run
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* faster on the Pentium.
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*/
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typedef int gf;
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/* No legal value in index form represents zero, so
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* we need a special value for this purpose
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*/
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#define A0 (NN)
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/* Compute x % NN, where NN is 2**MM - 1,
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* without a slow divide
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*/
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static inline gf
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modnn(int x)
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{
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while (x >= NN) {
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x -= NN;
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x = (x >> MM) + (x & NN);
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}
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return x;
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}
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#define CLEAR(a,n) {\
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int ci;\
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for(ci=(n)-1;ci >=0;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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int 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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int 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 Ldec 1
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/* generate GF(2**m) from the irreducible polynomial p(X) in Pp[0]..Pp[m]
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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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HARI's COMMENT: (4/13/94) alpha_to[] can be used as follows:
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Let @ represent the primitive element commonly called "alpha" that
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is the root of the primitive polynomial p(x). Then in GF(2^m), for any
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0 <= i <= 2^m-2,
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@^i = a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1)
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where the binary vector (a(0),a(1),a(2),...,a(m-1)) is the representation
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of the integer "alpha_to[i]" with a(0) being the LSB and a(m-1) the MSB. Thus for
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example the polynomial representation of @^5 would be given by the binary
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representation of the integer "alpha_to[5]".
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Similarily, index_of[] can be used as follows:
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As above, let @ represent the primitive element of GF(2^m) that is
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the root of the primitive polynomial p(x). In order to find the power
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of @ (alpha) that has the polynomial representation
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a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1)
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we consider the integer "i" whose binary representation with a(0) being LSB
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and a(m-1) MSB is (a(0),a(1),...,a(m-1)) and locate the entry
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"index_of[i]". Now, @^index_of[i] is that element whose polynomial
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representation is (a(0),a(1),a(2),...,a(m-1)).
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NOTE:
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The element alpha_to[2^m-1] = 0 always signifying that the
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representation of "@^infinity" = 0 is (0,0,0,...,0).
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Similarily, the element index_of[0] = A0 always signifying
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that the power of alpha which has the polynomial representation
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(0,0,...,0) is "infinity".
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*/
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static void
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generate_gf(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1])
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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] == 1 then, term @^i occurs in poly-repr of @^MM */
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if (Pp[i] != 0)
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Alpha_to[MM] ^= mask; /* Bit-wise EXOR operation */
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mask <<= 1; /* single left-shift */
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}
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Index_of[Alpha_to[MM]] = MM;
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/*
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* Have obtained poly-repr of @^MM. Poly-repr of @^(i+1) is given by
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* poly-repr of @^i shifted left one-bit and accounting for any @^MM
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* term that may occur when poly-repr of @^i is shifted.
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*/
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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] = A0;
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Alpha_to[NN] = 0;
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}
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/*
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* Performs ERRORS+ERASURES decoding of RS codes. bb[] is the content
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* of the feedback shift register after having processed the data and
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* the ECC.
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*
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* Return number of symbols corrected, or -1 if codeword is illegal
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* or uncorrectable. If eras_pos is non-null, the detected error locations
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* are written back. NOTE! This array must be at least NN-KK elements long.
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* The corrected data are written in eras_val[]. They must be xor with the data
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* to retrieve the correct data : data[erase_pos[i]] ^= erase_val[i] .
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*
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* First "no_eras" erasures are declared by the calling program. Then, the
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* maximum # of errors correctable is t_after_eras = floor((NN-KK-no_eras)/2).
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* If the number of channel errors is not greater than "t_after_eras" the
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* transmitted codeword will be recovered. Details of algorithm can be found
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* in R. Blahut's "Theory ... of Error-Correcting Codes".
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* Warning: the eras_pos[] array must not contain duplicate entries; decoder failure
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* will result. The decoder *could* check for this condition, but it would involve
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* extra time on every decoding operation.
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* */
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static int
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eras_dec_rs(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1],
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gf bb[NN - KK + 1], gf eras_val[NN-KK], int eras_pos[NN-KK],
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int no_eras)
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{
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int deg_lambda, el, deg_omega;
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int i, j, r,k;
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gf u,q,tmp,num1,num2,den,discr_r;
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gf lambda[NN-KK + 1], s[NN-KK + 1]; /* Err+Eras Locator poly
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* and syndrome poly */
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gf b[NN-KK + 1], t[NN-KK + 1], omega[NN-KK + 1];
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gf root[NN-KK], reg[NN-KK + 1], loc[NN-KK];
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int syn_error, count;
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syn_error = 0;
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for(i=0;i<NN-KK;i++)
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syn_error |= bb[i];
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if (!syn_error) {
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/* if remainder 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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count = 0;
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goto finish;
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}
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for(i=1;i<=NN-KK;i++){
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s[i] = bb[0];
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}
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for(j=1;j<NN-KK;j++){
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if(bb[j] == 0)
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continue;
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tmp = Index_of[bb[j]];
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for(i=1;i<=NN-KK;i++)
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s[i] ^= Alpha_to[modnn(tmp + (B0+i-1)*PRIM*j)];
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}
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/* undo the feedback register implicit multiplication and convert
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syndromes to index form */
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for(i=1;i<=NN-KK;i++) {
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tmp = Index_of[s[i]];
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if (tmp != A0)
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tmp = modnn(tmp + 2 * KK * (B0+i-1)*PRIM);
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s[i] = tmp;
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}
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CLEAR(&lambda[1],NN-KK);
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lambda[0] = 1;
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if (no_eras > 0) {
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/* Init lambda to be the erasure locator polynomial */
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lambda[1] = Alpha_to[modnn(PRIM * eras_pos[0])];
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for (i = 1; i < no_eras; i++) {
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u = modnn(PRIM*eras_pos[i]);
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for (j = i+1; j > 0; j--) {
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tmp = Index_of[lambda[j - 1]];
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if(tmp != A0)
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lambda[j] ^= Alpha_to[modnn(u + tmp)];
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}
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}
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#if DEBUG_ECC >= 1
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/* Test code that verifies the erasure locator polynomial just constructed
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Needed only for decoder debugging. */
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/* find roots of the erasure location polynomial */
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for(i=1;i<=no_eras;i++)
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reg[i] = Index_of[lambda[i]];
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count = 0;
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for (i = 1,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) {
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q = 1;
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for (j = 1; j <= no_eras; j++)
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if (reg[j] != A0) {
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reg[j] = modnn(reg[j] + j);
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q ^= Alpha_to[reg[j]];
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}
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if (q != 0)
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continue;
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/* store root and error location number indices */
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root[count] = i;
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loc[count] = k;
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count++;
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}
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if (count != no_eras) {
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printf("\n lambda(x) is WRONG\n");
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count = -1;
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goto finish;
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}
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#if DEBUG_ECC >= 2
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printf("\n Erasure positions as determined by roots of Eras Loc Poly:\n");
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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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#endif
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#endif
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}
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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+erasure
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* locator polynomial
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*/
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r = no_eras;
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el = no_eras;
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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] != A0)) {
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discr_r ^= Alpha_to[modnn(Index_of[lambda[i]] + s[r - i])];
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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 == A0) {
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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] = A0;
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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] != A0)
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t[i+1] = lambda[i+1] ^ Alpha_to[modnn(discr_r + b[i])];
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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 + no_eras - 1) {
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el = r + no_eras - 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) ? A0 : modnn(Index_of[lambda[i]] - discr_r + 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] = A0;
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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] != A0)
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deg_lambda = i;
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}
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/*
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* Find roots of the error+erasure 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,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) {
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q = 1;
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for (j = deg_lambda; j > 0; j--){
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if (reg[j] != A0) {
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reg[j] = modnn(reg[j] + j);
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q ^= Alpha_to[reg[j]];
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}
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}
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if (q != 0)
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continue;
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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] = k;
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/* If we've already found max possible roots,
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* abort the search to save time
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*/
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if(++count == deg_lambda)
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break;
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}
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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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count = -1;
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goto finish;
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}
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/*
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* Compute err+eras 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] != A0) && (lambda[j] != A0))
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tmp ^= Alpha_to[modnn(s[i + 1 - j] + lambda[j])];
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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] = A0;
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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))**(B0-1) 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] != A0)
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num1 ^= Alpha_to[modnn(omega[i] + i * root[j])];
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}
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num2 = Alpha_to[modnn(root[j] * (B0 - 1) + 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 = min(deg_lambda,NN-KK-1) & ~1; i >= 0; i -=2) {
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if(lambda[i+1] != A0)
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den ^= Alpha_to[modnn(lambda[i+1] + i * root[j])];
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}
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if (den == 0) {
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#if DEBUG_ECC >= 1
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printf("\n ERROR: denominator = 0\n");
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#endif
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/* Convert to dual- basis */
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count = -1;
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goto finish;
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}
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/* Apply error to data */
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if (num1 != 0) {
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eras_val[j] = Alpha_to[modnn(Index_of[num1] + Index_of[num2] + NN - Index_of[den])];
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} else {
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eras_val[j] = 0;
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}
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}
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finish:
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for(i=0;i<count;i++)
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eras_pos[i] = loc[i];
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return count;
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}
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/***************************************************************************/
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/* The DOC specific code begins here */
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#define SECTOR_SIZE 512
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/* The sector bytes are packed into NB_DATA MM bits words */
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#define NB_DATA (((SECTOR_SIZE + 1) * 8 + 6) / MM)
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/*
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* Correct the errors in 'sector[]' by using 'ecc1[]' which is the
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* content of the feedback shift register applyied to the sector and
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* the ECC. Return the number of errors corrected (and correct them in
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* sector), or -1 if error
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*/
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int doc_decode_ecc(unsigned char sector[SECTOR_SIZE], unsigned char ecc1[6])
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{
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int parity, i, nb_errors;
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gf bb[NN - KK + 1];
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gf error_val[NN-KK];
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int error_pos[NN-KK], pos, bitpos, index, val;
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dtype *Alpha_to, *Index_of;
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/* init log and exp tables here to save memory. However, it is slower */
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Alpha_to = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL);
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if (!Alpha_to)
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return -1;
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Index_of = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL);
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if (!Index_of) {
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kfree(Alpha_to);
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return -1;
|
|
}
|
|
|
|
generate_gf(Alpha_to, Index_of);
|
|
|
|
parity = ecc1[1];
|
|
|
|
bb[0] = (ecc1[4] & 0xff) | ((ecc1[5] & 0x03) << 8);
|
|
bb[1] = ((ecc1[5] & 0xfc) >> 2) | ((ecc1[2] & 0x0f) << 6);
|
|
bb[2] = ((ecc1[2] & 0xf0) >> 4) | ((ecc1[3] & 0x3f) << 4);
|
|
bb[3] = ((ecc1[3] & 0xc0) >> 6) | ((ecc1[0] & 0xff) << 2);
|
|
|
|
nb_errors = eras_dec_rs(Alpha_to, Index_of, bb,
|
|
error_val, error_pos, 0);
|
|
if (nb_errors <= 0)
|
|
goto the_end;
|
|
|
|
/* correct the errors */
|
|
for(i=0;i<nb_errors;i++) {
|
|
pos = error_pos[i];
|
|
if (pos >= NB_DATA && pos < KK) {
|
|
nb_errors = -1;
|
|
goto the_end;
|
|
}
|
|
if (pos < NB_DATA) {
|
|
/* extract bit position (MSB first) */
|
|
pos = 10 * (NB_DATA - 1 - pos) - 6;
|
|
/* now correct the following 10 bits. At most two bytes
|
|
can be modified since pos is even */
|
|
index = (pos >> 3) ^ 1;
|
|
bitpos = pos & 7;
|
|
if ((index >= 0 && index < SECTOR_SIZE) ||
|
|
index == (SECTOR_SIZE + 1)) {
|
|
val = error_val[i] >> (2 + bitpos);
|
|
parity ^= val;
|
|
if (index < SECTOR_SIZE)
|
|
sector[index] ^= val;
|
|
}
|
|
index = ((pos >> 3) + 1) ^ 1;
|
|
bitpos = (bitpos + 10) & 7;
|
|
if (bitpos == 0)
|
|
bitpos = 8;
|
|
if ((index >= 0 && index < SECTOR_SIZE) ||
|
|
index == (SECTOR_SIZE + 1)) {
|
|
val = error_val[i] << (8 - bitpos);
|
|
parity ^= val;
|
|
if (index < SECTOR_SIZE)
|
|
sector[index] ^= val;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* use parity to test extra errors */
|
|
if ((parity & 0xff) != 0)
|
|
nb_errors = -1;
|
|
|
|
the_end:
|
|
kfree(Alpha_to);
|
|
kfree(Index_of);
|
|
return nb_errors;
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(doc_decode_ecc);
|
|
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_AUTHOR("Fabrice Bellard <fabrice.bellard@netgem.com>");
|
|
MODULE_DESCRIPTION("ECC code for correcting errors detected by DiskOnChip 2000 and Millennium ECC hardware");
|