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/*
* Copyright (c) International Business Machines Corp., 2006
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
* the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* ECC algorithm for NAND FLASH. Detects and corrects 1 bit errors in
* a 256 bytes of data.
*
* Reimplement by Thomas Gleixner after staring long enough at the
* mess in drivers/mtd/nand/nandecc.c
*
*/
#include "nandecc.h"
static int countbits(uint32_t byte)
{
int res = 0;
for (;byte; byte >>= 1)
res += byte & 0x01;
return res;
}
int nand_correct_data(uint8_t *dat, const uint8_t *fail_ecc)
{
uint8_t s0, s1, s2;
/*
* Do error detection
*
* Be careful, the index magic is due to a pointer to a
* uint32_t.
*/
s0 = fail_ecc[1];
s1 = fail_ecc[2];
s2 = fail_ecc[3];
/* Check for a single bit error */
if( ((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {
uint32_t byteoffs, bitnum;
byteoffs = (s1 << 0) & 0x80;
byteoffs |= (s1 << 1) & 0x40;
byteoffs |= (s1 << 2) & 0x20;
byteoffs |= (s1 << 3) & 0x10;
byteoffs |= (s0 >> 4) & 0x08;
byteoffs |= (s0 >> 3) & 0x04;
byteoffs |= (s0 >> 2) & 0x02;
byteoffs |= (s0 >> 1) & 0x01;
bitnum = (s2 >> 5) & 0x04;
bitnum |= (s2 >> 4) & 0x02;
bitnum |= (s2 >> 3) & 0x01;
dat[byteoffs] ^= (1 << bitnum);
return 1;
}
if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1)
return 1;
return -1;
}
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