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/*
* $Id: ecc.c,v 1.6 2003/06/12 08:32:33 germeier Exp $
*
* libmpio - a library for accessing Digit@lways MPIO players
* Copyright (C) 2002, 2003 Markus Germeier
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc.,g 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include "ecc.h"
#include "debug.h"
#define GET_BIT(d, o) (((d) >> (o)) & 0x01 )
#define XOR_BITS(d, x1, x2, x3, x4) (GET_BIT((d), (x1)) ^ \
GET_BIT((d), (x2)) ^ \
GET_BIT((d), (x3)) ^ \
GET_BIT((d), (x4)))
#define ADD_BITS(c, d1, d2, v) if ((c)) d1 ^= (v); else d2 ^= (v)
int
mpio_ecc_256_gen(BYTE *data, BYTE *ecc)
{
BYTE p1, p1_;
BYTE p2, p2_;
BYTE p4, p4_;
BYTE p08, p08_;
BYTE p16, p16_;
BYTE p32, p32_;
BYTE p64, p64_;
BYTE p0128, p0128_;
BYTE p0256, p0256_;
BYTE p0512, p0512_;
BYTE p1024, p1024_;
int i, j;
/* init */
p1=p1_=0;
p2=p2_=0;
p4=p4_=0;
p08=p08_=0;
p16=p16_=0;
p32=p32_=0;
p64=p64_=0;
p0128=p0128_=0;
p0256=p0256_=0;
p0512=p0512_=0;
p1024=p1024_=0;
/* vertical */
for (i=0; i<256; i++) {
/* p1, p1_ */
p1 ^= XOR_BITS(data[i], 7, 5, 3, 1);
p1_^= XOR_BITS(data[i], 6, 4, 2, 0);
/* p2, p2_ */
p2 ^= XOR_BITS(data[i], 7, 6, 3, 2);
p2_^= XOR_BITS(data[i], 5, 4, 1, 0);
/* p4, p4_ */
p4 ^= XOR_BITS(data[i], 7, 6, 5, 4);
p4_^= XOR_BITS(data[i], 3, 2, 1, 0);
}
/* horizontal */
for (i=0; i<8; i++) {
for (j=0; j<256; j++) {
/* p08, p08_ */
ADD_BITS(GET_BIT(j, 0), p08, p08_, GET_BIT(data[j], i));
/* p16, p16_ */
ADD_BITS(GET_BIT(j, 1), p16, p16_, GET_BIT(data[j], i));
/* p32, p32_ */
ADD_BITS(GET_BIT(j, 2), p32, p32_, GET_BIT(data[j], i));
/* p64, p64_ */
ADD_BITS(GET_BIT(j, 3), p64, p64_, GET_BIT(data[j], i));
/* p0128, p0128_ */
ADD_BITS(GET_BIT(j, 4), p0128, p0128_, GET_BIT(data[j], i));
/* p0256, p0256_ */
ADD_BITS(GET_BIT(j, 5), p0256, p0256_, GET_BIT(data[j], i));
/* p0512, p0512_ */
ADD_BITS(GET_BIT(j, 6), p0512, p0512_, GET_BIT(data[j], i));
/* p1024, p1024_ */
ADD_BITS(GET_BIT(j, 7), p1024, p1024_, GET_BIT(data[j], i));
}
}
/* calculate actual ECC */
ecc[0]=~((p64 << 7) | (p64_ << 6) |
(p32 << 5) | (p32_ << 4) |
(p16 << 3) | (p16_ << 2) |
(p08 << 1) | (p08_ << 0));
ecc[1]=~((p1024 << 7) | (p1024_ << 6) |
(p0512 << 5) | (p0512_ << 4) |
(p0256 << 3) | (p0256_ << 2) |
(p0128 << 1) | (p0128_ << 0));
ecc[2]=~((p4 << 7) | (p4_ << 6) |
(p2 << 5) | (p2_ << 4) |
(p1 << 3) | (p1_ << 2));
return 0;
}
int
mpio_ecc_256_check(BYTE *data, BYTE *ecc)
{
BYTE own_ecc[3];
BYTE check[3];
BYTE line, col;
int v, i;
mpio_ecc_256_gen(data, own_ecc);
check[0] = (ecc[0] ^ own_ecc[0]);
check[1] = (ecc[1] ^ own_ecc[1]);
check[2] = (ecc[2] ^ own_ecc[2]);
/* if ECC is wrong, try to fix one-bit errors */
if (check[0] | check[1] | check[2]) {
debugn(3, "ECC %2x %2x %2x vs. %2x %2x %2x\n",
ecc[0], ecc[1], ecc[2], own_ecc[0], own_ecc[1], own_ecc[2]);
v=1;
for(i=0; i<4; i++)
{
if (!( (GET_BIT(check[1], i*2) ^
(GET_BIT(check[1], i*2+1)))))
v=0;
if (!( (GET_BIT(check[0], i*2) ^
(GET_BIT(check[0], i*2+1)))))
v=0;
}
for(i=1; i<4; i++)
{
if (!( (GET_BIT(check[2], i*2) ^
(GET_BIT(check[2], i*2+1)))))
v=0;
}
if (v) {
debugn(2, "correctable error detected ... fixing the bit\n");
line =
GET_BIT(check[1], 7) * 128 +
GET_BIT(check[1], 5) * 64 +
GET_BIT(check[1], 3) * 32 +
GET_BIT(check[1], 1) * 16 +
GET_BIT(check[0], 7) * 8 +
GET_BIT(check[0], 5) * 4 +
GET_BIT(check[0], 3) * 2 +
GET_BIT(check[0], 1);
col =
GET_BIT(check[2], 7) * 4 +
GET_BIT(check[2], 5) * 2 +
GET_BIT(check[2], 3);
debugn(3, "error in line: %d , col %d (byte is: %02x)\n",
line, col, data[line]);
data[line] ^= ( 1 << col);
debugn(3, "fixed byte is: %02x\n", data[line]);
} else {
debugn(2, "uncorrectable error detected. Sorry, you lose!\n");
return 1;
}
}
return 0;
}
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