diff options
Diffstat (limited to 'drivers/char/ftape/lowlevel/ftape-ecc.c')
| -rw-r--r-- | drivers/char/ftape/lowlevel/ftape-ecc.c | 853 |
1 files changed, 0 insertions, 853 deletions
diff --git a/drivers/char/ftape/lowlevel/ftape-ecc.c b/drivers/char/ftape/lowlevel/ftape-ecc.c deleted file mode 100644 index e5632f6..0000000 --- a/drivers/char/ftape/lowlevel/ftape-ecc.c +++ /dev/null @@ -1,853 +0,0 @@ -/* - * - * Copyright (c) 1993 Ning and David Mosberger. - - This is based on code originally written by Bas Laarhoven (bas@vimec.nl) - and David L. Brown, Jr., and incorporates improvements suggested by - Kai Harrekilde-Petersen. - - 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, 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; see the file COPYING. If not, write to - the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, - USA. - - * - * $Source: /homes/cvs/ftape-stacked/ftape/lowlevel/ftape-ecc.c,v $ - * $Revision: 1.3 $ - * $Date: 1997/10/05 19:18:10 $ - * - * This file contains the Reed-Solomon error correction code - * for the QIC-40/80 floppy-tape driver for Linux. - */ - -#include <linux/ftape.h> - -#include "../lowlevel/ftape-tracing.h" -#include "../lowlevel/ftape-ecc.h" - -/* Machines that are big-endian should define macro BIG_ENDIAN. - * Unfortunately, there doesn't appear to be a standard include file - * that works for all OSs. - */ - -#if defined(__sparc__) || defined(__hppa) -#define BIG_ENDIAN -#endif /* __sparc__ || __hppa */ - -#if defined(__mips__) -#error Find a smart way to determine the Endianness of the MIPS CPU -#endif - -/* Notice: to minimize the potential for confusion, we use r to - * denote the independent variable of the polynomials in the - * Galois Field GF(2^8). We reserve x for polynomials that - * that have coefficients in GF(2^8). - * - * The Galois Field in which coefficient arithmetic is performed are - * the polynomials over Z_2 (i.e., 0 and 1) modulo the irreducible - * polynomial f(r), where f(r)=r^8 + r^7 + r^2 + r + 1. A polynomial - * is represented as a byte with the MSB as the coefficient of r^7 and - * the LSB as the coefficient of r^0. For example, the binary - * representation of f(x) is 0x187 (of course, this doesn't fit into 8 - * bits). In this field, the polynomial r is a primitive element. - * That is, r^i with i in 0,...,255 enumerates all elements in the - * field. - * - * The generator polynomial for the QIC-80 ECC is - * - * g(x) = x^3 + r^105*x^2 + r^105*x + 1 - * - * which can be factored into: - * - * g(x) = (x-r^-1)(x-r^0)(x-r^1) - * - * the byte representation of the coefficients are: - * - * r^105 = 0xc0 - * r^-1 = 0xc3 - * r^0 = 0x01 - * r^1 = 0x02 - * - * Notice that r^-1 = r^254 as exponent arithmetic is performed - * modulo 2^8-1 = 255. - * - * For more information on Galois Fields and Reed-Solomon codes, refer - * to any good book. I found _An Introduction to Error Correcting - * Codes with Applications_ by S. A. Vanstone and P. C. van Oorschot - * to be a good introduction into the former. _CODING THEORY: The - * Essentials_ I found very useful for its concise description of - * Reed-Solomon encoding/decoding. - * - */ - -typedef __u8 Matrix[3][3]; - -/* - * gfpow[] is defined such that gfpow[i] returns r^i if - * i is in the range [0..255]. - */ -static const __u8 gfpow[] = -{ - 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, - 0x87, 0x89, 0x95, 0xad, 0xdd, 0x3d, 0x7a, 0xf4, - 0x6f, 0xde, 0x3b, 0x76, 0xec, 0x5f, 0xbe, 0xfb, - 0x71, 0xe2, 0x43, 0x86, 0x8b, 0x91, 0xa5, 0xcd, - 0x1d, 0x3a, 0x74, 0xe8, 0x57, 0xae, 0xdb, 0x31, - 0x62, 0xc4, 0x0f, 0x1e, 0x3c, 0x78, 0xf0, 0x67, - 0xce, 0x1b, 0x36, 0x6c, 0xd8, 0x37, 0x6e, 0xdc, - 0x3f, 0x7e, 0xfc, 0x7f, 0xfe, 0x7b, 0xf6, 0x6b, - 0xd6, 0x2b, 0x56, 0xac, 0xdf, 0x39, 0x72, 0xe4, - 0x4f, 0x9e, 0xbb, 0xf1, 0x65, 0xca, 0x13, 0x26, - 0x4c, 0x98, 0xb7, 0xe9, 0x55, 0xaa, 0xd3, 0x21, - 0x42, 0x84, 0x8f, 0x99, 0xb5, 0xed, 0x5d, 0xba, - 0xf3, 0x61, 0xc2, 0x03, 0x06, 0x0c, 0x18, 0x30, - 0x60, 0xc0, 0x07, 0x0e, 0x1c, 0x38, 0x70, 0xe0, - 0x47, 0x8e, 0x9b, 0xb1, 0xe5, 0x4d, 0x9a, 0xb3, - 0xe1, 0x45, 0x8a, 0x93, 0xa1, 0xc5, 0x0d, 0x1a, - 0x34, 0x68, 0xd0, 0x27, 0x4e, 0x9c, 0xbf, 0xf9, - 0x75, 0xea, 0x53, 0xa6, 0xcb, 0x11, 0x22, 0x44, - 0x88, 0x97, 0xa9, 0xd5, 0x2d, 0x5a, 0xb4, 0xef, - 0x59, 0xb2, 0xe3, 0x41, 0x82, 0x83, 0x81, 0x85, - 0x8d, 0x9d, 0xbd, 0xfd, 0x7d, 0xfa, 0x73, 0xe6, - 0x4b, 0x96, 0xab, 0xd1, 0x25, 0x4a, 0x94, 0xaf, - 0xd9, 0x35, 0x6a, 0xd4, 0x2f, 0x5e, 0xbc, 0xff, - 0x79, 0xf2, 0x63, 0xc6, 0x0b, 0x16, 0x2c, 0x58, - 0xb0, 0xe7, 0x49, 0x92, 0xa3, 0xc1, 0x05, 0x0a, - 0x14, 0x28, 0x50, 0xa0, 0xc7, 0x09, 0x12, 0x24, - 0x48, 0x90, 0xa7, 0xc9, 0x15, 0x2a, 0x54, 0xa8, - 0xd7, 0x29, 0x52, 0xa4, 0xcf, 0x19, 0x32, 0x64, - 0xc8, 0x17, 0x2e, 0x5c, 0xb8, 0xf7, 0x69, 0xd2, - 0x23, 0x46, 0x8c, 0x9f, 0xb9, 0xf5, 0x6d, 0xda, - 0x33, 0x66, 0xcc, 0x1f, 0x3e, 0x7c, 0xf8, 0x77, - 0xee, 0x5b, 0xb6, 0xeb, 0x51, 0xa2, 0xc3, 0x01 -}; - -/* - * This is a log table. That is, gflog[r^i] returns i (modulo f(r)). - * gflog[0] is undefined and the first element is therefore not valid. - */ -static const __u8 gflog[256] = -{ - 0xff, 0x00, 0x01, 0x63, 0x02, 0xc6, 0x64, 0x6a, - 0x03, 0xcd, 0xc7, 0xbc, 0x65, 0x7e, 0x6b, 0x2a, - 0x04, 0x8d, 0xce, 0x4e, 0xc8, 0xd4, 0xbd, 0xe1, - 0x66, 0xdd, 0x7f, 0x31, 0x6c, 0x20, 0x2b, 0xf3, - 0x05, 0x57, 0x8e, 0xe8, 0xcf, 0xac, 0x4f, 0x83, - 0xc9, 0xd9, 0xd5, 0x41, 0xbe, 0x94, 0xe2, 0xb4, - 0x67, 0x27, 0xde, 0xf0, 0x80, 0xb1, 0x32, 0x35, - 0x6d, 0x45, 0x21, 0x12, 0x2c, 0x0d, 0xf4, 0x38, - 0x06, 0x9b, 0x58, 0x1a, 0x8f, 0x79, 0xe9, 0x70, - 0xd0, 0xc2, 0xad, 0xa8, 0x50, 0x75, 0x84, 0x48, - 0xca, 0xfc, 0xda, 0x8a, 0xd6, 0x54, 0x42, 0x24, - 0xbf, 0x98, 0x95, 0xf9, 0xe3, 0x5e, 0xb5, 0x15, - 0x68, 0x61, 0x28, 0xba, 0xdf, 0x4c, 0xf1, 0x2f, - 0x81, 0xe6, 0xb2, 0x3f, 0x33, 0xee, 0x36, 0x10, - 0x6e, 0x18, 0x46, 0xa6, 0x22, 0x88, 0x13, 0xf7, - 0x2d, 0xb8, 0x0e, 0x3d, 0xf5, 0xa4, 0x39, 0x3b, - 0x07, 0x9e, 0x9c, 0x9d, 0x59, 0x9f, 0x1b, 0x08, - 0x90, 0x09, 0x7a, 0x1c, 0xea, 0xa0, 0x71, 0x5a, - 0xd1, 0x1d, 0xc3, 0x7b, 0xae, 0x0a, 0xa9, 0x91, - 0x51, 0x5b, 0x76, 0x72, 0x85, 0xa1, 0x49, 0xeb, - 0xcb, 0x7c, 0xfd, 0xc4, 0xdb, 0x1e, 0x8b, 0xd2, - 0xd7, 0x92, 0x55, 0xaa, 0x43, 0x0b, 0x25, 0xaf, - 0xc0, 0x73, 0x99, 0x77, 0x96, 0x5c, 0xfa, 0x52, - 0xe4, 0xec, 0x5f, 0x4a, 0xb6, 0xa2, 0x16, 0x86, - 0x69, 0xc5, 0x62, 0xfe, 0x29, 0x7d, 0xbb, 0xcc, - 0xe0, 0xd3, 0x4d, 0x8c, 0xf2, 0x1f, 0x30, 0xdc, - 0x82, 0xab, 0xe7, 0x56, 0xb3, 0x93, 0x40, 0xd8, - 0x34, 0xb0, 0xef, 0x26, 0x37, 0x0c, 0x11, 0x44, - 0x6f, 0x78, 0x19, 0x9a, 0x47, 0x74, 0xa7, 0xc1, - 0x23, 0x53, 0x89, 0xfb, 0x14, 0x5d, 0xf8, 0x97, - 0x2e, 0x4b, 0xb9, 0x60, 0x0f, 0xed, 0x3e, 0xe5, - 0xf6, 0x87, 0xa5, 0x17, 0x3a, 0xa3, 0x3c, 0xb7 -}; - -/* This is a multiplication table for the factor 0xc0 (i.e., r^105 (mod f(r)). - * gfmul_c0[f] returns r^105 * f(r) (modulo f(r)). - */ -static const __u8 gfmul_c0[256] = -{ - 0x00, 0xc0, 0x07, 0xc7, 0x0e, 0xce, 0x09, 0xc9, - 0x1c, 0xdc, 0x1b, 0xdb, 0x12, 0xd2, 0x15, 0xd5, - 0x38, 0xf8, 0x3f, 0xff, 0x36, 0xf6, 0x31, 0xf1, - 0x24, 0xe4, 0x23, 0xe3, 0x2a, 0xea, 0x2d, 0xed, - 0x70, 0xb0, 0x77, 0xb7, 0x7e, 0xbe, 0x79, 0xb9, - 0x6c, 0xac, 0x6b, 0xab, 0x62, 0xa2, 0x65, 0xa5, - 0x48, 0x88, 0x4f, 0x8f, 0x46, 0x86, 0x41, 0x81, - 0x54, 0x94, 0x53, 0x93, 0x5a, 0x9a, 0x5d, 0x9d, - 0xe0, 0x20, 0xe7, 0x27, 0xee, 0x2e, 0xe9, 0x29, - 0xfc, 0x3c, 0xfb, 0x3b, 0xf2, 0x32, 0xf5, 0x35, - 0xd8, 0x18, 0xdf, 0x1f, 0xd6, 0x16, 0xd1, 0x11, - 0xc4, 0x04, 0xc3, 0x03, 0xca, 0x0a, 0xcd, 0x0d, - 0x90, 0x50, 0x97, 0x57, 0x9e, 0x5e, 0x99, 0x59, - 0x8c, 0x4c, 0x8b, 0x4b, 0x82, 0x42, 0x85, 0x45, - 0xa8, 0x68, 0xaf, 0x6f, 0xa6, 0x66, 0xa1, 0x61, - 0xb4, 0x74, 0xb3, 0x73, 0xba, 0x7a, 0xbd, 0x7d, - 0x47, 0x87, 0x40, 0x80, 0x49, 0x89, 0x4e, 0x8e, - 0x5b, 0x9b, 0x5c, 0x9c, 0x55, 0x95, 0x52, 0x92, - 0x7f, 0xbf, 0x78, 0xb8, 0x71, 0xb1, 0x76, 0xb6, - 0x63, 0xa3, 0x64, 0xa4, 0x6d, 0xad, 0x6a, 0xaa, - 0x37, 0xf7, 0x30, 0xf0, 0x39, 0xf9, 0x3e, 0xfe, - 0x2b, 0xeb, 0x2c, 0xec, 0x25, 0xe5, 0x22, 0xe2, - 0x0f, 0xcf, 0x08, 0xc8, 0x01, 0xc1, 0x06, 0xc6, - 0x13, 0xd3, 0x14, 0xd4, 0x1d, 0xdd, 0x1a, 0xda, - 0xa7, 0x67, 0xa0, 0x60, 0xa9, 0x69, 0xae, 0x6e, - 0xbb, 0x7b, 0xbc, 0x7c, 0xb5, 0x75, 0xb2, 0x72, - 0x9f, 0x5f, 0x98, 0x58, 0x91, 0x51, 0x96, 0x56, - 0x83, 0x43, 0x84, 0x44, 0x8d, 0x4d, 0x8a, 0x4a, - 0xd7, 0x17, 0xd0, 0x10, 0xd9, 0x19, 0xde, 0x1e, - 0xcb, 0x0b, 0xcc, 0x0c, 0xc5, 0x05, 0xc2, 0x02, - 0xef, 0x2f, 0xe8, 0x28, 0xe1, 0x21, 0xe6, 0x26, - 0xf3, 0x33, 0xf4, 0x34, 0xfd, 0x3d, 0xfa, 0x3a -}; - - -/* Returns V modulo 255 provided V is in the range -255,-254,...,509. - */ -static inline __u8 mod255(int v) -{ - if (v > 0) { - if (v < 255) { - return v; - } else { - return v - 255; - } - } else { - return v + 255; - } -} - - -/* Add two numbers in the field. Addition in this field is equivalent - * to a bit-wise exclusive OR operation---subtraction is therefore - * identical to addition. - */ -static inline __u8 gfadd(__u8 a, __u8 b) -{ - return a ^ b; -} - - -/* Add two vectors of numbers in the field. Each byte in A and B gets - * added individually. - */ -static inline unsigned long gfadd_long(unsigned long a, unsigned long b) -{ - return a ^ b; -} - - -/* Multiply two numbers in the field: - */ -static inline __u8 gfmul(__u8 a, __u8 b) -{ - if (a && b) { - return gfpow[mod255(gflog[a] + gflog[b])]; - } else { - return 0; - } -} - - -/* Just like gfmul, except we have already looked up the log of the - * second number. - */ -static inline __u8 gfmul_exp(__u8 a, int b) -{ - if (a) { - return gfpow[mod255(gflog[a] + b)]; - } else { - return 0; - } -} - - -/* Just like gfmul_exp, except that A is a vector of numbers. That - * is, each byte in A gets multiplied by gfpow[mod255(B)]. - */ -static inline unsigned long gfmul_exp_long(unsigned long a, int b) -{ - __u8 t; - - if (sizeof(long) == 4) { - return ( - ((t = (__u32)a >> 24 & 0xff) ? - (((__u32) gfpow[mod255(gflog[t] + b)]) << 24) : 0) | - ((t = (__u32)a >> 16 & 0xff) ? - (((__u32) gfpow[mod255(gflog[t] + b)]) << 16) : 0) | - ((t = (__u32)a >> 8 & 0xff) ? - (((__u32) gfpow[mod255(gflog[t] + b)]) << 8) : 0) | - ((t = (__u32)a >> 0 & 0xff) ? - (((__u32) gfpow[mod255(gflog[t] + b)]) << 0) : 0)); - } else if (sizeof(long) == 8) { - return ( - ((t = (__u64)a >> 56 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 56) : 0) | - ((t = (__u64)a >> 48 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 48) : 0) | - ((t = (__u64)a >> 40 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 40) : 0) | - ((t = (__u64)a >> 32 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 32) : 0) | - ((t = (__u64)a >> 24 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 24) : 0) | - ((t = (__u64)a >> 16 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 16) : 0) | - ((t = (__u64)a >> 8 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 8) : 0) | - ((t = (__u64)a >> 0 & 0xff) ? - (((__u64) gfpow[mod255(gflog[t] + b)]) << 0) : 0)); - } else { - TRACE_FUN(ft_t_any); - TRACE_ABORT(-1, ft_t_err, "Error: size of long is %d bytes", - (int)sizeof(long)); - } -} - - -/* Divide two numbers in the field. Returns a/b (modulo f(x)). - */ -static inline __u8 gfdiv(__u8 a, __u8 b) -{ - if (!b) { - TRACE_FUN(ft_t_any); - TRACE_ABORT(0xff, ft_t_bug, "Error: division by zero"); - } else if (a == 0) { - return 0; - } else { - return gfpow[mod255(gflog[a] - gflog[b])]; - } -} - - -/* The following functions return the inverse of the matrix of the - * linear system that needs to be solved to determine the error - * magnitudes. The first deals with matrices of rank 3, while the - * second deals with matrices of rank 2. The error indices are passed - * in arguments L0,..,L2 (0=first sector, 31=last sector). The error - * indices must be sorted in ascending order, i.e., L0<L1<L2. - * - * The linear system that needs to be solved for the error magnitudes - * is A * b = s, where s is the known vector of syndromes, b is the - * vector of error magnitudes and A in the ORDER=3 case: - * - * A_3 = {{1/r^L[0], 1/r^L[1], 1/r^L[2]}, - * { 1, 1, 1}, - * { r^L[0], r^L[1], r^L[2]}} - */ -static inline int gfinv3(__u8 l0, - __u8 l1, - __u8 l2, - Matrix Ainv) -{ - __u8 det; - __u8 t20, t10, t21, t12, t01, t02; - int log_det; - - /* compute some intermediate results: */ - t20 = gfpow[l2 - l0]; /* t20 = r^l2/r^l0 */ - t10 = gfpow[l1 - l0]; /* t10 = r^l1/r^l0 */ - t21 = gfpow[l2 - l1]; /* t21 = r^l2/r^l1 */ - t12 = gfpow[l1 - l2 + 255]; /* t12 = r^l1/r^l2 */ - t01 = gfpow[l0 - l1 + 255]; /* t01 = r^l0/r^l1 */ - t02 = gfpow[l0 - l2 + 255]; /* t02 = r^l0/r^l2 */ - /* Calculate the determinant of matrix A_3^-1 (sometimes - * called the Vandermonde determinant): - */ - det = gfadd(t20, gfadd(t10, gfadd(t21, gfadd(t12, gfadd(t01, t02))))); - if (!det) { - TRACE_FUN(ft_t_any); - TRACE_ABORT(0, ft_t_err, - "Inversion failed (3 CRC errors, >0 CRC failures)"); - } - log_det = 255 - gflog[det]; - - /* Now, calculate all of the coefficients: - */ - Ainv[0][0]= gfmul_exp(gfadd(gfpow[l1], gfpow[l2]), log_det); - Ainv[0][1]= gfmul_exp(gfadd(t21, t12), log_det); - Ainv[0][2]= gfmul_exp(gfadd(gfpow[255 - l1], gfpow[255 - l2]),log_det); - - Ainv[1][0]= gfmul_exp(gfadd(gfpow[l0], gfpow[l2]), log_det); - Ainv[1][1]= gfmul_exp(gfadd(t20, t02), log_det); - Ainv[1][2]= gfmul_exp(gfadd(gfpow[255 - l0], gfpow[255 - l2]),log_det); - - Ainv[2][0]= gfmul_exp(gfadd(gfpow[l0], gfpow[l1]), log_det); - Ainv[2][1]= gfmul_exp(gfadd(t10, t01), log_det); - Ainv[2][2]= gfmul_exp(gfadd(gfpow[255 - l0], gfpow[255 - l1]),log_det); - - return 1; -} - - -static inline int gfinv2(__u8 l0, __u8 l1, Matrix Ainv) -{ - __u8 det; - __u8 t1, t2; - int log_det; - - t1 = gfpow[255 - l0]; - t2 = gfpow[255 - l1]; - det = gfadd(t1, t2); - if (!det) { - TRACE_FUN(ft_t_any); - TRACE_ABORT(0, ft_t_err, - "Inversion failed (2 CRC errors, >0 CRC failures)"); - } - log_det = 255 - gflog[det]; - - /* Now, calculate all of the coefficients: - */ - Ainv[0][0] = Ainv[1][0] = gfpow[log_det]; - - Ainv[0][1] = gfmul_exp(t2, log_det); - Ainv[1][1] = gfmul_exp(t1, log_det); - - return 1; -} - - -/* Multiply matrix A by vector S and return result in vector B. M is - * assumed to be of order NxN, S and B of order Nx1. - */ -static inline void gfmat_mul(int n, Matrix A, - __u8 *s, __u8 *b) -{ - int i, j; - __u8 dot_prod; - - for (i = 0; i < n; ++i) { - dot_prod = 0; - for (j = 0; j < n; ++j) { - dot_prod = gfadd(dot_prod, gfmul(A[i][j], s[j])); - } - b[i] = dot_prod; - } -} - - - -/* The Reed Solomon ECC codes are computed over the N-th byte of each - * block, where N=SECTOR_SIZE. There are up to 29 blocks of data, and - * 3 blocks of ECC. The blocks are stored contiguously in memory. A - * segment, consequently, is assumed to have at least 4 blocks: one or - * more data blocks plus three ECC blocks. - * - * Notice: In QIC-80 speak, a CRC error is a sector with an incorrect - * CRC. A CRC failure is a sector with incorrect data, but - * a valid CRC. In the error control literature, the former - * is usually called "erasure", the latter "error." - */ -/* Compute the parity bytes for C columns of data, where C is the - * number of bytes that fit into a long integer. We use a linear - * feed-back register to do this. The parity bytes P[0], P[STRIDE], - * P[2*STRIDE] are computed such that: - * - * x^k * p(x) + m(x) = 0 (modulo g(x)) - * - * where k = NBLOCKS, - * p(x) = P[0] + P[STRIDE]*x + P[2*STRIDE]*x^2, and - * m(x) = sum_{i=0}^k m_i*x^i. - * m_i = DATA[i*SECTOR_SIZE] - */ -static inline void set_parity(unsigned long *data, - int nblocks, - unsigned long *p, - int stride) -{ - unsigned long p0, p1, p2, t1, t2, *end; - - end = data + nblocks * (FT_SECTOR_SIZE / sizeof(long)); - p0 = p1 = p2 = 0; - while (data < end) { - /* The new parity bytes p0_i, p1_i, p2_i are computed - * from the old values p0_{i-1}, p1_{i-1}, p2_{i-1} - * recursively as: - * - * p0_i = p1_{i-1} + r^105 * (m_{i-1} - p0_{i-1}) - * p1_i = p2_{i-1} + r^105 * (m_{i-1} - p0_{i-1}) - * p2_i = (m_{i-1} - p0_{i-1}) - * - * With the initial condition: p0_0 = p1_0 = p2_0 = 0. - */ - t1 = gfadd_long(*data, p0); - /* - * Multiply each byte in t1 by 0xc0: - */ - if (sizeof(long) == 4) { - t2= (((__u32) gfmul_c0[(__u32)t1 >> 24 & 0xff]) << 24 | - ((__u32) gfmul_c0[(__u32)t1 >> 16 & 0xff]) << 16 | - ((__u32) gfmul_c0[(__u32)t1 >> 8 & 0xff]) << 8 | - ((__u32) gfmul_c0[(__u32)t1 >> 0 & 0xff]) << 0); - } else if (sizeof(long) == 8) { - t2= (((__u64) gfmul_c0[(__u64)t1 >> 56 & 0xff]) << 56 | - ((__u64) gfmul_c0[(__u64)t1 >> 48 & 0xff]) << 48 | - ((__u64) gfmul_c0[(__u64)t1 >> 40 & 0xff]) << 40 | - ((__u64) gfmul_c0[(__u64)t1 >> 32 & 0xff]) << 32 | - ((__u64) gfmul_c0[(__u64)t1 >> 24 & 0xff]) << 24 | - ((__u64) gfmul_c0[(__u64)t1 >> 16 & 0xff]) << 16 | - ((__u64) gfmul_c0[(__u64)t1 >> 8 & 0xff]) << 8 | - ((__u64) gfmul_c0[(__u64)t1 >> 0 & 0xff]) << 0); - } else { - TRACE_FUN(ft_t_any); - TRACE(ft_t_err, "Error: long is of size %d", - (int) sizeof(long)); - TRACE_EXIT; - } - p0 = gfadd_long(t2, p1); - p1 = gfadd_long(t2, p2); - p2 = t1; - data += FT_SECTOR_SIZE / sizeof(long); - } - *p = p0; - p += stride; - *p = p1; - p += stride; - *p = p2; - return; -} - - -/* Compute the 3 syndrome values. DATA should point to the first byte - * of the column for which the syndromes are desired. The syndromes - * are computed over the first NBLOCKS of rows. The three bytes will - * be placed in S[0], S[1], and S[2]. - * - * S[i] is the value of the "message" polynomial m(x) evaluated at the - * i-th root of the generator polynomial g(x). - * - * As g(x)=(x-r^-1)(x-1)(x-r^1) we evaluate the message polynomial at - * x=r^-1 to get S[0], at x=r^0=1 to get S[1], and at x=r to get S[2]. - * This could be done directly and efficiently via the Horner scheme. - * However, it would require multiplication tables for the factors - * r^-1 (0xc3) and r (0x02). The following scheme does not require - * any multiplication tables beyond what's needed for set_parity() - * anyway and is slightly faster if there are no errors and slightly - * slower if there are errors. The latter is hopefully the infrequent - * case. - * - * To understand the alternative algorithm, notice that set_parity(m, - * k, p) computes parity bytes such that: - * - * x^k * p(x) = m(x) (modulo g(x)). - * - * That is, to evaluate m(r^m), where r^m is a root of g(x), we can - * simply evaluate (r^m)^k*p(r^m). Also, notice that p is 0 if and - * only if s is zero. That is, if all parity bytes are 0, we know - * there is no error in the data and consequently there is no need to - * compute s(x) at all! In all other cases, we compute s(x) from p(x) - * by evaluating (r^m)^k*p(r^m) for m=-1, m=0, and m=1. The p(x) - * polynomial is evaluated via the Horner scheme. - */ -static int compute_syndromes(unsigned long *data, int nblocks, unsigned long *s) -{ - unsigned long p[3]; - - set_parity(data, nblocks, p, 1); - if (p[0] | p[1] | p[2]) { - /* Some of the checked columns do not have a zero - * syndrome. For simplicity, we compute the syndromes - * for all columns that we have computed the - * remainders for. - */ - s[0] = gfmul_exp_long( - gfadd_long(p[0], - gfmul_exp_long( - gfadd_long(p[1], - gfmul_exp_long(p[2], -1)), - -1)), - -nblocks); - s[1] = gfadd_long(gfadd_long(p[2], p[1]), p[0]); - s[2] = gfmul_exp_long( - gfadd_long(p[0], - gfmul_exp_long( - gfadd_long(p[1], - gfmul_exp_long(p[2], 1)), - 1)), - nblocks); - return 0; - } else { - return 1; - } -} - - -/* Correct the block in the column pointed to by DATA. There are NBAD - * CRC errors and their indices are in BAD_LOC[0], up to - * BAD_LOC[NBAD-1]. If NBAD>1, Ainv holds the inverse of the matrix - * of the linear system that needs to be solved to determine the error - * magnitudes. S[0], S[1], and S[2] are the syndrome values. If row - * j gets corrected, then bit j will be set in CORRECTION_MAP. - */ -static inline int correct_block(__u8 *data, int nblocks, - int nbad, int *bad_loc, Matrix Ainv, - __u8 *s, - SectorMap * correction_map) -{ - int ncorrected = 0; - int i; - __u8 t1, t2; - __u8 c0, c1, c2; /* check bytes */ - __u8 error_mag[3], log_error_mag; - __u8 *dp, l, e; - TRACE_FUN(ft_t_any); - - switch (nbad) { - case 0: - /* might have a CRC failure: */ - if (s[0] == 0) { - /* more than one error */ - TRACE_ABORT(-1, ft_t_err, - "ECC failed (0 CRC errors, >1 CRC failures)"); - } - t1 = gfdiv(s[1], s[0]); - if ((bad_loc[nbad++] = gflog[t1]) >= nblocks) { - TRACE(ft_t_err, - "ECC failed (0 CRC errors, >1 CRC failures)"); - TRACE_ABORT(-1, ft_t_err, - "attempt to correct data at %d", bad_loc[0]); - } - error_mag[0] = s[1]; - break; - case 1: - t1 = gfadd(gfmul_exp(s[1], bad_loc[0]), s[2]); - t2 = gfadd(gfmul_exp(s[0], bad_loc[0]), s[1]); - if (t1 == 0 && t2 == 0) { - /* one erasure, no error: */ - Ainv[0][0] = gfpow[bad_loc[0]]; - } else if (t1 == 0 || t2 == 0) { - /* one erasure and more than one error: */ - TRACE_ABORT(-1, ft_t_err, - "ECC failed (1 erasure, >1 error)"); - } else { - /* one erasure, one error: */ - if ((bad_loc[nbad++] = gflog[gfdiv(t1, t2)]) - >= nblocks) { - TRACE(ft_t_err, "ECC failed " - "(1 CRC errors, >1 CRC failures)"); - TRACE_ABORT(-1, ft_t_err, - "attempt to correct data at %d", - bad_loc[1]); - } - if (!gfinv2(bad_loc[0], bad_loc[1], Ainv)) { - /* inversion failed---must have more - * than one error - */ - TRACE_EXIT -1; - } - } - /* FALL THROUGH TO ERROR MAGNITUDE COMPUTATION: - */ - case 2: - case 3: - /* compute error magnitudes: */ - gfmat_mul(nbad, Ainv, s, error_mag); - break; - - default: - TRACE_ABORT(-1, ft_t_err, - "Internal Error: number of CRC errors > 3"); - } - - /* Perform correction by adding ERROR_MAG[i] to the byte at - * offset BAD_LOC[i]. Also add the value of the computed - * error polynomial to the syndrome values. If the correction - * was successful, the resulting check bytes should be zero - * (i.e., the corrected data is a valid code word). - */ - c0 = s[0]; - c1 = s[1]; - c2 = s[2]; - for (i = 0; i < nbad; ++i) { - e = error_mag[i]; - if (e) { - /* correct the byte at offset L by magnitude E: */ - l = bad_loc[i]; - dp = &data[l * FT_SECTOR_SIZE]; - *dp = gfadd(*dp, e); - *correction_map |= 1 << l; - ++ncorrected; - - log_error_mag = gflog[e]; - c0 = gfadd(c0, gfpow[mod255(log_error_mag - l)]); - c1 = gfadd(c1, e); - c2 = gfadd(c2, gfpow[mod255(log_error_mag + l)]); - } - } - if (c0 || c1 || c2) { - TRACE_ABORT(-1, ft_t_err, - "ECC self-check failed, too many errors"); - } - TRACE_EXIT ncorrected; -} - - -#if defined(ECC_SANITY_CHECK) || defined(ECC_PARANOID) - -/* Perform a sanity check on the computed parity bytes: - */ -static int sanity_check(unsigned long *data, int nblocks) -{ - TRACE_FUN(ft_t_any); - unsigned long s[3]; - - if (!compute_syndromes(data, nblocks, s)) { - TRACE_ABORT(0, ft_bug, - "Internal Error: syndrome self-check failed"); - } - TRACE_EXIT 1; -} - -#endif /* defined(ECC_SANITY_CHECK) || defined(ECC_PARANOID) */ - -/* Compute the parity for an entire segment of data. - */ -int ftape_ecc_set_segment_parity(struct memory_segment *mseg) -{ - int i; - __u8 *parity_bytes; - - parity_bytes = &mseg->data[(mseg->blocks - 3) * FT_SECTOR_SIZE]; - for (i = 0; i < FT_SECTOR_SIZE; i += sizeof(long)) { - set_parity((unsigned long *) &mseg->data[i], mseg->blocks - 3, - (unsigned long *) &parity_bytes[i], - FT_SECTOR_SIZE / sizeof(long)); -#ifdef ECC_PARANOID - if (!sanity_check((unsigned long *) &mseg->data[i], - mseg->blocks)) { - return -1; - } -#endif /* ECC_PARANOID */ - } - return 0; -} - - -/* Checks and corrects (if possible) the segment MSEG. Returns one of - * ECC_OK, ECC_CORRECTED, and ECC_FAILED. - */ -int ftape_ecc_correct_data(struct memory_segment *mseg) -{ - int col, i, result; - int ncorrected = 0; - int nerasures = 0; /* # of erasures (CRC errors) */ - int erasure_loc[3]; /* erasure locations */ - unsigned long ss[3]; - __u8 s[3]; - Matrix Ainv; - TRACE_FUN(ft_t_flow); - - mseg->corrected = 0; - - /* find first column that has non-zero syndromes: */ - for (col = 0; col < FT_SECTOR_SIZE; col += sizeof(long)) { - if (!compute_syndromes((unsigned long *) &mseg->data[col], - mseg->blocks, ss)) { - /* something is wrong---have to fix things */ - break; - } - } - if (col >= FT_SECTOR_SIZE) { - /* all syndromes are ok, therefore nothing to correct */ - TRACE_EXIT ECC_OK; - } - /* count the number of CRC errors if there were any: */ - if (mseg->read_bad) { - for (i = 0; i < mseg->blocks; i++) { - if (BAD_CHECK(mseg->read_bad, i)) { - if (nerasures >= 3) { - /* this is too much for ECC */ - TRACE_ABORT(ECC_FAILED, ft_t_err, - "ECC failed (>3 CRC errors)"); - } /* if */ - erasure_loc[nerasures++] = i; - } - } - } - /* - * If there are at least 2 CRC errors, determine inverse of matrix - * of linear system to be solved: - */ - switch (nerasures) { - case 2: - if (!gfinv2(erasure_loc[0], erasure_loc[1], Ainv)) { - TRACE_EXIT ECC_FAILED; - } - break; - case 3: - if (!gfinv3(erasure_loc[0], erasure_loc[1], - erasure_loc[2], Ainv)) { - TRACE_EXIT ECC_FAILED; - } - break; - default: - /* this is not an error condition... */ - break; - } - - do { - for (i = 0; i < sizeof(long); ++i) { - s[0] = ss[0]; - s[1] = ss[1]; - s[2] = ss[2]; - if (s[0] | s[1] | s[2]) { -#ifdef BIG_ENDIAN - result = correct_block( - &mseg->data[col + sizeof(long) - 1 - i], - mseg->blocks, - nerasures, - erasure_loc, - Ainv, - s, - &mseg->corrected); -#else - result = correct_block(&mseg->data[col + i], - mseg->blocks, - nerasures, - erasure_loc, - Ainv, - s, - &mseg->corrected); -#endif - if (result < 0) { - TRACE_EXIT ECC_FAILED; - } - ncorrected += result; - } - ss[0] >>= 8; - ss[1] >>= 8; - ss[2] >>= 8; - } - -#ifdef ECC_SANITY_CHECK - if (!sanity_check((unsigned long *) &mseg->data[col], - mseg->blocks)) { - TRACE_EXIT ECC_FAILED; - } -#endif /* ECC_SANITY_CHECK */ - - /* find next column with non-zero syndromes: */ - while ((col += sizeof(long)) < FT_SECTOR_SIZE) { - if (!compute_syndromes((unsigned long *) - &mseg->data[col], mseg->blocks, ss)) { - /* something is wrong---have to fix things */ - break; - } - } - } while (col < FT_SECTOR_SIZE); - if (ncorrected && nerasures == 0) { - TRACE(ft_t_warn, "block contained error not caught by CRC"); - } - TRACE((ncorrected > 0) ? ft_t_noise : ft_t_any, "number of corrections: %d", ncorrected); - TRACE_EXIT ncorrected ? ECC_CORRECTED : ECC_OK; -} |
