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1da177e4 LT |
1 | /* |
2 | * ECC algorithm for M-systems disk on chip. We use the excellent Reed | |
3 | * Solmon code of Phil Karn (karn@ka9q.ampr.org) available under the | |
4 | * GNU GPL License. The rest is simply to convert the disk on chip | |
5 | * syndrom into a standard syndom. | |
6 | * | |
e5580fbe | 7 | * Author: Fabrice Bellard (fabrice.bellard@netgem.com) |
1da177e4 LT |
8 | * Copyright (C) 2000 Netgem S.A. |
9 | * | |
1da177e4 LT |
10 | * This program is free software; you can redistribute it and/or modify |
11 | * it under the terms of the GNU General Public License as published by | |
12 | * the Free Software Foundation; either version 2 of the License, or | |
13 | * (at your option) any later version. | |
14 | * | |
15 | * This program is distributed in the hope that it will be useful, | |
16 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
18 | * GNU General Public License for more details. | |
19 | * | |
20 | * You should have received a copy of the GNU General Public License | |
21 | * along with this program; if not, write to the Free Software | |
22 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
23 | */ | |
24 | #include <linux/kernel.h> | |
25 | #include <linux/module.h> | |
26 | #include <asm/errno.h> | |
27 | #include <asm/io.h> | |
28 | #include <asm/uaccess.h> | |
1da177e4 LT |
29 | #include <linux/delay.h> |
30 | #include <linux/slab.h> | |
1da177e4 LT |
31 | #include <linux/init.h> |
32 | #include <linux/types.h> | |
33 | ||
1da177e4 LT |
34 | #include <linux/mtd/mtd.h> |
35 | #include <linux/mtd/doc2000.h> | |
36 | ||
66c81f00 | 37 | #define DEBUG_ECC 0 |
1da177e4 LT |
38 | /* need to undef it (from asm/termbits.h) */ |
39 | #undef B0 | |
40 | ||
41 | #define MM 10 /* Symbol size in bits */ | |
42 | #define KK (1023-4) /* Number of data symbols per block */ | |
43 | #define B0 510 /* First root of generator polynomial, alpha form */ | |
44 | #define PRIM 1 /* power of alpha used to generate roots of generator poly */ | |
45 | #define NN ((1 << MM) - 1) | |
46 | ||
47 | typedef unsigned short dtype; | |
48 | ||
49 | /* 1+x^3+x^10 */ | |
50 | static const int Pp[MM+1] = { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1 }; | |
51 | ||
52 | /* This defines the type used to store an element of the Galois Field | |
53 | * used by the code. Make sure this is something larger than a char if | |
54 | * if anything larger than GF(256) is used. | |
55 | * | |
56 | * Note: unsigned char will work up to GF(256) but int seems to run | |
57 | * faster on the Pentium. | |
58 | */ | |
59 | typedef int gf; | |
60 | ||
61 | /* No legal value in index form represents zero, so | |
62 | * we need a special value for this purpose | |
63 | */ | |
64 | #define A0 (NN) | |
65 | ||
66 | /* Compute x % NN, where NN is 2**MM - 1, | |
67 | * without a slow divide | |
68 | */ | |
69 | static inline gf | |
70 | modnn(int x) | |
71 | { | |
72 | while (x >= NN) { | |
73 | x -= NN; | |
74 | x = (x >> MM) + (x & NN); | |
75 | } | |
76 | return x; | |
77 | } | |
78 | ||
79 | #define CLEAR(a,n) {\ | |
80 | int ci;\ | |
81 | for(ci=(n)-1;ci >=0;ci--)\ | |
82 | (a)[ci] = 0;\ | |
83 | } | |
84 | ||
85 | #define COPY(a,b,n) {\ | |
86 | int ci;\ | |
87 | for(ci=(n)-1;ci >=0;ci--)\ | |
88 | (a)[ci] = (b)[ci];\ | |
89 | } | |
90 | ||
91 | #define COPYDOWN(a,b,n) {\ | |
92 | int ci;\ | |
93 | for(ci=(n)-1;ci >=0;ci--)\ | |
94 | (a)[ci] = (b)[ci];\ | |
95 | } | |
96 | ||
97 | #define Ldec 1 | |
98 | ||
99 | /* generate GF(2**m) from the irreducible polynomial p(X) in Pp[0]..Pp[m] | |
100 | lookup tables: index->polynomial form alpha_to[] contains j=alpha**i; | |
101 | polynomial form -> index form index_of[j=alpha**i] = i | |
102 | alpha=2 is the primitive element of GF(2**m) | |
103 | HARI's COMMENT: (4/13/94) alpha_to[] can be used as follows: | |
104 | Let @ represent the primitive element commonly called "alpha" that | |
105 | is the root of the primitive polynomial p(x). Then in GF(2^m), for any | |
106 | 0 <= i <= 2^m-2, | |
107 | @^i = a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1) | |
108 | where the binary vector (a(0),a(1),a(2),...,a(m-1)) is the representation | |
109 | of the integer "alpha_to[i]" with a(0) being the LSB and a(m-1) the MSB. Thus for | |
110 | example the polynomial representation of @^5 would be given by the binary | |
111 | representation of the integer "alpha_to[5]". | |
25985edc | 112 | Similarly, index_of[] can be used as follows: |
1da177e4 LT |
113 | As above, let @ represent the primitive element of GF(2^m) that is |
114 | the root of the primitive polynomial p(x). In order to find the power | |
115 | of @ (alpha) that has the polynomial representation | |
116 | a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1) | |
117 | we consider the integer "i" whose binary representation with a(0) being LSB | |
118 | and a(m-1) MSB is (a(0),a(1),...,a(m-1)) and locate the entry | |
e5580fbe | 119 | "index_of[i]". Now, @^index_of[i] is that element whose polynomial |
1da177e4 LT |
120 | representation is (a(0),a(1),a(2),...,a(m-1)). |
121 | NOTE: | |
122 | The element alpha_to[2^m-1] = 0 always signifying that the | |
123 | representation of "@^infinity" = 0 is (0,0,0,...,0). | |
25985edc | 124 | Similarly, the element index_of[0] = A0 always signifying |
1da177e4 LT |
125 | that the power of alpha which has the polynomial representation |
126 | (0,0,...,0) is "infinity". | |
e5580fbe | 127 | |
1da177e4 LT |
128 | */ |
129 | ||
130 | static void | |
131 | generate_gf(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1]) | |
132 | { | |
133 | register int i, mask; | |
134 | ||
135 | mask = 1; | |
136 | Alpha_to[MM] = 0; | |
137 | for (i = 0; i < MM; i++) { | |
138 | Alpha_to[i] = mask; | |
139 | Index_of[Alpha_to[i]] = i; | |
140 | /* If Pp[i] == 1 then, term @^i occurs in poly-repr of @^MM */ | |
141 | if (Pp[i] != 0) | |
142 | Alpha_to[MM] ^= mask; /* Bit-wise EXOR operation */ | |
143 | mask <<= 1; /* single left-shift */ | |
144 | } | |
145 | Index_of[Alpha_to[MM]] = MM; | |
146 | /* | |
147 | * Have obtained poly-repr of @^MM. Poly-repr of @^(i+1) is given by | |
148 | * poly-repr of @^i shifted left one-bit and accounting for any @^MM | |
149 | * term that may occur when poly-repr of @^i is shifted. | |
150 | */ | |
151 | mask >>= 1; | |
152 | for (i = MM + 1; i < NN; i++) { | |
153 | if (Alpha_to[i - 1] >= mask) | |
154 | Alpha_to[i] = Alpha_to[MM] ^ ((Alpha_to[i - 1] ^ mask) << 1); | |
155 | else | |
156 | Alpha_to[i] = Alpha_to[i - 1] << 1; | |
157 | Index_of[Alpha_to[i]] = i; | |
158 | } | |
159 | Index_of[0] = A0; | |
160 | Alpha_to[NN] = 0; | |
161 | } | |
162 | ||
163 | /* | |
164 | * Performs ERRORS+ERASURES decoding of RS codes. bb[] is the content | |
165 | * of the feedback shift register after having processed the data and | |
166 | * the ECC. | |
167 | * | |
168 | * Return number of symbols corrected, or -1 if codeword is illegal | |
169 | * or uncorrectable. If eras_pos is non-null, the detected error locations | |
170 | * are written back. NOTE! This array must be at least NN-KK elements long. | |
171 | * The corrected data are written in eras_val[]. They must be xor with the data | |
172 | * to retrieve the correct data : data[erase_pos[i]] ^= erase_val[i] . | |
e5580fbe | 173 | * |
1da177e4 LT |
174 | * First "no_eras" erasures are declared by the calling program. Then, the |
175 | * maximum # of errors correctable is t_after_eras = floor((NN-KK-no_eras)/2). | |
176 | * If the number of channel errors is not greater than "t_after_eras" the | |
177 | * transmitted codeword will be recovered. Details of algorithm can be found | |
178 | * in R. Blahut's "Theory ... of Error-Correcting Codes". | |
179 | ||
180 | * Warning: the eras_pos[] array must not contain duplicate entries; decoder failure | |
181 | * will result. The decoder *could* check for this condition, but it would involve | |
182 | * extra time on every decoding operation. | |
183 | * */ | |
184 | static int | |
185 | eras_dec_rs(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1], | |
e5580fbe | 186 | gf bb[NN - KK + 1], gf eras_val[NN-KK], int eras_pos[NN-KK], |
1da177e4 LT |
187 | int no_eras) |
188 | { | |
189 | int deg_lambda, el, deg_omega; | |
190 | int i, j, r,k; | |
191 | gf u,q,tmp,num1,num2,den,discr_r; | |
192 | gf lambda[NN-KK + 1], s[NN-KK + 1]; /* Err+Eras Locator poly | |
193 | * and syndrome poly */ | |
194 | gf b[NN-KK + 1], t[NN-KK + 1], omega[NN-KK + 1]; | |
195 | gf root[NN-KK], reg[NN-KK + 1], loc[NN-KK]; | |
196 | int syn_error, count; | |
197 | ||
198 | syn_error = 0; | |
199 | for(i=0;i<NN-KK;i++) | |
200 | syn_error |= bb[i]; | |
201 | ||
202 | if (!syn_error) { | |
203 | /* if remainder is zero, data[] is a codeword and there are no | |
204 | * errors to correct. So return data[] unmodified | |
205 | */ | |
206 | count = 0; | |
207 | goto finish; | |
208 | } | |
e5580fbe | 209 | |
1da177e4 LT |
210 | for(i=1;i<=NN-KK;i++){ |
211 | s[i] = bb[0]; | |
212 | } | |
213 | for(j=1;j<NN-KK;j++){ | |
214 | if(bb[j] == 0) | |
215 | continue; | |
216 | tmp = Index_of[bb[j]]; | |
e5580fbe | 217 | |
1da177e4 LT |
218 | for(i=1;i<=NN-KK;i++) |
219 | s[i] ^= Alpha_to[modnn(tmp + (B0+i-1)*PRIM*j)]; | |
220 | } | |
221 | ||
222 | /* undo the feedback register implicit multiplication and convert | |
223 | syndromes to index form */ | |
224 | ||
225 | for(i=1;i<=NN-KK;i++) { | |
226 | tmp = Index_of[s[i]]; | |
227 | if (tmp != A0) | |
228 | tmp = modnn(tmp + 2 * KK * (B0+i-1)*PRIM); | |
229 | s[i] = tmp; | |
230 | } | |
e5580fbe | 231 | |
1da177e4 LT |
232 | CLEAR(&lambda[1],NN-KK); |
233 | lambda[0] = 1; | |
234 | ||
235 | if (no_eras > 0) { | |
236 | /* Init lambda to be the erasure locator polynomial */ | |
237 | lambda[1] = Alpha_to[modnn(PRIM * eras_pos[0])]; | |
238 | for (i = 1; i < no_eras; i++) { | |
239 | u = modnn(PRIM*eras_pos[i]); | |
240 | for (j = i+1; j > 0; j--) { | |
241 | tmp = Index_of[lambda[j - 1]]; | |
242 | if(tmp != A0) | |
243 | lambda[j] ^= Alpha_to[modnn(u + tmp)]; | |
244 | } | |
245 | } | |
66c81f00 | 246 | #if DEBUG_ECC >= 1 |
1da177e4 LT |
247 | /* Test code that verifies the erasure locator polynomial just constructed |
248 | Needed only for decoder debugging. */ | |
e5580fbe | 249 | |
1da177e4 LT |
250 | /* find roots of the erasure location polynomial */ |
251 | for(i=1;i<=no_eras;i++) | |
252 | reg[i] = Index_of[lambda[i]]; | |
253 | count = 0; | |
254 | for (i = 1,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) { | |
255 | q = 1; | |
256 | for (j = 1; j <= no_eras; j++) | |
257 | if (reg[j] != A0) { | |
258 | reg[j] = modnn(reg[j] + j); | |
259 | q ^= Alpha_to[reg[j]]; | |
260 | } | |
261 | if (q != 0) | |
262 | continue; | |
263 | /* store root and error location number indices */ | |
264 | root[count] = i; | |
265 | loc[count] = k; | |
266 | count++; | |
267 | } | |
268 | if (count != no_eras) { | |
269 | printf("\n lambda(x) is WRONG\n"); | |
270 | count = -1; | |
271 | goto finish; | |
272 | } | |
66c81f00 | 273 | #if DEBUG_ECC >= 2 |
1da177e4 LT |
274 | printf("\n Erasure positions as determined by roots of Eras Loc Poly:\n"); |
275 | for (i = 0; i < count; i++) | |
276 | printf("%d ", loc[i]); | |
277 | printf("\n"); | |
278 | #endif | |
279 | #endif | |
280 | } | |
281 | for(i=0;i<NN-KK+1;i++) | |
282 | b[i] = Index_of[lambda[i]]; | |
e5580fbe | 283 | |
1da177e4 LT |
284 | /* |
285 | * Begin Berlekamp-Massey algorithm to determine error+erasure | |
286 | * locator polynomial | |
287 | */ | |
288 | r = no_eras; | |
289 | el = no_eras; | |
290 | while (++r <= NN-KK) { /* r is the step number */ | |
291 | /* Compute discrepancy at the r-th step in poly-form */ | |
292 | discr_r = 0; | |
293 | for (i = 0; i < r; i++){ | |
294 | if ((lambda[i] != 0) && (s[r - i] != A0)) { | |
295 | discr_r ^= Alpha_to[modnn(Index_of[lambda[i]] + s[r - i])]; | |
296 | } | |
297 | } | |
298 | discr_r = Index_of[discr_r]; /* Index form */ | |
299 | if (discr_r == A0) { | |
300 | /* 2 lines below: B(x) <-- x*B(x) */ | |
301 | COPYDOWN(&b[1],b,NN-KK); | |
302 | b[0] = A0; | |
303 | } else { | |
304 | /* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */ | |
305 | t[0] = lambda[0]; | |
306 | for (i = 0 ; i < NN-KK; i++) { | |
307 | if(b[i] != A0) | |
308 | t[i+1] = lambda[i+1] ^ Alpha_to[modnn(discr_r + b[i])]; | |
309 | else | |
310 | t[i+1] = lambda[i+1]; | |
311 | } | |
312 | if (2 * el <= r + no_eras - 1) { | |
313 | el = r + no_eras - el; | |
314 | /* | |
315 | * 2 lines below: B(x) <-- inv(discr_r) * | |
316 | * lambda(x) | |
317 | */ | |
318 | for (i = 0; i <= NN-KK; i++) | |
319 | b[i] = (lambda[i] == 0) ? A0 : modnn(Index_of[lambda[i]] - discr_r + NN); | |
320 | } else { | |
321 | /* 2 lines below: B(x) <-- x*B(x) */ | |
322 | COPYDOWN(&b[1],b,NN-KK); | |
323 | b[0] = A0; | |
324 | } | |
325 | COPY(lambda,t,NN-KK+1); | |
326 | } | |
327 | } | |
328 | ||
329 | /* Convert lambda to index form and compute deg(lambda(x)) */ | |
330 | deg_lambda = 0; | |
331 | for(i=0;i<NN-KK+1;i++){ | |
332 | lambda[i] = Index_of[lambda[i]]; | |
333 | if(lambda[i] != A0) | |
334 | deg_lambda = i; | |
335 | } | |
336 | /* | |
337 | * Find roots of the error+erasure locator polynomial by Chien | |
338 | * Search | |
339 | */ | |
340 | COPY(®[1],&lambda[1],NN-KK); | |
341 | count = 0; /* Number of roots of lambda(x) */ | |
342 | for (i = 1,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) { | |
343 | q = 1; | |
344 | for (j = deg_lambda; j > 0; j--){ | |
345 | if (reg[j] != A0) { | |
346 | reg[j] = modnn(reg[j] + j); | |
347 | q ^= Alpha_to[reg[j]]; | |
348 | } | |
349 | } | |
350 | if (q != 0) | |
351 | continue; | |
352 | /* store root (index-form) and error location number */ | |
353 | root[count] = i; | |
354 | loc[count] = k; | |
355 | /* If we've already found max possible roots, | |
356 | * abort the search to save time | |
357 | */ | |
358 | if(++count == deg_lambda) | |
359 | break; | |
360 | } | |
361 | if (deg_lambda != count) { | |
362 | /* | |
363 | * deg(lambda) unequal to number of roots => uncorrectable | |
364 | * error detected | |
365 | */ | |
366 | count = -1; | |
367 | goto finish; | |
368 | } | |
369 | /* | |
370 | * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo | |
371 | * x**(NN-KK)). in index form. Also find deg(omega). | |
372 | */ | |
373 | deg_omega = 0; | |
374 | for (i = 0; i < NN-KK;i++){ | |
375 | tmp = 0; | |
376 | j = (deg_lambda < i) ? deg_lambda : i; | |
377 | for(;j >= 0; j--){ | |
378 | if ((s[i + 1 - j] != A0) && (lambda[j] != A0)) | |
379 | tmp ^= Alpha_to[modnn(s[i + 1 - j] + lambda[j])]; | |
380 | } | |
381 | if(tmp != 0) | |
382 | deg_omega = i; | |
383 | omega[i] = Index_of[tmp]; | |
384 | } | |
385 | omega[NN-KK] = A0; | |
e5580fbe | 386 | |
1da177e4 LT |
387 | /* |
388 | * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 = | |
389 | * inv(X(l))**(B0-1) and den = lambda_pr(inv(X(l))) all in poly-form | |
390 | */ | |
391 | for (j = count-1; j >=0; j--) { | |
392 | num1 = 0; | |
393 | for (i = deg_omega; i >= 0; i--) { | |
394 | if (omega[i] != A0) | |
395 | num1 ^= Alpha_to[modnn(omega[i] + i * root[j])]; | |
396 | } | |
397 | num2 = Alpha_to[modnn(root[j] * (B0 - 1) + NN)]; | |
398 | den = 0; | |
e5580fbe | 399 | |
1da177e4 LT |
400 | /* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */ |
401 | for (i = min(deg_lambda,NN-KK-1) & ~1; i >= 0; i -=2) { | |
402 | if(lambda[i+1] != A0) | |
403 | den ^= Alpha_to[modnn(lambda[i+1] + i * root[j])]; | |
404 | } | |
405 | if (den == 0) { | |
66c81f00 | 406 | #if DEBUG_ECC >= 1 |
1da177e4 LT |
407 | printf("\n ERROR: denominator = 0\n"); |
408 | #endif | |
409 | /* Convert to dual- basis */ | |
410 | count = -1; | |
411 | goto finish; | |
412 | } | |
413 | /* Apply error to data */ | |
414 | if (num1 != 0) { | |
415 | eras_val[j] = Alpha_to[modnn(Index_of[num1] + Index_of[num2] + NN - Index_of[den])]; | |
416 | } else { | |
417 | eras_val[j] = 0; | |
418 | } | |
419 | } | |
420 | finish: | |
421 | for(i=0;i<count;i++) | |
422 | eras_pos[i] = loc[i]; | |
423 | return count; | |
424 | } | |
425 | ||
426 | /***************************************************************************/ | |
427 | /* The DOC specific code begins here */ | |
428 | ||
429 | #define SECTOR_SIZE 512 | |
430 | /* The sector bytes are packed into NB_DATA MM bits words */ | |
431 | #define NB_DATA (((SECTOR_SIZE + 1) * 8 + 6) / MM) | |
432 | ||
e5580fbe | 433 | /* |
1da177e4 LT |
434 | * Correct the errors in 'sector[]' by using 'ecc1[]' which is the |
435 | * content of the feedback shift register applyied to the sector and | |
436 | * the ECC. Return the number of errors corrected (and correct them in | |
e5580fbe | 437 | * sector), or -1 if error |
1da177e4 LT |
438 | */ |
439 | int doc_decode_ecc(unsigned char sector[SECTOR_SIZE], unsigned char ecc1[6]) | |
440 | { | |
441 | int parity, i, nb_errors; | |
442 | gf bb[NN - KK + 1]; | |
443 | gf error_val[NN-KK]; | |
444 | int error_pos[NN-KK], pos, bitpos, index, val; | |
445 | dtype *Alpha_to, *Index_of; | |
446 | ||
447 | /* init log and exp tables here to save memory. However, it is slower */ | |
448 | Alpha_to = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL); | |
449 | if (!Alpha_to) | |
450 | return -1; | |
e5580fbe | 451 | |
1da177e4 LT |
452 | Index_of = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL); |
453 | if (!Index_of) { | |
454 | kfree(Alpha_to); | |
455 | return -1; | |
456 | } | |
457 | ||
458 | generate_gf(Alpha_to, Index_of); | |
459 | ||
460 | parity = ecc1[1]; | |
461 | ||
462 | bb[0] = (ecc1[4] & 0xff) | ((ecc1[5] & 0x03) << 8); | |
463 | bb[1] = ((ecc1[5] & 0xfc) >> 2) | ((ecc1[2] & 0x0f) << 6); | |
464 | bb[2] = ((ecc1[2] & 0xf0) >> 4) | ((ecc1[3] & 0x3f) << 4); | |
465 | bb[3] = ((ecc1[3] & 0xc0) >> 6) | ((ecc1[0] & 0xff) << 2); | |
466 | ||
e5580fbe | 467 | nb_errors = eras_dec_rs(Alpha_to, Index_of, bb, |
1da177e4 LT |
468 | error_val, error_pos, 0); |
469 | if (nb_errors <= 0) | |
470 | goto the_end; | |
471 | ||
472 | /* correct the errors */ | |
473 | for(i=0;i<nb_errors;i++) { | |
474 | pos = error_pos[i]; | |
475 | if (pos >= NB_DATA && pos < KK) { | |
476 | nb_errors = -1; | |
477 | goto the_end; | |
478 | } | |
479 | if (pos < NB_DATA) { | |
480 | /* extract bit position (MSB first) */ | |
481 | pos = 10 * (NB_DATA - 1 - pos) - 6; | |
482 | /* now correct the following 10 bits. At most two bytes | |
483 | can be modified since pos is even */ | |
484 | index = (pos >> 3) ^ 1; | |
485 | bitpos = pos & 7; | |
e5580fbe | 486 | if ((index >= 0 && index < SECTOR_SIZE) || |
1da177e4 LT |
487 | index == (SECTOR_SIZE + 1)) { |
488 | val = error_val[i] >> (2 + bitpos); | |
489 | parity ^= val; | |
490 | if (index < SECTOR_SIZE) | |
491 | sector[index] ^= val; | |
492 | } | |
493 | index = ((pos >> 3) + 1) ^ 1; | |
494 | bitpos = (bitpos + 10) & 7; | |
495 | if (bitpos == 0) | |
496 | bitpos = 8; | |
e5580fbe | 497 | if ((index >= 0 && index < SECTOR_SIZE) || |
1da177e4 LT |
498 | index == (SECTOR_SIZE + 1)) { |
499 | val = error_val[i] << (8 - bitpos); | |
500 | parity ^= val; | |
501 | if (index < SECTOR_SIZE) | |
502 | sector[index] ^= val; | |
503 | } | |
504 | } | |
505 | } | |
e5580fbe | 506 | |
1da177e4 LT |
507 | /* use parity to test extra errors */ |
508 | if ((parity & 0xff) != 0) | |
509 | nb_errors = -1; | |
510 | ||
511 | the_end: | |
512 | kfree(Alpha_to); | |
513 | kfree(Index_of); | |
514 | return nb_errors; | |
515 | } | |
516 | ||
517 | EXPORT_SYMBOL_GPL(doc_decode_ecc); | |
518 | ||
519 | MODULE_LICENSE("GPL"); | |
520 | MODULE_AUTHOR("Fabrice Bellard <fabrice.bellard@netgem.com>"); | |
521 | MODULE_DESCRIPTION("ECC code for correcting errors detected by DiskOnChip 2000 and Millennium ECC hardware"); |