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1/*
2 * Generic binary BCH encoding/decoding library
3 *
4 * This program is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 as published by
6 * the Free Software Foundation.
7 *
8 * This program is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
11 * more details.
12 *
13 * You should have received a copy of the GNU General Public License along with
14 * this program; if not, write to the Free Software Foundation, Inc., 51
15 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
16 *
17 * Copyright © 2011 Parrot S.A.
18 *
19 * Author: Ivan Djelic <ivan.djelic@parrot.com>
20 *
21 * Description:
22 *
23 * This library provides runtime configurable encoding/decoding of binary
24 * Bose-Chaudhuri-Hocquenghem (BCH) codes.
25 *
26 * Call init_bch to get a pointer to a newly allocated bch_control structure for
27 * the given m (Galois field order), t (error correction capability) and
28 * (optional) primitive polynomial parameters.
29 *
30 * Call encode_bch to compute and store ecc parity bytes to a given buffer.
31 * Call decode_bch to detect and locate errors in received data.
32 *
33 * On systems supporting hw BCH features, intermediate results may be provided
34 * to decode_bch in order to skip certain steps. See decode_bch() documentation
35 * for details.
36 *
37 * Option CONFIG_BCH_CONST_PARAMS can be used to force fixed values of
38 * parameters m and t; thus allowing extra compiler optimizations and providing
39 * better (up to 2x) encoding performance. Using this option makes sense when
40 * (m,t) are fixed and known in advance, e.g. when using BCH error correction
41 * on a particular NAND flash device.
42 *
43 * Algorithmic details:
44 *
45 * Encoding is performed by processing 32 input bits in parallel, using 4
46 * remainder lookup tables.
47 *
48 * The final stage of decoding involves the following internal steps:
49 * a. Syndrome computation
50 * b. Error locator polynomial computation using Berlekamp-Massey algorithm
51 * c. Error locator root finding (by far the most expensive step)
52 *
53 * In this implementation, step c is not performed using the usual Chien search.
54 * Instead, an alternative approach described in [1] is used. It consists in
55 * factoring the error locator polynomial using the Berlekamp Trace algorithm
56 * (BTA) down to a certain degree (4), after which ad hoc low-degree polynomial
57 * solving techniques [2] are used. The resulting algorithm, called BTZ, yields
58 * much better performance than Chien search for usual (m,t) values (typically
59 * m >= 13, t < 32, see [1]).
60 *
61 * [1] B. Biswas, V. Herbert. Efficient root finding of polynomials over fields
62 * of characteristic 2, in: Western European Workshop on Research in Cryptology
63 * - WEWoRC 2009, Graz, Austria, LNCS, Springer, July 2009, to appear.
64 * [2] [Zin96] V.A. Zinoviev. On the solution of equations of degree 10 over
65 * finite fields GF(2^q). In Rapport de recherche INRIA no 2829, 1996.
66 */
67
68#include <stdlib.h>
69#include <string.h>
70#include <errno.h>
71#include "libbch.h"
72
73/* glue code */
74#define kmalloc(x,y) malloc(x)
75#define kfree(x) free(x)
76
77static void *kzalloc(size_t size, int flags)
78{
79 (void)flags;
80 void *p = malloc(size);
81
82 if (p)
83 memset(p, 0, size);
84
85 return p;
86}
87
88#define EXPORT_SYMBOL_GPL(x)
89#define MODULE_LICENSE(x)
90#define MODULE_AUTHOR(x)
91#define MODULE_DESCRIPTION(x)
92
93#define DIV_ROUND_UP(n,d) (((n) + (d) - 1)/(d))
94
95#include <arpa/inet.h>
96#define cpu_to_be32(x) htonl(x)
97
98static inline int fls(int x)
99{
100 int r = 32;
101 if (!x)
102 return 0;
103
104 if (!(x & 0xffff0000u)) {
105 x <<= 16;
106 r -= 16;
107 }
108
109 if (!(x & 0xff000000u)) {
110 x <<= 8;
111 r -= 8;
112 }
113
114 if (!(x & 0xf0000000u)) {
115 x <<= 4;
116 r -= 4;
117 }
118
119 if (!(x & 0xc0000000u)) {
120 x <<= 2;
121 r -= 2;
122 }
123
124 if (!(x & 0x80000000u)) {
125 x <<= 1;
126 r -= 1;
127 }
128
129 return r;
130}
131
132#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
133#define GFP_KERNEL 0
134/* end of glue code */
135
136/*
137 * same as encode_bch(), but process input data one byte at a time
138 */
139static void encode_bch_unaligned(struct bch_control *bch,
140 const unsigned char *data, unsigned int len,
141 uint32_t *ecc)
142{
143 int i;
144 const uint32_t *p;
145 const int l = BCH_ECC_WORDS(bch)-1;
146
147 while (len--) {
148 p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(*data++)) & 0xff);
149
150 for (i = 0; i < l; i++)
151 ecc[i] = ((ecc[i] << 8)|(ecc[i+1] >> 24))^(*p++);
152
153 ecc[l] = (ecc[l] << 8)^(*p);
154 }
155}
156
157/*
158 * convert ecc bytes to aligned, zero-padded 32-bit ecc words
159 */
160static void load_ecc8(struct bch_control *bch, uint32_t *dst,
161 const uint8_t *src)
162{
163 uint8_t pad[4] = {0, 0, 0, 0};
164 unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
165
166 for (i = 0; i < nwords; i++, src += 4)
167 dst[i] = (src[0] << 24)|(src[1] << 16)|(src[2] << 8)|src[3];
168
169 memcpy(pad, src, BCH_ECC_BYTES(bch)-4*nwords);
170 dst[nwords] = (pad[0] << 24)|(pad[1] << 16)|(pad[2] << 8)|pad[3];
171}
172
173/*
174 * convert 32-bit ecc words to ecc bytes
175 */
176static void store_ecc8(struct bch_control *bch, uint8_t *dst,
177 const uint32_t *src)
178{
179 uint8_t pad[4];
180 unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
181
182 for (i = 0; i < nwords; i++) {
183 *dst++ = (src[i] >> 24);
184 *dst++ = (src[i] >> 16) & 0xff;
185 *dst++ = (src[i] >> 8) & 0xff;
186 *dst++ = (src[i] >> 0) & 0xff;
187 }
188 pad[0] = (src[nwords] >> 24);
189 pad[1] = (src[nwords] >> 16) & 0xff;
190 pad[2] = (src[nwords] >> 8) & 0xff;
191 pad[3] = (src[nwords] >> 0) & 0xff;
192 memcpy(dst, pad, BCH_ECC_BYTES(bch)-4*nwords);
193}
194
195/**
196 * encode_bch - calculate BCH ecc parity of data
197 * @bch: BCH control structure
198 * @data: data to encode
199 * @len: data length in bytes
200 * @ecc: ecc parity data, must be initialized by caller
201 *
202 * The @ecc parity array is used both as input and output parameter, in order to
203 * allow incremental computations. It should be of the size indicated by member
204 * @ecc_bytes of @bch, and should be initialized to 0 before the first call.
205 *
206 * The exact number of computed ecc parity bits is given by member @ecc_bits of
207 * @bch; it may be less than m*t for large values of t.
208 */
209void encode_bch(struct bch_control *bch, const uint8_t *data,
210 unsigned int len, uint8_t *ecc)
211{
212 const unsigned int l = BCH_ECC_WORDS(bch)-1;
213 unsigned int i, mlen;
214 unsigned long m;
215 uint32_t w, r[l+1];
216 const uint32_t * const tab0 = bch->mod8_tab;
217 const uint32_t * const tab1 = tab0 + 256*(l+1);
218 const uint32_t * const tab2 = tab1 + 256*(l+1);
219 const uint32_t * const tab3 = tab2 + 256*(l+1);
220 const uint32_t *pdata, *p0, *p1, *p2, *p3;
221
222 if (ecc) {
223 /* load ecc parity bytes into internal 32-bit buffer */
224 load_ecc8(bch, bch->ecc_buf, ecc);
225 } else {
226 memset(bch->ecc_buf, 0, sizeof(r));
227 }
228
229 /* process first unaligned data bytes */
230 m = ((unsigned long)data) & 3;
231 if (m) {
232 mlen = (len < (4-m)) ? len : 4-m;
233 encode_bch_unaligned(bch, data, mlen, bch->ecc_buf);
234 data += mlen;
235 len -= mlen;
236 }
237
238 /* process 32-bit aligned data words */
239 pdata = (uint32_t *)data;
240 mlen = len/4;
241 data += 4*mlen;
242 len -= 4*mlen;
243 memcpy(r, bch->ecc_buf, sizeof(r));
244
245 /*
246 * split each 32-bit word into 4 polynomials of weight 8 as follows:
247 *
248 * 31 ...24 23 ...16 15 ... 8 7 ... 0
249 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt
250 * tttttttt mod g = r0 (precomputed)
251 * zzzzzzzz 00000000 mod g = r1 (precomputed)
252 * yyyyyyyy 00000000 00000000 mod g = r2 (precomputed)
253 * xxxxxxxx 00000000 00000000 00000000 mod g = r3 (precomputed)
254 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt mod g = r0^r1^r2^r3
255 */
256 while (mlen--) {
257 /* input data is read in big-endian format */
258 w = r[0]^cpu_to_be32(*pdata++);
259 p0 = tab0 + (l+1)*((w >> 0) & 0xff);
260 p1 = tab1 + (l+1)*((w >> 8) & 0xff);
261 p2 = tab2 + (l+1)*((w >> 16) & 0xff);
262 p3 = tab3 + (l+1)*((w >> 24) & 0xff);
263
264 for (i = 0; i < l; i++)
265 r[i] = r[i+1]^p0[i]^p1[i]^p2[i]^p3[i];
266
267 r[l] = p0[l]^p1[l]^p2[l]^p3[l];
268 }
269 memcpy(bch->ecc_buf, r, sizeof(r));
270
271 /* process last unaligned bytes */
272 if (len)
273 encode_bch_unaligned(bch, data, len, bch->ecc_buf);
274
275 /* store ecc parity bytes into original parity buffer */
276 if (ecc)
277 store_ecc8(bch, ecc, bch->ecc_buf);
278}
279EXPORT_SYMBOL_GPL(encode_bch);
280
281static inline int modulo(struct bch_control *bch, unsigned int v)
282{
283 const unsigned int n = GF_N(bch);
284 while (v >= n) {
285 v -= n;
286 v = (v & n) + (v >> GF_M(bch));
287 }
288 return v;
289}
290
291/*
292 * shorter and faster modulo function, only works when v < 2N.
293 */
294static inline int mod_s(struct bch_control *bch, unsigned int v)
295{
296 const unsigned int n = GF_N(bch);
297 return (v < n) ? v : v-n;
298}
299
300static inline int deg(unsigned int poly)
301{
302 /* polynomial degree is the most-significant bit index */
303 return fls(poly)-1;
304}
305
306static inline int parity(unsigned int x)
307{
308 /*
309 * public domain code snippet, lifted from
310 * http://www-graphics.stanford.edu/~seander/bithacks.html
311 */
312 x ^= x >> 1;
313 x ^= x >> 2;
314 x = (x & 0x11111111U) * 0x11111111U;
315 return (x >> 28) & 1;
316}
317
318/* Galois field basic operations: multiply, divide, inverse, etc. */
319
320static inline unsigned int gf_mul(struct bch_control *bch, unsigned int a,
321 unsigned int b)
322{
323 return (a && b) ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
324 bch->a_log_tab[b])] : 0;
325}
326
327static inline unsigned int gf_sqr(struct bch_control *bch, unsigned int a)
328{
329 return a ? bch->a_pow_tab[mod_s(bch, 2*bch->a_log_tab[a])] : 0;
330}
331
332static inline unsigned int gf_div(struct bch_control *bch, unsigned int a,
333 unsigned int b)
334{
335 return a ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
336 GF_N(bch)-bch->a_log_tab[b])] : 0;
337}
338
339static inline unsigned int gf_inv(struct bch_control *bch, unsigned int a)
340{
341 return bch->a_pow_tab[GF_N(bch)-bch->a_log_tab[a]];
342}
343
344static inline unsigned int a_pow(struct bch_control *bch, int i)
345{
346 return bch->a_pow_tab[modulo(bch, i)];
347}
348
349static inline int a_log(struct bch_control *bch, unsigned int x)
350{
351 return bch->a_log_tab[x];
352}
353
354static inline int a_ilog(struct bch_control *bch, unsigned int x)
355{
356 return mod_s(bch, GF_N(bch)-bch->a_log_tab[x]);
357}
358
359/*
360 * compute 2t syndromes of ecc polynomial, i.e. ecc(a^j) for j=1..2t
361 */
362static void compute_syndromes(struct bch_control *bch, uint32_t *ecc,
363 unsigned int *syn)
364{
365 int i, j, s;
366 unsigned int m;
367 uint32_t poly;
368 const int t = GF_T(bch);
369
370 s = bch->ecc_bits;
371
372 /* make sure extra bits in last ecc word are cleared */
373 m = ((unsigned int)s) & 31;
374 if (m)
375 ecc[s/32] &= ~((1u << (32-m))-1);
376 memset(syn, 0, 2*t*sizeof(*syn));
377
378 /* compute v(a^j) for j=1 .. 2t-1 */
379 do {
380 poly = *ecc++;
381 s -= 32;
382 while (poly) {
383 i = deg(poly);
384 for (j = 0; j < 2*t; j += 2)
385 syn[j] ^= a_pow(bch, (j+1)*(i+s));
386
387 poly ^= (1 << i);
388 }
389 } while (s > 0);
390
391 /* v(a^(2j)) = v(a^j)^2 */
392 for (j = 0; j < t; j++)
393 syn[2*j+1] = gf_sqr(bch, syn[j]);
394}
395
396static void gf_poly_copy(struct gf_poly *dst, struct gf_poly *src)
397{
398 memcpy(dst, src, GF_POLY_SZ(src->deg));
399}
400
401static int compute_error_locator_polynomial(struct bch_control *bch,
402 const unsigned int *syn)
403{
404 const unsigned int t = GF_T(bch);
405 const unsigned int n = GF_N(bch);
406 unsigned int i, j, tmp, l, pd = 1, d = syn[0];
407 struct gf_poly *elp = bch->elp;
408 struct gf_poly *pelp = bch->poly_2t[0];
409 struct gf_poly *elp_copy = bch->poly_2t[1];
410 int k, pp = -1;
411
412 memset(pelp, 0, GF_POLY_SZ(2*t));
413 memset(elp, 0, GF_POLY_SZ(2*t));
414
415 pelp->deg = 0;
416 pelp->c[0] = 1;
417 elp->deg = 0;
418 elp->c[0] = 1;
419
420 /* use simplified binary Berlekamp-Massey algorithm */
421 for (i = 0; (i < t) && (elp->deg <= t); i++) {
422 if (d) {
423 k = 2*i-pp;
424 gf_poly_copy(elp_copy, elp);
425 /* e[i+1](X) = e[i](X)+di*dp^-1*X^2(i-p)*e[p](X) */
426 tmp = a_log(bch, d)+n-a_log(bch, pd);
427 for (j = 0; j <= pelp->deg; j++) {
428 if (pelp->c[j]) {
429 l = a_log(bch, pelp->c[j]);
430 elp->c[j+k] ^= a_pow(bch, tmp+l);
431 }
432 }
433 /* compute l[i+1] = max(l[i]->c[l[p]+2*(i-p]) */
434 tmp = pelp->deg+k;
435 if (tmp > elp->deg) {
436 elp->deg = tmp;
437 gf_poly_copy(pelp, elp_copy);
438 pd = d;
439 pp = 2*i;
440 }
441 }
442 /* di+1 = S(2i+3)+elp[i+1].1*S(2i+2)+...+elp[i+1].lS(2i+3-l) */
443 if (i < t-1) {
444 d = syn[2*i+2];
445 for (j = 1; j <= elp->deg; j++)
446 d ^= gf_mul(bch, elp->c[j], syn[2*i+2-j]);
447 }
448 }
449 dbg("elp=%s\n", gf_poly_str(elp));
450 return (elp->deg > t) ? -1 : (int)elp->deg;
451}
452
453/*
454 * solve a m x m linear system in GF(2) with an expected number of solutions,
455 * and return the number of found solutions
456 */
457static int solve_linear_system(struct bch_control *bch, unsigned int *rows,
458 unsigned int *sol, int nsol)
459{
460 const int m = GF_M(bch);
461 unsigned int tmp, mask;
462 int rem, c, r, p, k, param[m];
463
464 k = 0;
465 mask = 1 << m;
466
467 /* Gaussian elimination */
468 for (c = 0; c < m; c++) {
469 rem = 0;
470 p = c-k;
471 /* find suitable row for elimination */
472 for (r = p; r < m; r++) {
473 if (rows[r] & mask) {
474 if (r != p) {
475 tmp = rows[r];
476 rows[r] = rows[p];
477 rows[p] = tmp;
478 }
479 rem = r+1;
480 break;
481 }
482 }
483 if (rem) {
484 /* perform elimination on remaining rows */
485 tmp = rows[p];
486 for (r = rem; r < m; r++) {
487 if (rows[r] & mask)
488 rows[r] ^= tmp;
489 }
490 } else {
491 /* elimination not needed, store defective row index */
492 param[k++] = c;
493 }
494 mask >>= 1;
495 }
496 /* rewrite system, inserting fake parameter rows */
497 if (k > 0) {
498 p = k;
499 for (r = m-1; r >= 0; r--) {
500 if ((r > m-1-k) && rows[r])
501 /* system has no solution */
502 return 0;
503
504 rows[r] = (p && (r == param[p-1])) ?
505 p--, 1u << (m-r) : rows[r-p];
506 }
507 }
508
509 if (nsol != (1 << k))
510 /* unexpected number of solutions */
511 return 0;
512
513 for (p = 0; p < nsol; p++) {
514 /* set parameters for p-th solution */
515 for (c = 0; c < k; c++)
516 rows[param[c]] = (rows[param[c]] & ~1)|((p >> c) & 1);
517
518 /* compute unique solution */
519 tmp = 0;
520 for (r = m-1; r >= 0; r--) {
521 mask = rows[r] & (tmp|1);
522 tmp |= parity(mask) << (m-r);
523 }
524 sol[p] = tmp >> 1;
525 }
526 return nsol;
527}
528
529/*
530 * this function builds and solves a linear system for finding roots of a degree
531 * 4 affine monic polynomial X^4+aX^2+bX+c over GF(2^m).
532 */
533static int find_affine4_roots(struct bch_control *bch, unsigned int a,
534 unsigned int b, unsigned int c,
535 unsigned int *roots)
536{
537 int i, j, k;
538 const int m = GF_M(bch);
539 unsigned int mask = 0xff, t, rows[16] = {0,};
540
541 j = a_log(bch, b);
542 k = a_log(bch, a);
543 rows[0] = c;
544
545 /* buid linear system to solve X^4+aX^2+bX+c = 0 */
546 for (i = 0; i < m; i++) {
547 rows[i+1] = bch->a_pow_tab[4*i]^
548 (a ? bch->a_pow_tab[mod_s(bch, k)] : 0)^
549 (b ? bch->a_pow_tab[mod_s(bch, j)] : 0);
550 j++;
551 k += 2;
552 }
553 /*
554 * transpose 16x16 matrix before passing it to linear solver
555 * warning: this code assumes m < 16
556 */
557 for (j = 8; j != 0; j >>= 1, mask ^= (mask << j)) {
558 for (k = 0; k < 16; k = (k+j+1) & ~j) {
559 t = ((rows[k] >> j)^rows[k+j]) & mask;
560 rows[k] ^= (t << j);
561 rows[k+j] ^= t;
562 }
563 }
564 return solve_linear_system(bch, rows, roots, 4);
565}
566
567/*
568 * compute root r of a degree 1 polynomial over GF(2^m) (returned as log(1/r))
569 */
570static int find_poly_deg1_roots(struct bch_control *bch, struct gf_poly *poly,
571 unsigned int *roots)
572{
573 int n = 0;
574
575 if (poly->c[0])
576 /* poly[X] = bX+c with c!=0, root=c/b */
577 roots[n++] = mod_s(bch, GF_N(bch)-bch->a_log_tab[poly->c[0]]+
578 bch->a_log_tab[poly->c[1]]);
579 return n;
580}
581
582/*
583 * compute roots of a degree 2 polynomial over GF(2^m)
584 */
585static int find_poly_deg2_roots(struct bch_control *bch, struct gf_poly *poly,
586 unsigned int *roots)
587{
588 int n = 0, i, l0, l1, l2;
589 unsigned int u, v, r;
590
591 if (poly->c[0] && poly->c[1]) {
592
593 l0 = bch->a_log_tab[poly->c[0]];
594 l1 = bch->a_log_tab[poly->c[1]];
595 l2 = bch->a_log_tab[poly->c[2]];
596
597 /* using z=a/bX, transform aX^2+bX+c into z^2+z+u (u=ac/b^2) */
598 u = a_pow(bch, l0+l2+2*(GF_N(bch)-l1));
599 /*
600 * let u = sum(li.a^i) i=0..m-1; then compute r = sum(li.xi):
601 * r^2+r = sum(li.(xi^2+xi)) = sum(li.(a^i+Tr(a^i).a^k)) =
602 * u + sum(li.Tr(a^i).a^k) = u+a^k.Tr(sum(li.a^i)) = u+a^k.Tr(u)
603 * i.e. r and r+1 are roots iff Tr(u)=0
604 */
605 r = 0;
606 v = u;
607 while (v) {
608 i = deg(v);
609 r ^= bch->xi_tab[i];
610 v ^= (1 << i);
611 }
612 /* verify root */
613 if ((gf_sqr(bch, r)^r) == u) {
614 /* reverse z=a/bX transformation and compute log(1/r) */
615 roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
616 bch->a_log_tab[r]+l2);
617 roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
618 bch->a_log_tab[r^1]+l2);
619 }
620 }
621 return n;
622}
623
624/*
625 * compute roots of a degree 3 polynomial over GF(2^m)
626 */
627static int find_poly_deg3_roots(struct bch_control *bch, struct gf_poly *poly,
628 unsigned int *roots)
629{
630 int i, n = 0;
631 unsigned int a, b, c, a2, b2, c2, e3, tmp[4];
632
633 if (poly->c[0]) {
634 /* transform polynomial into monic X^3 + a2X^2 + b2X + c2 */
635 e3 = poly->c[3];
636 c2 = gf_div(bch, poly->c[0], e3);
637 b2 = gf_div(bch, poly->c[1], e3);
638 a2 = gf_div(bch, poly->c[2], e3);
639
640 /* (X+a2)(X^3+a2X^2+b2X+c2) = X^4+aX^2+bX+c (affine) */
641 c = gf_mul(bch, a2, c2); /* c = a2c2 */
642 b = gf_mul(bch, a2, b2)^c2; /* b = a2b2 + c2 */
643 a = gf_sqr(bch, a2)^b2; /* a = a2^2 + b2 */
644
645 /* find the 4 roots of this affine polynomial */
646 if (find_affine4_roots(bch, a, b, c, tmp) == 4) {
647 /* remove a2 from final list of roots */
648 for (i = 0; i < 4; i++) {
649 if (tmp[i] != a2)
650 roots[n++] = a_ilog(bch, tmp[i]);
651 }
652 }
653 }
654 return n;
655}
656
657/*
658 * compute roots of a degree 4 polynomial over GF(2^m)
659 */
660static int find_poly_deg4_roots(struct bch_control *bch, struct gf_poly *poly,
661 unsigned int *roots)
662{
663 int i, l, n = 0;
664 unsigned int a, b, c, d, e = 0, f, a2, b2, c2, e4;
665
666 if (poly->c[0] == 0)
667 return 0;
668
669 /* transform polynomial into monic X^4 + aX^3 + bX^2 + cX + d */
670 e4 = poly->c[4];
671 d = gf_div(bch, poly->c[0], e4);
672 c = gf_div(bch, poly->c[1], e4);
673 b = gf_div(bch, poly->c[2], e4);
674 a = gf_div(bch, poly->c[3], e4);
675
676 /* use Y=1/X transformation to get an affine polynomial */
677 if (a) {
678 /* first, eliminate cX by using z=X+e with ae^2+c=0 */
679 if (c) {
680 /* compute e such that e^2 = c/a */
681 f = gf_div(bch, c, a);
682 l = a_log(bch, f);
683 l += (l & 1) ? GF_N(bch) : 0;
684 e = a_pow(bch, l/2);
685 /*
686 * use transformation z=X+e:
687 * z^4+e^4 + a(z^3+ez^2+e^2z+e^3) + b(z^2+e^2) +cz+ce+d
688 * z^4 + az^3 + (ae+b)z^2 + (ae^2+c)z+e^4+be^2+ae^3+ce+d
689 * z^4 + az^3 + (ae+b)z^2 + e^4+be^2+d
690 * z^4 + az^3 + b'z^2 + d'
691 */
692 d = a_pow(bch, 2*l)^gf_mul(bch, b, f)^d;
693 b = gf_mul(bch, a, e)^b;
694 }
695 /* now, use Y=1/X to get Y^4 + b/dY^2 + a/dY + 1/d */
696 if (d == 0)
697 /* assume all roots have multiplicity 1 */
698 return 0;
699
700 c2 = gf_inv(bch, d);
701 b2 = gf_div(bch, a, d);
702 a2 = gf_div(bch, b, d);
703 } else {
704 /* polynomial is already affine */
705 c2 = d;
706 b2 = c;
707 a2 = b;
708 }
709 /* find the 4 roots of this affine polynomial */
710 if (find_affine4_roots(bch, a2, b2, c2, roots) == 4) {
711 for (i = 0; i < 4; i++) {
712 /* post-process roots (reverse transformations) */
713 f = a ? gf_inv(bch, roots[i]) : roots[i];
714 roots[i] = a_ilog(bch, f^e);
715 }
716 n = 4;
717 }
718 return n;
719}
720
721/*
722 * build monic, log-based representation of a polynomial
723 */
724static void gf_poly_logrep(struct bch_control *bch,
725 const struct gf_poly *a, int *rep)
726{
727 int i, d = a->deg, l = GF_N(bch)-a_log(bch, a->c[a->deg]);
728
729 /* represent 0 values with -1; warning, rep[d] is not set to 1 */
730 for (i = 0; i < d; i++)
731 rep[i] = a->c[i] ? mod_s(bch, a_log(bch, a->c[i])+l) : -1;
732}
733
734/*
735 * compute polynomial Euclidean division remainder in GF(2^m)[X]
736 */
737static void gf_poly_mod(struct bch_control *bch, struct gf_poly *a,
738 const struct gf_poly *b, int *rep)
739{
740 int la, p, m;
741 unsigned int i, j, *c = a->c;
742 const unsigned int d = b->deg;
743
744 if (a->deg < d)
745 return;
746
747 /* reuse or compute log representation of denominator */
748 if (!rep) {
749 rep = bch->cache;
750 gf_poly_logrep(bch, b, rep);
751 }
752
753 for (j = a->deg; j >= d; j--) {
754 if (c[j]) {
755 la = a_log(bch, c[j]);
756 p = j-d;
757 for (i = 0; i < d; i++, p++) {
758 m = rep[i];
759 if (m >= 0)
760 c[p] ^= bch->a_pow_tab[mod_s(bch,
761 m+la)];
762 }
763 }
764 }
765 a->deg = d-1;
766 while (!c[a->deg] && a->deg)
767 a->deg--;
768}
769
770/*
771 * compute polynomial Euclidean division quotient in GF(2^m)[X]
772 */
773static void gf_poly_div(struct bch_control *bch, struct gf_poly *a,
774 const struct gf_poly *b, struct gf_poly *q)
775{
776 if (a->deg >= b->deg) {
777 q->deg = a->deg-b->deg;
778 /* compute a mod b (modifies a) */
779 gf_poly_mod(bch, a, b, NULL);
780 /* quotient is stored in upper part of polynomial a */
781 memcpy(q->c, &a->c[b->deg], (1+q->deg)*sizeof(unsigned int));
782 } else {
783 q->deg = 0;
784 q->c[0] = 0;
785 }
786}
787
788/*
789 * compute polynomial GCD (Greatest Common Divisor) in GF(2^m)[X]
790 */
791static struct gf_poly *gf_poly_gcd(struct bch_control *bch, struct gf_poly *a,
792 struct gf_poly *b)
793{
794 struct gf_poly *tmp;
795
796 dbg("gcd(%s,%s)=", gf_poly_str(a), gf_poly_str(b));
797
798 if (a->deg < b->deg) {
799 tmp = b;
800 b = a;
801 a = tmp;
802 }
803
804 while (b->deg > 0) {
805 gf_poly_mod(bch, a, b, NULL);
806 tmp = b;
807 b = a;
808 a = tmp;
809 }
810
811 dbg("%s\n", gf_poly_str(a));
812
813 return a;
814}
815
816/*
817 * Given a polynomial f and an integer k, compute Tr(a^kX) mod f
818 * This is used in Berlekamp Trace algorithm for splitting polynomials
819 */
820static void compute_trace_bk_mod(struct bch_control *bch, int k,
821 const struct gf_poly *f, struct gf_poly *z,
822 struct gf_poly *out)
823{
824 const int m = GF_M(bch);
825 int i, j;
826
827 /* z contains z^2j mod f */
828 z->deg = 1;
829 z->c[0] = 0;
830 z->c[1] = bch->a_pow_tab[k];
831
832 out->deg = 0;
833 memset(out, 0, GF_POLY_SZ(f->deg));
834
835 /* compute f log representation only once */
836 gf_poly_logrep(bch, f, bch->cache);
837
838 for (i = 0; i < m; i++) {
839 /* add a^(k*2^i)(z^(2^i) mod f) and compute (z^(2^i) mod f)^2 */
840 for (j = z->deg; j >= 0; j--) {
841 out->c[j] ^= z->c[j];
842 z->c[2*j] = gf_sqr(bch, z->c[j]);
843 z->c[2*j+1] = 0;
844 }
845 if (z->deg > out->deg)
846 out->deg = z->deg;
847
848 if (i < m-1) {
849 z->deg *= 2;
850 /* z^(2(i+1)) mod f = (z^(2^i) mod f)^2 mod f */
851 gf_poly_mod(bch, z, f, bch->cache);
852 }
853 }
854 while (!out->c[out->deg] && out->deg)
855 out->deg--;
856
857 dbg("Tr(a^%d.X) mod f = %s\n", k, gf_poly_str(out));
858}
859
860/*
861 * factor a polynomial using Berlekamp Trace algorithm (BTA)
862 */
863static void factor_polynomial(struct bch_control *bch, int k, struct gf_poly *f,
864 struct gf_poly **g, struct gf_poly **h)
865{
866 struct gf_poly *f2 = bch->poly_2t[0];
867 struct gf_poly *q = bch->poly_2t[1];
868 struct gf_poly *tk = bch->poly_2t[2];
869 struct gf_poly *z = bch->poly_2t[3];
870 struct gf_poly *gcd;
871
872 dbg("factoring %s...\n", gf_poly_str(f));
873
874 *g = f;
875 *h = NULL;
876
877 /* tk = Tr(a^k.X) mod f */
878 compute_trace_bk_mod(bch, k, f, z, tk);
879
880 if (tk->deg > 0) {
881 /* compute g = gcd(f, tk) (destructive operation) */
882 gf_poly_copy(f2, f);
883 gcd = gf_poly_gcd(bch, f2, tk);
884 if (gcd->deg < f->deg) {
885 /* compute h=f/gcd(f,tk); this will modify f and q */
886 gf_poly_div(bch, f, gcd, q);
887 /* store g and h in-place (clobbering f) */
888 *h = &((struct gf_poly_deg1 *)f)[gcd->deg].poly;
889 gf_poly_copy(*g, gcd);
890 gf_poly_copy(*h, q);
891 }
892 }
893}
894
895/*
896 * find roots of a polynomial, using BTZ algorithm; see the beginning of this
897 * file for details
898 */
899static int find_poly_roots(struct bch_control *bch, unsigned int k,
900 struct gf_poly *poly, unsigned int *roots)
901{
902 int cnt;
903 struct gf_poly *f1, *f2;
904
905 switch (poly->deg) {
906 /* handle low degree polynomials with ad hoc techniques */
907 case 1:
908 cnt = find_poly_deg1_roots(bch, poly, roots);
909 break;
910 case 2:
911 cnt = find_poly_deg2_roots(bch, poly, roots);
912 break;
913 case 3:
914 cnt = find_poly_deg3_roots(bch, poly, roots);
915 break;
916 case 4:
917 cnt = find_poly_deg4_roots(bch, poly, roots);
918 break;
919 default:
920 /* factor polynomial using Berlekamp Trace Algorithm (BTA) */
921 cnt = 0;
922 if (poly->deg && (k <= GF_M(bch))) {
923 factor_polynomial(bch, k, poly, &f1, &f2);
924 if (f1)
925 cnt += find_poly_roots(bch, k+1, f1, roots);
926 if (f2)
927 cnt += find_poly_roots(bch, k+1, f2, roots+cnt);
928 }
929 break;
930 }
931 return cnt;
932}
933
934#if defined(USE_CHIEN_SEARCH)
935/*
936 * exhaustive root search (Chien) implementation - not used, included only for
937 * reference/comparison tests
938 */
939static int chien_search(struct bch_control *bch, unsigned int len,
940 struct gf_poly *p, unsigned int *roots)
941{
942 int m;
943 unsigned int i, j, syn, syn0, count = 0;
944 const unsigned int k = 8*len+bch->ecc_bits;
945
946 /* use a log-based representation of polynomial */
947 gf_poly_logrep(bch, p, bch->cache);
948 bch->cache[p->deg] = 0;
949 syn0 = gf_div(bch, p->c[0], p->c[p->deg]);
950
951 for (i = GF_N(bch)-k+1; i <= GF_N(bch); i++) {
952 /* compute elp(a^i) */
953 for (j = 1, syn = syn0; j <= p->deg; j++) {
954 m = bch->cache[j];
955 if (m >= 0)
956 syn ^= a_pow(bch, m+j*i);
957 }
958 if (syn == 0) {
959 roots[count++] = GF_N(bch)-i;
960 if (count == p->deg)
961 break;
962 }
963 }
964 return (count == p->deg) ? count : 0;
965}
966#define find_poly_roots(_p, _k, _elp, _loc) chien_search(_p, len, _elp, _loc)
967#endif /* USE_CHIEN_SEARCH */
968
969/**
970 * decode_bch - decode received codeword and find bit error locations
971 * @bch: BCH control structure
972 * @data: received data, ignored if @calc_ecc is provided
973 * @len: data length in bytes, must always be provided
974 * @recv_ecc: received ecc, if NULL then assume it was XORed in @calc_ecc
975 * @calc_ecc: calculated ecc, if NULL then calc_ecc is computed from @data
976 * @syn: hw computed syndrome data (if NULL, syndrome is calculated)
977 * @errloc: output array of error locations
978 *
979 * Returns:
980 * The number of errors found, or -EBADMSG if decoding failed, or -EINVAL if
981 * invalid parameters were provided
982 *
983 * Depending on the available hw BCH support and the need to compute @calc_ecc
984 * separately (using encode_bch()), this function should be called with one of
985 * the following parameter configurations -
986 *
987 * by providing @data and @recv_ecc only:
988 * decode_bch(@bch, @data, @len, @recv_ecc, NULL, NULL, @errloc)
989 *
990 * by providing @recv_ecc and @calc_ecc:
991 * decode_bch(@bch, NULL, @len, @recv_ecc, @calc_ecc, NULL, @errloc)
992 *
993 * by providing ecc = recv_ecc XOR calc_ecc:
994 * decode_bch(@bch, NULL, @len, NULL, ecc, NULL, @errloc)
995 *
996 * by providing syndrome results @syn:
997 * decode_bch(@bch, NULL, @len, NULL, NULL, @syn, @errloc)
998 *
999 * Once decode_bch() has successfully returned with a positive value, error
1000 * locations returned in array @errloc should be interpreted as follows -
1001 *
1002 * if (errloc[n] >= 8*len), then n-th error is located in ecc (no need for
1003 * data correction)
1004 *
1005 * if (errloc[n] < 8*len), then n-th error is located in data and can be
1006 * corrected with statement data[errloc[n]/8] ^= 1 << (errloc[n] % 8);
1007 *
1008 * Note that this function does not perform any data correction by itself, it
1009 * merely indicates error locations.
1010 */
1011int decode_bch(struct bch_control *bch, const uint8_t *data, unsigned int len,
1012 const uint8_t *recv_ecc, const uint8_t *calc_ecc,
1013 const unsigned int *syn, unsigned int *errloc)
1014{
1015 const unsigned int ecc_words = BCH_ECC_WORDS(bch);
1016 unsigned int nbits;
1017 int i, err, nroots;
1018 uint32_t sum;
1019
1020 /* sanity check: make sure data length can be handled */
1021 if (8*len > (bch->n-bch->ecc_bits))
1022 return -EINVAL;
1023
1024 /* if caller does not provide syndromes, compute them */
1025 if (!syn) {
1026 if (!calc_ecc) {
1027 /* compute received data ecc into an internal buffer */
1028 if (!data || !recv_ecc)
1029 return -EINVAL;
1030 encode_bch(bch, data, len, NULL);
1031 } else {
1032 /* load provided calculated ecc */
1033 load_ecc8(bch, bch->ecc_buf, calc_ecc);
1034 }
1035 /* load received ecc or assume it was XORed in calc_ecc */
1036 if (recv_ecc) {
1037 load_ecc8(bch, bch->ecc_buf2, recv_ecc);
1038 /* XOR received and calculated ecc */
1039 for (i = 0, sum = 0; i < (int)ecc_words; i++) {
1040 bch->ecc_buf[i] ^= bch->ecc_buf2[i];
1041 sum |= bch->ecc_buf[i];
1042 }
1043 if (!sum)
1044 /* no error found */
1045 return 0;
1046 }
1047 compute_syndromes(bch, bch->ecc_buf, bch->syn);
1048 syn = bch->syn;
1049 }
1050
1051 err = compute_error_locator_polynomial(bch, syn);
1052 if (err > 0) {
1053 nroots = find_poly_roots(bch, 1, bch->elp, errloc);
1054 if (err != nroots)
1055 err = -1;
1056 }
1057 if (err > 0) {
1058 /* post-process raw error locations for easier correction */
1059 nbits = (len*8)+bch->ecc_bits;
1060 for (i = 0; i < err; i++) {
1061 if (errloc[i] >= nbits) {
1062 err = -2;
1063 break;
1064 }
1065 errloc[i] = nbits-1-errloc[i];
1066 errloc[i] = (errloc[i] & ~7)|(7-(errloc[i] & 7));
1067 }
1068 }
1069 return err;
1070}
1071EXPORT_SYMBOL_GPL(decode_bch);
1072
1073/*
1074 * generate Galois field lookup tables
1075 */
1076static int build_gf_tables(struct bch_control *bch, unsigned int poly)
1077{
1078 unsigned int i, x = 1;
1079 const unsigned int k = 1 << deg(poly);
1080
1081 /* primitive polynomial must be of degree m */
1082 if (k != (1u << GF_M(bch)))
1083 return -1;
1084
1085 for (i = 0; i < GF_N(bch); i++) {
1086 bch->a_pow_tab[i] = x;
1087 bch->a_log_tab[x] = i;
1088 if (i && (x == 1))
1089 /* polynomial is not primitive (a^i=1 with 0<i<2^m-1) */
1090 return -1;
1091 x <<= 1;
1092 if (x & k)
1093 x ^= poly;
1094 }
1095 bch->a_pow_tab[GF_N(bch)] = 1;
1096 bch->a_log_tab[0] = 0;
1097
1098 return 0;
1099}
1100
1101/*
1102 * compute generator polynomial remainder tables for fast encoding
1103 */
1104static void build_mod8_tables(struct bch_control *bch, const uint32_t *g)
1105{
1106 int i, j, b, d;
1107 uint32_t data, hi, lo, *tab;
1108 const int l = BCH_ECC_WORDS(bch);
1109 const int plen = DIV_ROUND_UP(bch->ecc_bits+1, 32);
1110 const int ecclen = DIV_ROUND_UP(bch->ecc_bits, 32);
1111
1112 memset(bch->mod8_tab, 0, 4*256*l*sizeof(*bch->mod8_tab));
1113
1114 for (i = 0; i < 256; i++) {
1115 /* p(X)=i is a small polynomial of weight <= 8 */
1116 for (b = 0; b < 4; b++) {
1117 /* we want to compute (p(X).X^(8*b+deg(g))) mod g(X) */
1118 tab = bch->mod8_tab + (b*256+i)*l;
1119 data = i << (8*b);
1120 while (data) {
1121 d = deg(data);
1122 /* subtract X^d.g(X) from p(X).X^(8*b+deg(g)) */
1123 data ^= g[0] >> (31-d);
1124 for (j = 0; j < ecclen; j++) {
1125 hi = (d < 31) ? g[j] << (d+1) : 0;
1126 lo = (j+1 < plen) ?
1127 g[j+1] >> (31-d) : 0;
1128 tab[j] ^= hi|lo;
1129 }
1130 }
1131 }
1132 }
1133}
1134
1135/*
1136 * build a base for factoring degree 2 polynomials
1137 */
1138static int build_deg2_base(struct bch_control *bch)
1139{
1140 const int m = GF_M(bch);
1141 int i, j, r;
1142 unsigned int sum, x, y, remaining, ak = 0, xi[m];
1143
1144 /* find k s.t. Tr(a^k) = 1 and 0 <= k < m */
1145 for (i = 0; i < m; i++) {
1146 for (j = 0, sum = 0; j < m; j++)
1147 sum ^= a_pow(bch, i*(1 << j));
1148
1149 if (sum) {
1150 ak = bch->a_pow_tab[i];
1151 break;
1152 }
1153 }
1154 /* find xi, i=0..m-1 such that xi^2+xi = a^i+Tr(a^i).a^k */
1155 remaining = m;
1156 memset(xi, 0, sizeof(xi));
1157
1158 for (x = 0; (x <= GF_N(bch)) && remaining; x++) {
1159 y = gf_sqr(bch, x)^x;
1160 for (i = 0; i < 2; i++) {
1161 r = a_log(bch, y);
1162 if (y && (r < m) && !xi[r]) {
1163 bch->xi_tab[r] = x;
1164 xi[r] = 1;
1165 remaining--;
1166 dbg("x%d = %x\n", r, x);
1167 break;
1168 }
1169 y ^= ak;
1170 }
1171 }
1172 /* should not happen but check anyway */
1173 return remaining ? -1 : 0;
1174}
1175
1176static void *bch_alloc(size_t size, int *err)
1177{
1178 void *ptr;
1179
1180 ptr = kmalloc(size, GFP_KERNEL);
1181 if (ptr == NULL)
1182 *err = 1;
1183 return ptr;
1184}
1185
1186/*
1187 * compute generator polynomial for given (m,t) parameters.
1188 */
1189static uint32_t *compute_generator_polynomial(struct bch_control *bch)
1190{
1191 const unsigned int m = GF_M(bch);
1192 const unsigned int t = GF_T(bch);
1193 int n, err = 0;
1194 unsigned int i, j, nbits, r, word, *roots;
1195 struct gf_poly *g;
1196 uint32_t *genpoly;
1197
1198 g = bch_alloc(GF_POLY_SZ(m*t), &err);
1199 roots = bch_alloc((bch->n+1)*sizeof(*roots), &err);
1200 genpoly = bch_alloc(DIV_ROUND_UP(m*t+1, 32)*sizeof(*genpoly), &err);
1201
1202 if (err) {
1203 kfree(genpoly);
1204 genpoly = NULL;
1205 goto finish;
1206 }
1207
1208 /* enumerate all roots of g(X) */
1209 memset(roots , 0, (bch->n+1)*sizeof(*roots));
1210 for (i = 0; i < t; i++) {
1211 for (j = 0, r = 2*i+1; j < m; j++) {
1212 roots[r] = 1;
1213 r = mod_s(bch, 2*r);
1214 }
1215 }
1216 /* build generator polynomial g(X) */
1217 g->deg = 0;
1218 g->c[0] = 1;
1219 for (i = 0; i < GF_N(bch); i++) {
1220 if (roots[i]) {
1221 /* multiply g(X) by (X+root) */
1222 r = bch->a_pow_tab[i];
1223 g->c[g->deg+1] = 1;
1224 for (j = g->deg; j > 0; j--)
1225 g->c[j] = gf_mul(bch, g->c[j], r)^g->c[j-1];
1226
1227 g->c[0] = gf_mul(bch, g->c[0], r);
1228 g->deg++;
1229 }
1230 }
1231 /* store left-justified binary representation of g(X) */
1232 n = g->deg+1;
1233 i = 0;
1234
1235 while (n > 0) {
1236 nbits = (n > 32) ? 32 : n;
1237 for (j = 0, word = 0; j < nbits; j++) {
1238 if (g->c[n-1-j])
1239 word |= 1u << (31-j);
1240 }
1241 genpoly[i++] = word;
1242 n -= nbits;
1243 }
1244 bch->ecc_bits = g->deg;
1245
1246finish:
1247 kfree(g);
1248 kfree(roots);
1249
1250 return genpoly;
1251}
1252
1253/**
1254 * init_bch - initialize a BCH encoder/decoder
1255 * @m: Galois field order, should be in the range 5-15
1256 * @t: maximum error correction capability, in bits
1257 * @prim_poly: user-provided primitive polynomial (or 0 to use default)
1258 *
1259 * Returns:
1260 * a newly allocated BCH control structure if successful, NULL otherwise
1261 *
1262 * This initialization can take some time, as lookup tables are built for fast
1263 * encoding/decoding; make sure not to call this function from a time critical
1264 * path. Usually, init_bch() should be called on module/driver init and
1265 * free_bch() should be called to release memory on exit.
1266 *
1267 * You may provide your own primitive polynomial of degree @m in argument
1268 * @prim_poly, or let init_bch() use its default polynomial.
1269 *
1270 * Once init_bch() has successfully returned a pointer to a newly allocated
1271 * BCH control structure, ecc length in bytes is given by member @ecc_bytes of
1272 * the structure.
1273 */
1274struct bch_control *init_bch(int m, int t, unsigned int prim_poly)
1275{
1276 int err = 0;
1277 unsigned int i, words;
1278 uint32_t *genpoly;
1279 struct bch_control *bch = NULL;
1280
1281 const int min_m = 5;
1282 const int max_m = 15;
1283
1284 /* default primitive polynomials */
1285 static const unsigned int prim_poly_tab[] = {
1286 0x25, 0x43, 0x83, 0x11d, 0x211, 0x409, 0x805, 0x1053, 0x201b,
1287 0x402b, 0x8003,
1288 };
1289
1290#if defined(CONFIG_BCH_CONST_PARAMS)
1291 if ((m != (CONFIG_BCH_CONST_M)) || (t != (CONFIG_BCH_CONST_T))) {
1292 printk(KERN_ERR "bch encoder/decoder was configured to support "
1293 "parameters m=%d, t=%d only!\n",
1294 CONFIG_BCH_CONST_M, CONFIG_BCH_CONST_T);
1295 goto fail;
1296 }
1297#endif
1298 if ((m < min_m) || (m > max_m))
1299 /*
1300 * values of m greater than 15 are not currently supported;
1301 * supporting m > 15 would require changing table base type
1302 * (uint16_t) and a small patch in matrix transposition
1303 */
1304 goto fail;
1305
1306 /* sanity checks */
1307 if ((t < 1) || (m*t >= ((1 << m)-1)))
1308 /* invalid t value */
1309 goto fail;
1310
1311 /* select a primitive polynomial for generating GF(2^m) */
1312 if (prim_poly == 0)
1313 prim_poly = prim_poly_tab[m-min_m];
1314
1315 bch = kzalloc(sizeof(*bch), GFP_KERNEL);
1316 if (bch == NULL)
1317 goto fail;
1318
1319 bch->m = m;
1320 bch->t = t;
1321 bch->n = (1 << m)-1;
1322 words = DIV_ROUND_UP(m*t, 32);
1323 bch->ecc_bytes = DIV_ROUND_UP(m*t, 8);
1324 bch->a_pow_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_pow_tab), &err);
1325 bch->a_log_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_log_tab), &err);
1326 bch->mod8_tab = bch_alloc(words*1024*sizeof(*bch->mod8_tab), &err);
1327 bch->ecc_buf = bch_alloc(words*sizeof(*bch->ecc_buf), &err);
1328 bch->ecc_buf2 = bch_alloc(words*sizeof(*bch->ecc_buf2), &err);
1329 bch->xi_tab = bch_alloc(m*sizeof(*bch->xi_tab), &err);
1330 bch->syn = bch_alloc(2*t*sizeof(*bch->syn), &err);
1331 bch->cache = bch_alloc(2*t*sizeof(*bch->cache), &err);
1332 bch->elp = bch_alloc((t+1)*sizeof(struct gf_poly_deg1), &err);
1333
1334 for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
1335 bch->poly_2t[i] = bch_alloc(GF_POLY_SZ(2*t), &err);
1336
1337 if (err)
1338 goto fail;
1339
1340 err = build_gf_tables(bch, prim_poly);
1341 if (err)
1342 goto fail;
1343
1344 /* use generator polynomial for computing encoding tables */
1345 genpoly = compute_generator_polynomial(bch);
1346 if (genpoly == NULL)
1347 goto fail;
1348
1349 build_mod8_tables(bch, genpoly);
1350 kfree(genpoly);
1351
1352 err = build_deg2_base(bch);
1353 if (err)
1354 goto fail;
1355
1356 return bch;
1357
1358fail:
1359 free_bch(bch);
1360 return NULL;
1361}
1362EXPORT_SYMBOL_GPL(init_bch);
1363
1364/**
1365 * free_bch - free the BCH control structure
1366 * @bch: BCH control structure to release
1367 */
1368void free_bch(struct bch_control *bch)
1369{
1370 unsigned int i;
1371
1372 if (bch) {
1373 kfree(bch->a_pow_tab);
1374 kfree(bch->a_log_tab);
1375 kfree(bch->mod8_tab);
1376 kfree(bch->ecc_buf);
1377 kfree(bch->ecc_buf2);
1378 kfree(bch->xi_tab);
1379 kfree(bch->syn);
1380 kfree(bch->cache);
1381 kfree(bch->elp);
1382
1383 for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
1384 kfree(bch->poly_2t[i]);
1385
1386 kfree(bch);
1387 }
1388}
1389EXPORT_SYMBOL_GPL(free_bch);
1390
1391MODULE_LICENSE("GPL");
1392MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
1393MODULE_DESCRIPTION("Binary BCH encoder/decoder");
generated by cgit v1.2.3 (git 2.39.1) at 2024-09-22 17:29:52 +0000