1 /*
2 * This includes forward error correction code based on Vandermonde matrices
3 * 980624
4 * (C) 1997-98 Luigi Rizzo (luigi@iet.unipi.it)
5 *
6 * Portions derived from code by Phil Karn (karn@ka9q.ampr.org),
7 * Robert Morelos-Zaragoza (robert@spectra.eng.hawaii.edu) and Hari
8 * Thirumoorthy (harit@spectra.eng.hawaii.edu), Aug 1995
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 *
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above
17 * copyright notice, this list of conditions and the following
18 * disclaimer in the documentation and/or other materials
19 * provided with the distribution.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
23 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
24 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS
25 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
26 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
27 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
28 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
29 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
30 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
32 * OF SUCH DAMAGE.
33 */
34
35
36 #include "normEncoderRS16.h"
37 #include "protoDebug.h"
38 #ifdef SIMULATE
39 #include "normMessage.h"
40 #endif // SIMULATE
41
42 /*
43 * The first part of the file here implements linear algebra in GF.
44 *
45 * gf is the type used to store an element of the Galois Field.
46 * Must constain at least GF_BITS bits.
47 *
48 * Note: unsigned char will work up to GF(256) but int seems to run
49 * faster on the Pentium. We use int whenever have to deal with an
50 * index, since they are generally faster.
51 */
52
53 #define GF_BITS 16 // 16-bit RS code
54 #if (GF_BITS < 2 && GF_BITS > 16)
55 #error "GF_BITS must be 2 .. 16"
56 #endif
57 #if (GF_BITS <= 8)
58 typedef UINT8 gf;
59 #else
60 typedef UINT16 gf;
61 #endif
62 #define GF_SIZE ((1 << GF_BITS) - 1) // powers of alpha
63
64
65 /*
66 * Primitive polynomials - see Lin & Costello, Appendix A,
67 * and Lee & Messerschmitt, p. 453.
68 */
69
70 static const char *allPp[] =
71 { // GF_BITS Polynomial
72 NULL, // 0 no code
73 NULL, // 1 no code
74 "111", // 2 1+x+x^2
75 "1101", // 3 1+x+x^3
76 "11001", // 4 1+x+x^4
77 "101001", // 5 1+x^2+x^5
78 "1100001", // 6 1+x+x^6
79 "10010001", // 7 1 + x^3 + x^7
80 "101110001", // 8 1+x^2+x^3+x^4+x^8
81 "1000100001", // 9 1+x^4+x^9
82 "10010000001", // 10 1+x^3+x^10
83 "101000000001", // 11 1+x^2+x^11
84 "1100101000001", // 12 1+x+x^4+x^6+x^12
85 "11011000000001", // 13 1+x+x^3+x^4+x^13
86 "110000100010001", // 14 1+x+x^6+x^10+x^14
87 "1100000000000001", // 15 1+x+x^15
88 "11010000000010001" // 16 1+x+x^3+x^12+x^16
89 };
90
91
92 /*
93 * To speed up computations, we have tables for logarithm, exponent
94 * and inverse of a number. If GF_BITS <= 8, we use a table for
95 * multiplication as well (it takes 64K, no big deal even on a PDA,
96 * especially because it can be pre-initialized an put into a ROM!),
97 * otherwhise we use a table of logarithms.
98 * In any case the macro gf_mul(x,y) takes care of multiplications.
99 */
100
101 static gf gf_exp[2*GF_SIZE]; // index->poly form conversion table
102 static int gf_log[GF_SIZE + 1]; // Poly->index form conversion table
103 static gf inverse[GF_SIZE+1]; // inverse of field elem.
104 // inv[\alpha**i]=\alpha**(GF_SIZE-i-1)
105
106 // modnn(x) computes x % GF_SIZE, where GF_SIZE is 2**GF_BITS - 1,
107 // without a slow divide.
modnn(int x)108 static inline gf modnn(int x)
109 {
110 while (x >= GF_SIZE)
111 {
112 x -= GF_SIZE;
113 x = (x >> GF_BITS) + (x & GF_SIZE);
114 }
115 return x;
116 } // end modnn()
117
118 #define SWAP(a,b,t) {t tmp; tmp=a; a=b; b=tmp;}
119
120 /*
121 * gf_mul(x,y) multiplies two numbers. If GF_BITS<=8, it is much
122 * faster to use a multiplication table.
123 *
124 * USE_GF_MULC, GF_MULC0(c) and GF_ADDMULC(x) can be used when multiplying
125 * many numbers by the same constant. In this case the first
126 * call sets the constant, and others perform the multiplications.
127 * A value related to the multiplication is held in a local variable
128 * declared with USE_GF_MULC . See usage in addmul1().
129 */
130 #if (GF_BITS <= 8)
131
132 static gf gf_mul_table[GF_SIZE + 1][GF_SIZE + 1];
133
134 #define gf_mul(x,y) gf_mul_table[x][y]
135 #define USE_GF_MULC register gf * __gf_mulc_
136 #define GF_MULC0(c) __gf_mulc_ = gf_mul_table[c]
137 #define GF_ADDMULC(dst, x) dst ^= __gf_mulc_[x]
138
init_mul_table()139 static void init_mul_table()
140 {
141 for (int i = 0; i <= GF_SIZE; i++)
142 {
143 for (int j = 0; j <= GF_SIZE; j++)
144 gf_mul_table[i][j] = gf_exp[modnn(gf_log[i] + gf_log[j]) ] ;
145 }
146 for (int j = 0; j <= GF_SIZE; j++)
147 gf_mul_table[0][j] = gf_mul_table[j][0] = 0;
148 }
149
150 #else /* GF_BITS > 8 */
151
gf_mul(int x,int y)152 inline gf gf_mul(int x, int y)
153 {
154 if ((0 == x) || (0 == y)) return 0;
155 return gf_exp[gf_log[x] + gf_log[y] ] ;
156 }
157
158 #define init_mul_table()
159 #define USE_GF_MULC register gf * __gf_mulc_
160 #define GF_MULC0(c) __gf_mulc_ = &gf_exp[ gf_log[c] ]
161 #define GF_ADDMULC(dst, x) { if (x) dst ^= __gf_mulc_[ gf_log[x] ] ; }
162
163 #endif // if/else (GF_BITS <= 8)
164
165 /*
166 * Generate GF(2**m) from the irreducible polynomial p(X) in p[0]..p[m]
167 * Lookup tables:
168 * index->polynomial form gf_exp[] contains j= \alpha^i;
169 * polynomial form -> index form gf_log[ j = \alpha^i ] = i
170 * \alpha=x is the primitive element of GF(2^m)
171 *
172 * For efficiency, gf_exp[] has size 2*GF_SIZE, so that a simple
173 * multiplication of two numbers can be resolved without calling modnn
174 */
175
176 #define NEW_GF_MATRIX(rows, cols) (new gf[rows*cols])
177
178 /*
179 * initialize the data structures used for computations in GF.
180 */
generate_gf()181 static void generate_gf()
182 {
183 const char *Pp = allPp[GF_BITS] ;
184
185 gf mask = 1; /* x ** 0 = 1 */
186 gf_exp[GF_BITS] = 0; /* will be updated at the end of the 1st loop */
187 /*
188 * first, generate the (polynomial representation of) powers of \alpha,
189 * which are stored in gf_exp[i] = \alpha ** i .
190 * At the same time build gf_log[gf_exp[i]] = i .
191 * The first GF_BITS powers are simply bits shifted to the left.
192 */
193 for (int i = 0; i < GF_BITS; i++, mask <<= 1 )
194 {
195 gf_exp[i] = mask;
196 gf_log[gf_exp[i]] = i;
197 /*
198 * If Pp[i] == 1 then \alpha ** i occurs in poly-repr
199 * gf_exp[GF_BITS] = \alpha ** GF_BITS
200 */
201 if ( Pp[i] == '1' )
202 gf_exp[GF_BITS] ^= mask;
203 }
204 /*
205 * now gf_exp[GF_BITS] = \alpha ** GF_BITS is complete, so can als
206 * compute its inverse.
207 */
208 gf_log[gf_exp[GF_BITS]] = GF_BITS;
209 /*
210 * Poly-repr of \alpha ** (i+1) is given by poly-repr of
211 * \alpha ** i shifted left one-bit and accounting for any
212 * \alpha ** GF_BITS term that may occur when poly-repr of
213 * \alpha ** i is shifted.
214 */
215 mask = 1 << (GF_BITS - 1 ) ;
216 for (int i = GF_BITS + 1; i < GF_SIZE; i++)
217 {
218 if (gf_exp[i - 1] >= mask)
219 gf_exp[i] = gf_exp[GF_BITS] ^ ((gf_exp[i - 1] ^ mask) << 1);
220 else
221 gf_exp[i] = gf_exp[i - 1] << 1;
222 gf_log[gf_exp[i]] = i;
223 }
224 /*
225 * log(0) is not defined, so use a special value
226 */
227 gf_log[0] = GF_SIZE ;
228 /* set the extended gf_exp values for fast multiply */
229 for (int i = 0 ; i < GF_SIZE ; i++)
230 gf_exp[i + GF_SIZE] = gf_exp[i] ;
231
232 /*
233 * again special cases. 0 has no inverse. This used to
234 * be initialized to GF_SIZE, but it should make no difference
235 * since noone is supposed to read from here.
236 */
237 inverse[0] = 0 ;
238 inverse[1] = 1;
239 for (int i = 2; i <= GF_SIZE; i++)
240 inverse[i] = gf_exp[GF_SIZE-gf_log[i]];
241 } // end generate_gf()
242
243
244 /*
245 * Various linear algebra operations that i use often.
246 */
247
248 /*
249 * addmul() computes dst[] = dst[] + c * src[]
250 * This is used often, so better optimize it! Currently the loop is
251 * unrolled 16 times, a good value for 486 and pentium-class machines.
252 * The case c=0 is also optimized, whereas c=1 is not. These
253 * calls are unfrequent in my typical apps so I did not bother.
254 *
255 * Note that gcc on
256 */
257 #define addmul(dst, src, c, sz) \
258 if (c != 0) addmul1(dst, src, c, sz)
259 #define UNROLL 16 /* 1, 4, 8, 16 */
260
addmul1(gf * dst1,gf * src1,gf c,int sz)261 static void addmul1(gf* dst1, gf* src1, gf c, int sz)
262 {
263 USE_GF_MULC ;
264 register gf* dst = dst1;
265 register gf* src = src1 ;
266 gf* lim = &dst[sz - UNROLL + 1] ;
267
268 GF_MULC0(c) ;
269
270 #if (UNROLL > 1) /* unrolling by 8/16 is quite effective on the pentium */
271 for (; dst < lim ; dst += UNROLL, src += UNROLL )
272 {
273 GF_ADDMULC( dst[0] , src[0] );
274 GF_ADDMULC( dst[1] , src[1] );
275 GF_ADDMULC( dst[2] , src[2] );
276 GF_ADDMULC( dst[3] , src[3] );
277 #if (UNROLL > 4)
278 GF_ADDMULC( dst[4] , src[4] );
279 GF_ADDMULC( dst[5] , src[5] );
280 GF_ADDMULC( dst[6] , src[6] );
281 GF_ADDMULC( dst[7] , src[7] );
282 #endif
283 #if (UNROLL > 8)
284 GF_ADDMULC( dst[8] , src[8] );
285 GF_ADDMULC( dst[9] , src[9] );
286 GF_ADDMULC( dst[10] , src[10] );
287 GF_ADDMULC( dst[11] , src[11] );
288 GF_ADDMULC( dst[12] , src[12] );
289 GF_ADDMULC( dst[13] , src[13] );
290 GF_ADDMULC( dst[14] , src[14] );
291 GF_ADDMULC( dst[15] , src[15] );
292 #endif
293 }
294 #endif
295 lim += UNROLL - 1 ;
296 for (; dst < lim; dst++, src++ ) /* final components */
297 GF_ADDMULC( *dst , *src );
298 } // end addmul1()
299
300
301 // computes C = AB where A is n*k, B is k*m, C is n*m
matmul(gf * a,gf * b,gf * c,int n,int k,int m)302 static void matmul(gf* a, gf* b, gf* c, int n, int k, int m)
303 {
304 int row, col, i ;
305
306 for (row = 0; row < n ; row++)
307 {
308 for (col = 0; col < m ; col++)
309 {
310 gf* pa = &a[ row * k ];
311 gf* pb = &b[ col ];
312 gf acc = 0 ;
313 for (i = 0; i < k ; i++, pa++, pb += m)
314 acc ^= gf_mul( *pa, *pb ) ;
315 c[row * m + col] = acc ;
316 }
317 }
318 } // end matmul()
319
320
invert_vdm(gf * src,int k)321 static int invert_vdm(gf* src, int k)
322 {
323 gf t, xx;
324
325 if (k == 1)return 0; // degenerate case, matrix must be p^0 = 1
326
327 /*
328 * c holds the coefficient of P(x) = Prod (x - p_i), i=0..k-1
329 * b holds the coefficient for the matrix inversion
330 */
331 gf* c = NEW_GF_MATRIX(1, k);
332 gf* b = NEW_GF_MATRIX(1, k);
333 gf* p = NEW_GF_MATRIX(1, k);
334
335 int i, j;
336 for (j = 1, i = 0 ; i < k ; i++, j+=k )
337 {
338 c[i] = 0 ;
339 p[i] = src[j] ; /* p[i] */
340 }
341 /*
342 * construct coeffs. recursively. We know c[k] = 1 (implicit)
343 * and start P_0 = x - p_0, then at each stage multiply by
344 * x - p_i generating P_i = x P_{i-1} - p_i P_{i-1}
345 * After k steps we are done.
346 */
347 c[k-1] = p[0] ; /* really -p(0), but x = -x in GF(2^m) */
348 for (i = 1 ; i < k ; i++)
349 {
350 gf p_i = p[i] ; /* see above comment */
351 for (j = k - 1 - ( i - 1 ) ; j < k-1 ; j++ )
352 c[j] ^= gf_mul( p_i, c[j+1] ) ;
353 c[k-1] ^= p_i ;
354 }
355 for (int row = 0 ; row < k ; row++)
356 {
357 /*
358 * synthetic division etc.
359 */
360 xx = p[row] ;
361 t = 1 ;
362 b[k-1] = 1 ; /* this is in fact c[k] */
363 for (i = k - 2 ; i >= 0 ; i-- )
364 {
365 b[i] = c[i+1] ^ gf_mul(xx, b[i+1]) ;
366 t = gf_mul(xx, t) ^ b[i] ;
367 }
368 for (int col = 0 ; col < k ; col++ )
369 src[col*k + row] = gf_mul(inverse[t], b[col] );
370 }
371 delete[] c;
372 delete[] b;
373 delete[] p;
374 return 0 ;
375 } // end invert_vdm()
376
377
378 static bool fec_initialized = false;
init_fec()379 static void init_fec()
380 {
381 if (!fec_initialized)
382 {
383 generate_gf();
384 init_mul_table();
385 fec_initialized = true;
386 }
387 }
388
NormEncoderRS16()389 NormEncoderRS16::NormEncoderRS16()
390 : enc_matrix(NULL)
391 {
392 }
393
~NormEncoderRS16()394 NormEncoderRS16::~NormEncoderRS16()
395 {
396 Destroy();
397 }
398
Init(unsigned int numData,unsigned int numParity,UINT16 vecSizeMax)399 bool NormEncoderRS16::Init(unsigned int numData, unsigned int numParity, UINT16 vecSizeMax)
400 {
401 #ifdef SIMULATE
402 vecSizeMax = MIN(SIM_PAYLOAD_MAX, vecSizeMax);
403 #endif // SIMULATE
404 if ((numData + numParity) > GF_SIZE)
405 {
406 PLOG(PL_FATAL, "NormEncoderRS16::Init() error: numData/numParity exceeds code limits\n");
407 return false;
408 }
409
410 if (NULL != enc_matrix)
411 {
412 delete[] enc_matrix;
413 enc_matrix = NULL;
414 }
415 init_fec();
416 int n = numData + numParity;
417 int k = numData;
418 enc_matrix = (UINT8*)NEW_GF_MATRIX(n, k);
419 if (NULL != enc_matrix)
420 {
421 gf* tmpMatrix = NEW_GF_MATRIX(n, k);
422 if (NULL == tmpMatrix)
423 {
424 PLOG(PL_FATAL, "NormEncoderRS16::Init() error: new tmpMatrix error: %s\n", GetErrorString());
425 delete[] enc_matrix;
426 enc_matrix = NULL;
427 return false;
428 }
429 // Fill the matrix with powers of field elements, starting from 0.
430 // The first row is special, cannot be computed with exp. table.
431 tmpMatrix[0] = 1 ;
432 for (int col = 1; col < k ; col++)
433 tmpMatrix[col] = 0 ;
434 for (gf* p = tmpMatrix + k, row = 0; row < n-1 ; row++, p += k)
435 {
436 for (int col = 0 ; col < k ; col ++ )
437 p[col] = gf_exp[modnn(row*col)];
438 }
439
440
441 // Quick code to build systematic matrix: invert the top
442 // k*k vandermonde matrix, multiply right the bottom n-k rows
443 // by the inverse, and construct the identity matrix at the top.
444 invert_vdm(tmpMatrix, k); /* much faster than invert_mat */
445 matmul(tmpMatrix + k*k, tmpMatrix, ((gf*)enc_matrix) + k*k, n - k, k, k);
446 // the upper matrix is I so do not bother with a slow multiply
447 memset(enc_matrix, 0, k*k*sizeof(gf));
448 for (gf* p = (gf*)enc_matrix, col = 0 ; col < k ; col++, p += k+1 )
449 *p = 1 ;
450 delete[] tmpMatrix;
451 ndata = numData;
452 npar = numParity;
453 vector_size = vecSizeMax;
454 return true;
455 }
456 else
457 {
458 PLOG(PL_FATAL, "NormEncoderRS16::Init() error: new enc_matrix error: %s\n", GetErrorString());
459 return false;
460 }
461 } // end NormEncoderRS16::Init()
462
Destroy()463 void NormEncoderRS16::Destroy()
464 {
465 if (NULL != enc_matrix)
466 {
467 delete[] enc_matrix;
468 enc_matrix = NULL;
469 }
470 } // end NormEncoderRS16::Destroy()
471
Encode(unsigned int segmentId,const char * dataVector,char ** parityVectorList)472 void NormEncoderRS16::Encode(unsigned int segmentId, const char* dataVector, char** parityVectorList)
473 {
474 for (unsigned int i = 0; i < npar; i++)
475 {
476 // Update each parity vector
477 gf* fec = (gf*)parityVectorList[i];
478 gf* p = ((gf*)enc_matrix) + ((i+ndata)*ndata);
479 unsigned int nelements = (GF_BITS > 8) ? vector_size / 2 : vector_size;
480 addmul(fec, (gf*)dataVector, p[segmentId], nelements);
481 }
482 } // end NormEncoderRS16::Encode()
483
484
NormDecoderRS16()485 NormDecoderRS16::NormDecoderRS16()
486 : enc_matrix(NULL), dec_matrix(NULL),
487 parity_loc(NULL), inv_ndxc(NULL), inv_ndxr(NULL),
488 inv_pivt(NULL), inv_id_row(NULL), inv_temp_row(NULL)
489 {
490 }
491
~NormDecoderRS16()492 NormDecoderRS16::~NormDecoderRS16()
493 {
494 Destroy();
495 }
496
Destroy()497 void NormDecoderRS16::Destroy()
498 {
499 if (NULL != enc_matrix)
500 {
501 delete[] enc_matrix;
502 enc_matrix = NULL;
503 }
504 if (NULL != dec_matrix)
505 {
506 delete[] dec_matrix;
507 dec_matrix = NULL;
508 }
509 if (NULL != parity_loc)
510 {
511 delete[] parity_loc;
512 parity_loc = NULL;
513 }
514 if (NULL != inv_ndxc)
515 {
516 delete[] inv_ndxc;
517 inv_ndxc = NULL;
518 }
519 if (NULL != inv_ndxr)
520 {
521 delete[] inv_ndxr;
522 inv_ndxr = NULL;
523 }
524 if (NULL != inv_pivt)
525 {
526 delete[] inv_pivt;
527 inv_pivt = NULL;
528 }
529 if (NULL != inv_id_row)
530 {
531 delete[] inv_id_row;
532 inv_id_row = NULL;
533 }
534 if (NULL != inv_temp_row)
535 {
536 delete[] inv_temp_row;
537 inv_temp_row = NULL;
538 }
539 } // end NormDecoderRS16::Destroy()
540
Init(unsigned int numData,unsigned int numParity,UINT16 vecSizeMax)541 bool NormDecoderRS16::Init(unsigned int numData, unsigned int numParity, UINT16 vecSizeMax)
542 {
543 #ifdef SIMULATE
544 vecSizeMax = MIN(SIM_PAYLOAD_MAX, vecSizeMax);
545 #endif // SIMULATE
546 if ((numData + numParity) > GF_SIZE)
547 {
548 PLOG(PL_FATAL, "NormEncoderRS16::Init() error: numData/numParity exceeds code limits\n");
549 return false;
550 }
551
552 init_fec();
553 Destroy();
554
555 int n = numData + numParity;
556 int k = numData;
557
558 if (NULL == (inv_ndxc = new unsigned int[k]))
559 {
560 PLOG(PL_FATAL, "NormDecoderRS16::Init() new inv_indxc error: %s\n", GetErrorString());
561 Destroy();
562 return false;
563 }
564
565 if (NULL == (inv_ndxr = new unsigned int[k]))
566 {
567 PLOG(PL_FATAL, "NormDecoderRS16::Init() new inv_inv_ndxr error: %s\n", GetErrorString());
568 Destroy();
569 return false;
570 }
571
572 if (NULL == (inv_pivt = new unsigned int[k]))
573 {
574 PLOG(PL_FATAL, "NormDecoderRS16::Init() new inv_pivt error: %s\n", GetErrorString());
575 Destroy();
576 return false;
577 }
578
579 if (NULL == (inv_id_row = (UINT8*)NEW_GF_MATRIX(1, k)))
580 {
581 PLOG(PL_FATAL, "NormDecoderRS16::Init() new inv_id_row error: %s\n", GetErrorString());
582 Destroy();
583 return false;
584 }
585
586 if (NULL == (inv_temp_row = (UINT8*)NEW_GF_MATRIX(1, k)))
587 {
588 PLOG(PL_FATAL, "NormDecoderRS16::Init() new inv_temp_row error: %s\n", GetErrorString());
589 Destroy();
590 return false;
591 }
592
593 if (NULL == (parity_loc = new unsigned int[numParity]))
594 {
595 PLOG(PL_FATAL, "NormDecoderRS16::Init() error: new parity_loc error: %s\n", GetErrorString());
596 Destroy();
597 return false;
598 }
599
600 if (NULL == (dec_matrix = (UINT8*)NEW_GF_MATRIX(k, k)))
601 {
602 PLOG(PL_FATAL, "NormDecoderRS16::Init() error: new dec_matrix error: %s\n", GetErrorString());
603 Destroy();
604 return false;
605 }
606
607 if (NULL == (enc_matrix = (UINT8*)NEW_GF_MATRIX(n, k)))
608 {
609 PLOG(PL_FATAL, "NormDecoderRS16::Init() error: new enc_matrix error: %s\n", GetErrorString());
610 Destroy();
611 return false;
612 }
613
614 gf* tmpMatrix = NEW_GF_MATRIX(n, k);
615 if (NULL == tmpMatrix)
616 {
617 PLOG(PL_FATAL, "NormDecoderRS16::Init() error: new tmpMatrix error: %s\n", GetErrorString());
618 delete[] enc_matrix;
619 enc_matrix = NULL;
620 return false;
621 }
622 // Fill the matrix with powers of field elements, starting from 0.
623 // The first row is special, cannot be computed with exp. table.
624 tmpMatrix[0] = 1 ;
625 for (int col = 1; col < k ; col++)
626 tmpMatrix[col] = 0 ;
627 for (gf* p = tmpMatrix + k, row = 0; row < n-1 ; row++, p += k)
628 {
629 for (int col = 0 ; col < k ; col ++ )
630 p[col] = gf_exp[modnn(row*col)];
631 }
632
633 // Quick code to build systematic matrix: invert the top
634 // k*k vandermonde matrix, multiply right the bottom n-k rows
635 // by the inverse, and construct the identity matrix at the top.
636 invert_vdm(tmpMatrix, k); /* much faster than invert_mat */
637 matmul(tmpMatrix + k*k, tmpMatrix, ((gf*)enc_matrix) + k*k, n - k, k, k);
638 // the upper matrix is I so do not bother with a slow multiply
639 memset(enc_matrix, 0, k*k*sizeof(gf));
640 for (gf* p = (gf*)enc_matrix, col = 0 ; col < k ; col++, p += k+1 )
641 *p = 1 ;
642 delete[] tmpMatrix;
643 ndata = numData;
644 npar = numParity;
645 vector_size = vecSizeMax;
646 return true;
647 } // end NormDecoderRS16::Init()
648
649
Decode(char ** vectorList,unsigned int numData,unsigned int erasureCount,unsigned int * erasureLocs)650 int NormDecoderRS16::Decode(char** vectorList, unsigned int numData, unsigned int erasureCount, unsigned int* erasureLocs)
651 {
652 unsigned int bsz = ndata + npar;
653 // 1) Build decoding matrix for the given set of segments & erasures
654 unsigned int nextErasure = 0;
655 unsigned int ne = 0;
656 unsigned int sourceErasureCount = 0;
657 unsigned int parityCount = 0;
658 for (unsigned int i = 0; i < bsz; i++)
659 {
660 if (i < numData)
661 {
662 if ((nextErasure < erasureCount) && (i == erasureLocs[nextErasure]))
663 {
664 nextErasure++;
665 sourceErasureCount++;
666 }
667 else
668 {
669 // set identity row for segments we have
670 gf* p = ((gf*)dec_matrix) + ndata*i;
671 memset(p, 0, ndata*sizeof(gf));
672 p[i] = 1;
673 }
674 }
675 else if (i < ndata)
676 {
677 // set identity row for assumed zero segments (shortened code)
678 gf* p = ((gf*)dec_matrix) + ndata*i;
679 memset(p, 0, ndata*sizeof(gf));
680 p[i] = 1;
681 // Also keep track of where the non-erased parity segment are
682 // for the shortened code
683 if ((nextErasure < erasureCount) && (i == erasureLocs[nextErasure]))
684 {
685 nextErasure++;
686 }
687 else if (parityCount < sourceErasureCount)
688 {
689 parity_loc[parityCount++] = i;
690 // Copy appropriate enc_matric parity row to dec_matrix erasureRow
691 gf* p = ((gf*)dec_matrix) + ndata*erasureLocs[ne++];
692 memcpy(p, ((gf*)enc_matrix) + (ndata-numData+i)*ndata, ndata*sizeof(gf));
693 }
694
695 }
696 else if (parityCount < sourceErasureCount)
697 {
698 if ((nextErasure < erasureCount) && (i == erasureLocs[nextErasure]))
699 {
700 nextErasure++;
701 }
702 else
703 {
704 ASSERT(parityCount < npar);
705 parity_loc[parityCount++] = i;
706 // Copy appropriate enc_matric parity row to dec_matrix erasureRow
707 gf* p = ((gf*)dec_matrix) + ndata*erasureLocs[ne++];
708 memcpy(p, ((gf*)enc_matrix) + (ndata-numData+i)*ndata, ndata*sizeof(gf));
709 }
710 }
711 else
712 {
713 break;
714 }
715
716 }
717 ASSERT(ne == sourceErasureCount);
718 // 2) Invert the decoding matrix
719 if (!InvertDecodingMatrix())
720 {
721 PLOG(PL_FATAL, "NormDecoderRS16::Decode() error: couldn't invert dec_matrix (numData:%d erasureCount:%d) ?!\n", numData, erasureCount);
722 return 0;
723 }
724
725 // 3) Decode
726 for (unsigned int e = 0; e < erasureCount; e++)
727 {
728 // Calculate missing segments (erasures) using dec_matrix and non-erasures
729 unsigned int row = erasureLocs[e];
730 if (row >= numData) break; // don't bother filling in parity segments
731 unsigned int col = 0;
732 unsigned int nextErasure = 0;
733 unsigned int nelements = (GF_BITS > 8) ? vector_size/2 : vector_size;
734 for (unsigned int i = 0; i < numData; i++)
735 {
736 if ((nextErasure < erasureCount) && (i == erasureLocs[nextErasure]))
737 {
738 // Use parity segments in place of erased vector in decoding
739 addmul((gf*)vectorList[row], (gf*)vectorList[parity_loc[nextErasure]], ((gf*)dec_matrix)[row*ndata + col], nelements);
740 col++;
741 nextErasure++; // point to next erasure
742 }
743 else if (i < numData)
744 {
745 addmul((gf*)vectorList[row], (gf*)vectorList[i], ((gf*)dec_matrix)[row*ndata + col], nelements);
746 col++;
747 }
748 else
749 {
750 ASSERT(0);
751 }
752 }
753 }
754 return erasureCount ;
755 } // end NormDecoderRS16::Decode()
756
757
758
759 /*
760 * NormDecoderRS16::InvertDecodingMatrix() takes a matrix and produces its inverse
761 * k is the size of the matrix. (Gauss-Jordan, adapted from Numerical Recipes in C)
762 * Return non-zero if singular.
763 */
InvertDecodingMatrix()764 bool NormDecoderRS16::InvertDecodingMatrix()
765 {
766 gf* src = (gf*)dec_matrix;
767 unsigned int k = ndata;
768
769 memset(inv_id_row, 0, k*sizeof(gf));
770 // inv_pivt marks elements already used as pivots.
771 memset(inv_pivt, 0, k*sizeof(unsigned int));
772
773 for (unsigned int col = 0; col < k ; col++)
774 {
775 /*
776 * Zeroing column 'col', look for a non-zero element.
777 * First try on the diagonal, if it fails, look elsewhere.
778 */
779 int irow = -1;
780 int icol = -1 ;
781 if (inv_pivt[col] != 1 && src[col*k + col] != 0)
782 {
783 irow = col ;
784 icol = col ;
785 goto found_piv ;
786 }
787 for (int row = 0 ; row < k ; row++)
788 {
789 if (inv_pivt[row] != 1)
790 {
791 for (unsigned int ix = 0 ; ix < k ; ix++)
792 {
793 if (inv_pivt[ix] == 0)
794 {
795 if (src[row*k + ix] != 0)
796 {
797 irow = row ;
798 icol = ix ;
799 goto found_piv ;
800 }
801 }
802 else if (inv_pivt[ix] > 1)
803 {
804 PLOG(PL_FATAL, "NormDecoderRS16::InvertDecodingMatrix() error: singular matrix!\n");
805 return false;
806 }
807 }
808 }
809 }
810 if (icol == -1)
811 {
812 PLOG(PL_FATAL, "NormDecoderRS16::InvertDecodingMatrix() error: pivot not found!\n");
813 return false;
814 }
815 found_piv:
816 ++(inv_pivt[icol]) ;
817 /*
818 * swap rows irow and icol, so afterwards the diagonal
819 * element will be correct. Rarely done, not worth
820 * optimizing.
821 */
822 if (irow != icol)
823 {
824 for (unsigned int ix = 0 ; ix < k ; ix++ )
825 SWAP(src[irow*k + ix], src[icol*k + ix], gf);
826 }
827 inv_ndxr[col] = irow ;
828 inv_ndxc[col] = icol ;
829 gf* pivotRow = &src[icol*k] ;
830 gf c = pivotRow[icol] ;
831 if (c == 0)
832 {
833 PLOG(PL_FATAL, "NormDecoderRS16::InvertDecodingMatrix() error: singular matrix!\n");
834 return false;
835 }
836 if (c != 1 ) /* otherwhise this is a NOP */
837 {
838 /*
839 * this is done often , but optimizing is not so
840 * fruitful, at least in the obvious ways (unrolling)
841 */
842 c = inverse[ c ] ;
843 pivotRow[icol] = 1 ;
844 for (unsigned int ix = 0 ; ix < k ; ix++ )
845 pivotRow[ix] = gf_mul(c, pivotRow[ix] );
846 }
847 /*
848 * from all rows, remove multiples of the selected row
849 * to zero the relevant entry (in fact, the entry is not zero
850 * because we know it must be zero).
851 * (Here, if we know that the pivot_row is the identity,
852 * we can optimize the addmul).
853 */
854 inv_id_row[icol] = 1;
855 if (0 != memcmp(pivotRow, inv_id_row, k*sizeof(gf)))
856 {
857 for (gf* p = src, ix = 0 ; ix < k ; ix++, p += k )
858 {
859 if (ix != icol)
860 {
861 c = p[icol] ;
862 p[icol] = 0 ;
863 addmul(p, pivotRow, c, k );
864 }
865 }
866 }
867 inv_id_row[icol] = 0;
868 } // end for (col = 0; col < k ; col++)
869
870 for (int col = k - 1 ; col >= 0 ; col-- )
871 {
872 if (inv_ndxr[col] >= k)
873 {
874 PLOG(PL_ERROR, "NormDecoderRS16::InvertDecodingMatrix() error: AARGH, inv_ndxr[col] %d\n", inv_ndxr[col]);
875 }
876 else if (inv_ndxc[col] >= k)
877 {
878 PLOG(PL_ERROR, "NormDecoderRS16::InvertDecodingMatrix() error: AARGH, indxc[col] %d\n", inv_ndxc[col]);
879 }
880 else if (inv_ndxr[col] != inv_ndxc[col] )
881 {
882 for (int row = 0 ; row < k ; row++ )
883 SWAP( src[row*k + inv_ndxr[col]], src[row*k + inv_ndxc[col]], gf) ;
884 }
885 }
886 return true;
887 } // end NormDecoderRS16::InvertDecodingMatrix()
888
889