git.zerfleddert.de Git - proxmark3-svn/blob - armsrc/pcf7931.c

   1 #include "proxmark3.h"
   2 #include "apps.h"
   3 #include "usb_cdc.h"
   4 #include "lfsampling.h"
   5 #include "pcf7931.h"
   6 #include "util.h"
   7 #include "string.h"
   8 #include "fpgaloader.h"
   9
  10 #define T0_PCF 8 //period for the pcf7931 in us
  11 #define ALLOC 16
  12
  13 size_t DemodPCF7931(uint8_t **outBlocks) {
  14         uint8_t bits[256] = {0x00};
  15         uint8_t blocks[8][16];
  16         uint8_t *dest = BigBuf_get_addr();
  17
  18         int GraphTraceLen = BigBuf_max_traceLen();
  19         if (GraphTraceLen > 18000)
  20                 GraphTraceLen = 18000;
  21
  22         int i, j, lastval, bitidx, half_switch;
  23         int clock = 64;
  24         int tolerance = clock / 8;
  25         int pmc, block_done;
  26         int lc, warnings = 0;
  27         size_t num_blocks = 0;
  28         int lmin=128, lmax=128;
  29         uint8_t dir;
  30         //clear read buffer
  31         BigBuf_Clear_keep_EM();
  32
  33         LFSetupFPGAForADC(95, true);
  34         DoAcquisition_default(0, true);
  35
  36         lmin = 64;
  37         lmax = 192;
  38
  39         i = 2;
  40
  41         /* Find first local max/min */
  42         if(dest[1] > dest[0]) {
  43                 while(i < GraphTraceLen) {
  44                         if( !(dest[i] > dest[i-1]) && dest[i] > lmax)
  45                                 break;
  46                         i++;
  47                 }
  48                 dir = 0;
  49         } else {
  50                 while(i < GraphTraceLen) {
  51                         if( !(dest[i] < dest[i-1]) && dest[i] < lmin)
  52                                 break;
  53                         i++;
  54                 }
  55                 dir = 1;
  56         }
  57
  58         lastval = i++;
  59         half_switch = 0;
  60         pmc = 0;
  61         block_done = 0;
  62
  63         for (bitidx = 0; i < GraphTraceLen; i++) {
  64                 if ((dest[i-1] > dest[i] && dir == 1 && dest[i] > lmax) || (dest[i-1] < dest[i] && dir == 0 && dest[i] < lmin)) {
  65                         lc = i - lastval;
  66                         lastval = i;
  67
  68                         // Switch depending on lc length:
  69                         // Tolerance is 1/8 of clock rate (arbitrary)
  70                         if (ABS(lc-clock/4) < tolerance) {
  71                                 // 16T0
  72                                 if((i - pmc) == lc) { /* 16T0 was previous one */
  73                                         /* It's a PMC ! */
  74                                         i += (128+127+16+32+33+16)-1;
  75                                         lastval = i;
  76                                         pmc = 0;
  77                                         block_done = 1;
  78                                 } else {
  79                                         pmc = i;
  80                                 }
  81                         } else if (ABS(lc-clock/2) < tolerance) {
  82                                 // 32TO
  83                                 if((i - pmc) == lc) { /* 16T0 was previous one */
  84                                         /* It's a PMC ! */
  85                                         i += (128+127+16+32+33)-1;
  86                                         lastval = i;
  87                                         pmc = 0;
  88                                         block_done = 1;
  89                                 } else if(half_switch == 1) {
  90                                         bits[bitidx++] = 0;
  91                                         half_switch = 0;
  92                                 }
  93                                 else
  94                                         half_switch++;
  95                         } else if (ABS(lc-clock) < tolerance) {
  96                                 // 64TO
  97                                 bits[bitidx++] = 1;
  98                         } else {
  99                                 // Error
 100                                 if (++warnings > 10) {
 101                                         Dbprintf("Error: too many detection errors, aborting.");
 102                                         return 0;
 103                                 }
 104                         }
 105
 106                         if(block_done == 1) {
 107                                 if(bitidx == 128) {
 108                                         for(j = 0; j < 16; ++j) {
 109                                                 blocks[num_blocks][j] =
 110                                                         128 * bits[j*8 + 7]+
 111                                                                                         64 * bits[j*8 + 6] +
 112                                                         32 * bits[j*8 + 5] +
 113                                                         16 * bits[j*8 + 4] +
 114                                                         8 * bits[j*8 + 3] +
 115                                                         4 * bits[j*8 + 2] +
 116                                                         2 * bits[j*8 + 1] +
 117                                                         bits[j*8]
 118                                                 ;
 119                                         }
 120                                         num_blocks++;
 121                                 }
 122                                 bitidx = 0;
 123                                 block_done = 0;
 124                                 half_switch = 0;
 125                         }
 126                         if(i < GraphTraceLen)
 127                                 dir = (dest[i-1] > dest[i]) ? 0 : 1;
 128                 }
 129                 if(bitidx==255)
 130                         bitidx=0;
 131                 warnings = 0;
 132                 if(num_blocks == 4) break;
 133         }
 134         memcpy(outBlocks, blocks, 16 * num_blocks);
 135         return num_blocks;
 136 }
 137
 138 bool IsBlock0PCF7931(uint8_t *block) {
 139         // assuming all RFU bits are set to 0
 140         // if PAC is enabled password is set to 0
 141         if (block[7] == 0x01)
 142         {
 143                 if (!memcmp(block, "\x00\x00\x00\x00\x00\x00\x00", 7) && !memcmp(block+9, "\x00\x00\x00\x00\x00\x00\x00", 7))
 144                         return true;
 145         }
 146         else if (block[7] == 0x00)
 147         {
 148                 if (!memcmp(block+9, "\x00\x00\x00\x00\x00\x00\x00", 7))
 149                         return true;
 150         }
 151         return false;
 152 }
 153
 154 bool IsBlock1PCF7931(uint8_t *block) {
 155         // assuming all RFU bits are set to 0
 156
 157         uint8_t rb1 = block[14] & 0x80;
 158         uint8_t rfb = block[14] & 0x7f;
 159         uint8_t rlb = block[15];
 160
 161         if (block[10] == 0 && block[11] == 0 && block[12] == 0 && block[13] == 0)
 162                 // block 1 is sent only if (RLB >= 1 && RFB <= 1) or RB1 enabled
 163                 if(rfb <= rlb && rfb <= 9 && rlb <= 9 && ((rfb <= 1 && rlb >= 1) || rb1))
 164                         return true;
 165
 166         return false;
 167 }
 168
 169 void ReadPCF7931() {
 170         int found_blocks = 0; // successfully read blocks
 171         int max_blocks = 8; // readable blocks
 172         uint8_t memory_blocks[8][17]; // PCF content
 173
 174         uint8_t single_blocks[8][17]; // PFC blocks with unknown position
 175         int single_blocks_cnt = 0;
 176
 177         size_t n = 0; // transmitted blocks
 178         uint8_t tmp_blocks[4][16]; // temporary read buffer
 179
 180         uint8_t found_0_1 = 0; // flag: blocks 0 and 1 were found
 181         int errors = 0; // error counter
 182         int tries = 0; // tries counter
 183
 184         memset(memory_blocks, 0, 8*17*sizeof(uint8_t));
 185         memset(single_blocks, 0, 8*17*sizeof(uint8_t));
 186
 187         int i = 0, j = 0;
 188
 189         do {
 190                 i = 0;
 191
 192                 memset(tmp_blocks, 0, 4*16*sizeof(uint8_t));
 193                 n = DemodPCF7931((uint8_t**)tmp_blocks);
 194                 if(!n)
 195                         ++errors;
 196
 197                 // exit if no block is received
 198                 if (errors >= 10 && found_blocks == 0 && single_blocks_cnt == 0) {
 199                         Dbprintf("Error, no tag or bad tag");
 200                         return;
 201                 }
 202
 203                 // exit if too many errors during reading
 204                 if (tries > 50 && (2*errors > tries)) {
 205                         Dbprintf("Error reading the tag");
 206                         Dbprintf("Here is the partial content");
 207                         goto end;
 208                 }
 209
 210                 // our logic breaks if we don't get at least two blocks
 211                 if (n < 2) {
 212                         // skip if all 0s block or no blocks
 213                         if (n == 0 || !memcmp(tmp_blocks[0], "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16))
 214                                 continue;
 215
 216                         // add block to single blocks list
 217                         if (single_blocks_cnt < max_blocks) {
 218                                 for (i = 0; i < single_blocks_cnt; ++i) {
 219                                         if (!memcmp(single_blocks[i], tmp_blocks[0], 16)) {
 220                                                 j = 1;
 221                                                 break;
 222                                         }
 223                                 }
 224                                 if (j != 1) {
 225                                         memcpy(single_blocks[single_blocks_cnt], tmp_blocks[0], 16);
 226                                         print_result("got single block", single_blocks[single_blocks_cnt], 16);
 227                                         single_blocks_cnt++;
 228                                 }
 229                                 j = 0;
 230                         }
 231                         ++tries;
 232                         continue;
 233                 }
 234
 235                 Dbprintf("(dbg) got %d blocks (%d/%d found) (%d tries, %d errors)", n, found_blocks, (max_blocks == 0 ? found_blocks : max_blocks), tries, errors);
 236                 for (i = 0; i < n; ++i)
 237                 {
 238                         print_result("got consecutive blocks", tmp_blocks[i], 16);
 239                 }
 240
 241                 i = 0;
 242                 if(!found_0_1) {
 243                         while (i < n - 1) {
 244                                 if (IsBlock0PCF7931(tmp_blocks[i]) && IsBlock1PCF7931(tmp_blocks[i+1])) {
 245                                         found_0_1 = 1;
 246                                         memcpy(memory_blocks[0], tmp_blocks[i], 16);
 247                                         memcpy(memory_blocks[1], tmp_blocks[i+1], 16);
 248                                         memory_blocks[0][ALLOC] = memory_blocks[1][ALLOC] = 1;
 249                                         // block 1 tells how many blocks are going to be sent
 250                                         max_blocks = MAX((memory_blocks[1][14] & 0x7f), memory_blocks[1][15]) + 1;
 251                                         found_blocks = 2;
 252
 253                                         Dbprintf("Found blocks 0 and 1. PCF is transmitting %d blocks.", max_blocks);
 254
 255                                         // handle the following blocks
 256                                         for (j = i + 2; j < n; ++j) {
 257                                                 memcpy(memory_blocks[found_blocks], tmp_blocks[j], 16);
 258                                                 memory_blocks[found_blocks][ALLOC] = 1;
 259                                                 ++found_blocks;
 260                                         }
 261                                         break;
 262                                 }
 263                                 ++i;
 264                         }
 265                 } else {
 266                         // Trying to re-order blocks
 267                         // Look for identical block in memory blocks
 268                         while (i < n-1) {
 269                                 // skip all zeroes blocks
 270                                 if (memcmp(tmp_blocks[i], "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16)) {
 271                                         for (j = 1; j < max_blocks - 1; ++j) {
 272                                                 if (!memcmp(tmp_blocks[i], memory_blocks[j], 16) && !memory_blocks[j+1][ALLOC]) {
 273                                                         memcpy(memory_blocks[j+1], tmp_blocks[i+1], 16);
 274                                                         memory_blocks[j+1][ALLOC] = 1;
 275                                                         if (++found_blocks >= max_blocks) goto end;
 276                                                 }
 277                                         }
 278                                 }
 279                                 if (memcmp(tmp_blocks[i+1], "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16)) {
 280                                         for (j = 0; j < max_blocks; ++j) {
 281                                                 if (!memcmp(tmp_blocks[i+1], memory_blocks[j], 16) && !memory_blocks[(j == 0 ? max_blocks : j) -1][ALLOC]) {
 282                                                         if (j == 0) {
 283                                                                 memcpy(memory_blocks[max_blocks - 1], tmp_blocks[i], 16);
 284                                                                 memory_blocks[max_blocks - 1][ALLOC] = 1;
 285                                                         } else {
 286                                                                 memcpy(memory_blocks[j-1], tmp_blocks[i], 16);
 287                                                                 memory_blocks[j-1][ALLOC] = 1;
 288                                                         }
 289                                                         if (++found_blocks >= max_blocks) goto end;
 290                                                 }
 291                                         }
 292                                 }
 293                                 ++i;
 294                         }
 295                 }
 296                 ++tries;
 297                 if (BUTTON_PRESS()) {
 298                         Dbprintf("Button pressed, stopping.");
 299                         goto end;
 300                 }
 301         }
 302         while (found_blocks < max_blocks);
 303
 304  end:
 305         Dbprintf("-----------------------------------------");
 306         Dbprintf("Memory content:");
 307         Dbprintf("-----------------------------------------");
 308         for (i = 0; i < max_blocks; ++i) {
 309                 if (memory_blocks[i][ALLOC])
 310                         print_result("Block", memory_blocks[i], 16);
 311                 else
 312                         Dbprintf("<missing block %d>", i);
 313         }
 314         Dbprintf("-----------------------------------------");
 315
 316         if (found_blocks < max_blocks) {
 317                 Dbprintf("-----------------------------------------");
 318                 Dbprintf("Blocks with unknown position:");
 319                 Dbprintf("-----------------------------------------");
 320                 for (i = 0; i < single_blocks_cnt; ++i)
 321                         print_result("Block", single_blocks[i], 16);
 322
 323                 Dbprintf("-----------------------------------------");
 324         }
 325         cmd_send(CMD_ACK,0,0,0,0,0);
 326 }
 327
 328 static void RealWritePCF7931(uint8_t *pass, uint16_t init_delay, int32_t l, int32_t p, uint8_t address, uint8_t byte, uint8_t data) {
 329         uint32_t tab[1024]={0}; // data times frame
 330         uint32_t u = 0;
 331         uint8_t parity = 0;
 332         bool comp = 0;
 333
 334         //BUILD OF THE DATA FRAME
 335         //alimentation of the tag (time for initializing)
 336         AddPatternPCF7931(init_delay, 0, 8192/2*T0_PCF, tab);
 337         AddPatternPCF7931(8192/2*T0_PCF + 319*T0_PCF+70, 3*T0_PCF, 29*T0_PCF, tab);
 338         //password indication bit
 339         AddBitPCF7931(1, tab, l, p);
 340         // password (on 56 bits)
 341         AddBytePCF7931(pass[0], tab, l, p);
 342         AddBytePCF7931(pass[1], tab, l, p);
 343         AddBytePCF7931(pass[2], tab, l, p);
 344         AddBytePCF7931(pass[3], tab, l, p);
 345         AddBytePCF7931(pass[4], tab, l, p);
 346         AddBytePCF7931(pass[5], tab, l, p);
 347         AddBytePCF7931(pass[6], tab, l, p);
 348         //programming mode (0 or 1)
 349         AddBitPCF7931(0, tab, l, p);
 350
 351         //block adress on 6 bits
 352         for (u = 0; u < 6; ++u) {
 353                 if (address & (1 << u)) {   // bit 1
 354                          ++parity;
 355                          AddBitPCF7931(1, tab, l, p);
 356                 } else {                    // bit 0
 357                          AddBitPCF7931(0, tab, l, p);
 358                 }
 359         }
 360
 361         //byte address on 4 bits
 362         for (u = 0; u < 4; ++u)
 363         {
 364                 if (byte & (1 << u)) {  // bit 1
 365                          parity++;
 366                          AddBitPCF7931(1, tab, l, p);
 367                 }
 368                 else                // bit 0
 369                          AddBitPCF7931(0, tab, l, p);
 370         }
 371
 372         //data on 8 bits
 373         for (u=0; u<8; u++)
 374         {
 375                 if (data&(1<<u)) {  // bit 1
 376                          parity++;
 377                          AddBitPCF7931(1, tab, l, p);
 378                 }
 379                 else                //bit 0
 380                          AddBitPCF7931(0, tab, l, p);
 381         }
 382
 383         //parity bit
 384         if ((parity % 2) == 0)
 385                 AddBitPCF7931(0, tab, l, p); //even parity
 386         else
 387                 AddBitPCF7931(1, tab, l, p);//odd parity
 388
 389         //time access memory
 390         AddPatternPCF7931(5120+2680, 0, 0, tab);
 391
 392         //conversion of the scale time
 393         for (u = 0; u < 500; ++u)
 394                 tab[u] = (tab[u] * 3) / 2;
 395
 396         //compennsation of the counter reload
 397         while (!comp) {
 398                 comp = 1;
 399                 for (u = 0; tab[u] != 0; ++u)
 400                         if(tab[u] > 0xFFFF) {
 401                           tab[u] -= 0xFFFF;
 402                           comp = 0;
 403                         }
 404         }
 405
 406         SendCmdPCF7931(tab);
 407 }
 408
 409 void BruteForcePCF7931(uint64_t password, uint8_t tries, uint16_t init_delay, int32_t l, int32_t p) {
 410         uint8_t i = 0;
 411         uint8_t pass_array[7];
 412
 413         while (password < 0x00FFFFFFFFFFFFFF) {
 414                 if (BUTTON_PRESS()) {
 415                         Dbprintf("Button pressed, stopping bruteforce ...");
 416                         return;
 417                 }
 418
 419                 num_to_bytes(password, 7, pass_array);
 420
 421                 Dbprintf("Trying: %02x %02x %02x %02x %02x %02x %02x ...",
 422                         pass_array[0],
 423                         pass_array[1],
 424                         pass_array[2],
 425                         pass_array[3],
 426                         pass_array[4],
 427                         pass_array[5],
 428                         pass_array[6]);
 429
 430                 for (i = 0; i < tries; ++i)
 431                         RealWritePCF7931
 432                         (
 433                                 pass_array,
 434                                 init_delay,
 435                                 l,
 436                                 p,
 437                                 0,
 438                                 7,
 439                                 0x01
 440                         );
 441
 442                 ++password;
 443         }
 444 }
 445
 446 /* Write on a byte of a PCF7931 tag
 447  * @param address : address of the block to write
 448    @param byte : address of the byte to write
 449         @param data : data to write
 450  */
 451 void WritePCF7931(uint8_t pass1, uint8_t pass2, uint8_t pass3, uint8_t pass4, uint8_t pass5, uint8_t pass6, uint8_t pass7, uint16_t init_delay, int32_t l, int32_t p, uint8_t address, uint8_t byte, uint8_t data) {
 452         Dbprintf("Initialization delay : %d us", init_delay);
 453         Dbprintf("Offsets : %d us on the low pulses width, %d us on the low pulses positions", l, p);
 454         Dbprintf("Password (LSB first on each byte): %02x %02x %02x %02x %02x %02x %02x", pass1, pass2, pass3, pass4, pass5, pass6, pass7);
 455         Dbprintf("Block address : %02x", address);
 456         Dbprintf("Byte address : %02x", byte);
 457         Dbprintf("Data : %02x", data);
 458
 459         uint8_t password[7] = {pass1, pass2, pass3, pass4, pass5, pass6, pass7};
 460
 461         RealWritePCF7931 (password, init_delay, l, p, address, byte, data);
 462 }
 463
 464
 465
 466 /* Send a trame to a PCF7931 tags
 467  * @param tab : array of the data frame
 468  */
 469
 470 void SendCmdPCF7931(uint32_t * tab) {
 471         uint16_t u=0;
 472         uint16_t tempo=0;
 473
 474         Dbprintf("Sending data frame ...");
 475
 476         FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
 477         FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
 478         FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_PASSTHRU );
 479
 480         LED_A_ON();
 481
 482         // steal this pin from the SSP and use it to control the modulation
 483         AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
 484         AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
 485
 486         //initialization of the timer
 487         AT91C_BASE_PMC->PMC_PCER |= (0x1 << 12) | (0x1 << 13) | (0x1 << 14);
 488         AT91C_BASE_TCB->TCB_BMR = AT91C_TCB_TC0XC0S_NONE | AT91C_TCB_TC1XC1S_TIOA0 | AT91C_TCB_TC2XC2S_NONE;
 489         AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS; // timer disable
 490         AT91C_BASE_TC0->TC_CMR = AT91C_TC_CLKS_TIMER_DIV3_CLOCK;  //clock at 48/32 MHz
 491         AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN;
 492         AT91C_BASE_TCB->TCB_BCR = 1;
 493
 494         tempo = AT91C_BASE_TC0->TC_CV;
 495         for (u = 0; tab[u] !=  0; u += 3) {
 496                 // modulate antenna
 497                 HIGH(GPIO_SSC_DOUT);
 498                 while(tempo !=  tab[u])
 499                         tempo = AT91C_BASE_TC0->TC_CV;
 500
 501                 // stop modulating antenna
 502                 LOW(GPIO_SSC_DOUT);
 503                 while(tempo !=  tab[u+1])
 504                         tempo = AT91C_BASE_TC0->TC_CV;
 505
 506                 // modulate antenna
 507                 HIGH(GPIO_SSC_DOUT);
 508                 while(tempo !=  tab[u+2])
 509                         tempo = AT91C_BASE_TC0->TC_CV;
 510         }
 511
 512         LED_A_OFF();
 513         FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 514         SpinDelay(200);
 515
 516         AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS; // timer disable
 517         DbpString("Data frame sent (multiple sends may be needed)");
 518         LED(0xFFFF, 1000);
 519 }
 520
 521
 522 /* Add a byte for building the data frame of PCF7931 tags
 523  * @param b : byte to add
 524  * @param tab : array of the data frame
 525  * @param l : offset on low pulse width
 526  * @param p : offset on low pulse positioning
 527  */
 528 bool AddBytePCF7931(uint8_t byte, uint32_t * tab, int32_t l, int32_t p) {
 529         uint32_t u;
 530         for (u = 0; u < 8; ++u) {
 531                 if (byte & (1 << u)) {  //bit is 1
 532                         if(AddBitPCF7931(1, tab, l, p)==1)return 1;
 533                 } else { //bit is 0
 534                         if(AddBitPCF7931(0, tab, l, p)==1)return 1;
 535                 }
 536         }
 537
 538         return 0;
 539 }
 540
 541 /* Add a bits for building the data frame of PCF7931 tags
 542  * @param b : bit to add
 543  * @param tab : array of the data frame
 544  * @param l : offset on low pulse width
 545  * @param p : offset on low pulse positioning
 546  */
 547 bool AddBitPCF7931(bool b, uint32_t * tab, int32_t l, int32_t p) {
 548         uint8_t u = 0;
 549
 550         for (u = 0; tab[u] != 0; u += 3){} //we put the cursor at the last value of the array
 551
 552         if (b == 1) {   //add a bit 1
 553                 if (u == 0) tab[u] = 34 * T0_PCF + p;
 554                 else        tab[u] = 34 * T0_PCF + tab[u-1] + p;
 555
 556                 tab[u+1] = 6 * T0_PCF+tab[u] + l;
 557                 tab[u+2] = 88 * T0_PCF+tab[u + 1] - l - p;
 558                 return 0;
 559         } else {        //add a bit 0
 560
 561                 if (u == 0) tab[u] = 98 * T0_PCF + p;
 562                 else        tab[u] = 98 * T0_PCF + tab[u-1] + p;
 563
 564                 tab[u + 1] = 6 * T0_PCF + tab[u] + l;
 565                 tab[u + 2] = 24 * T0_PCF + tab[u + 1] - l - p;
 566                 return 0;
 567         }
 568
 569         return 1;
 570 }
 571
 572 /* Add a custom pattern in the data frame
 573  * @param a : delay of the first high pulse
 574  * @param b : delay of the low pulse
 575  * @param c : delay of the last high pulse
 576  * @param tab : array of the data frame
 577  */
 578 bool AddPatternPCF7931(uint32_t a, uint32_t b, uint32_t c, uint32_t * tab) {
 579         uint32_t u = 0;
 580         for(u = 0; tab[u] != 0; u += 3){} //we put the cursor at the last value of the array
 581
 582         if (u == 0) tab[u] = a;
 583         else        tab[u] = a + tab[u - 1];
 584
 585         tab[u + 1] = b + tab[u];
 586         tab[u + 2] = c + tab[u + 1];
 587
 588         return 0;
 589 }