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

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