const PROGMEM uint32_t crc_table[256]={//
0, 1996959894,  3993919788, 2567524794, 124634137,  1886057615, 3915621685, 2657392035, 249268274,
2044508324, 3772115230, 2547177864, 162941995,  2125561021, 3887607047, 2428444049, 498536548,  
1789927666, 4089016648, 2227061214, 450548861,  1843258603, 4107580753, 2211677639, 325883990,  
1684777152, 4251122042, 2321926636, 335633487,  1661365465, 4195302755, 2366115317, 997073096,  
1281953886, 3579855332, 2724688242, 1006888145, 1258607687, 3524101629, 2768942443, 901097722,  
1119000684, 3686517206, 2898065728, 853044451,  1172266101, 3705015759, 2882616665, 651767980,  
1373503546, 3369554304, 3218104598, 565507253,  1454621731, 3485111705, 3099436303, 671266974,  
1594198024, 3322730930, 2970347812, 795835527,  1483230225, 3244367275, 3060149565, 1994146192, 
31158534, 2563907772, 4023717930, 1907459465, 112637215,  2680153253, 3904427059, 2013776290, 
251722036,  2517215374, 3775830040, 2137656763, 141376813,  2439277719, 3865271297, 1802195444, 
476864866,  2238001368, 4066508878, 1812370925, 453092731,  2181625025, 4111451223, 1706088902, 
314042704,  2344532202, 4240017532, 1658658271, 366619977,  2362670323, 4224994405, 1303535960, 
984961486,  2747007092, 3569037538, 1256170817, 1037604311, 2765210733, 3554079995, 1131014506, 
879679996,  2909243462, 3663771856, 1141124467, 855842277,  2852801631, 3708648649, 1342533948, 
654459306,  3188396048, 3373015174, 1466479909, 544179635,  3110523913, 3462522015, 1591671054, 
702138776,  2966460450, 3352799412, 1504918807, 783551873,  3082640443, 3233442989, 3988292384, 
2596254646, 62317068, 1957810842, 3939845945, 2647816111, 81470997, 1943803523, 3814918930, 
2489596804, 225274430,  2053790376, 3826175755, 2466906013, 167816743,  2097651377, 4027552580, 
2265490386, 503444072,  1762050814, 4150417245, 2154129355, 426522225,  1852507879, 4275313526, 
2312317920, 282753626,  1742555852, 4189708143, 2394877945, 397917763,  1622183637, 3604390888, 
2714866558, 953729732,  1340076626, 3518719985, 2797360999, 1068828381, 1219638859, 3624741850, 
2936675148, 906185462,  1090812512, 3747672003, 2825379669, 829329135,  1181335161, 3412177804, 
3160834842, 628085408,  1382605366, 3423369109, 3138078467, 570562233,  1426400815, 3317316542, 
2998733608, 733239954,  1555261956, 3268935591, 3050360625, 752459403,  1541320221, 2607071920, 
3965973030, 1969922972, 40735498, 2617837225, 3943577151, 1913087877, 83908371, 2512341634, 
3803740692, 2075208622, 213261112,  2463272603, 3855990285, 2094854071, 198958881,  2262029012, 
4057260610, 1759359992, 534414190,  2176718541, 4139329115, 1873836001, 414664567,  2282248934, 
4279200368, 1711684554, 285281116,  2405801727, 4167216745, 1634467795, 376229701,  2685067896, 
3608007406, 1308918612, 956543938,  2808555105, 3495958263, 1231636301, 1047427035, 2932959818, 
3654703836, 1088359270, 936918000,  2847714899, 3736837829, 1202900863, 817233897,  3183342108, 
3401237130, 1404277552, 615818150,  3134207493, 3453421203, 1423857449, 601450431,  3009837614, 
3294710456, 1567103746, 711928724,  3020668471, 3272380065, 1510334235, 755167117};

uint32_t Crc32(String buf)
{
  uint32_t crc;
  int len=buf.length();
  int index=0;
  crc = 0xFFFFFFFFUL;

  while (len--)
  {
    crc=pgm_read_dword_near(crc_table+((crc ^ buf[index]) & 0xFF))^(crc >> 8);
    index++;
  }
  return crc ^ 0xFFFFFFFFUL;
}