PearsonHash

pearson.cpp

#include <cstdint>
#include <array>

uint64_t PearsonHash(const uint8_t *x, size_t len) 
{
  static const std::array<uint8_t, 256> T = {
    // 0-255 shuffled in any (random) order suffices
     98,  6, 85,150, 36, 23,112,164,135,207,169,  5, 26, 64,165,219,
     61, 20, 68, 89,130, 63, 52,102, 24,229,132,245, 80,216,195,115,
     90,168,156,203,177,120,  2,190,188,  7,100,185,174,243,162, 10,
    237, 18,253,225,  8,208,172,244,255,126,101, 79,145,235,228,121,
    123,251, 67,250,161,  0,107, 97,241,111,181, 82,249, 33, 69, 55,
     59,153, 29,  9,213,167, 84, 93, 30, 46, 94, 75,151,114, 73,222,
    197, 96,210, 45, 16,227,248,202, 51,152,252,125, 81,206,215,186,
     39,158,178,187,131,136,  1, 49, 50, 17,141, 91, 47,129, 60, 99,
    154, 35, 86,171,105, 34, 38,200,147, 58, 77,118,173,246, 76,254,
    133,232,196,144,198,124, 53,  4,108, 74,223,234,134,230,157,139,
    189,205,199,128,176, 19,211,236,127,192,231, 70,233, 88,146, 44,
    183,201, 22, 83, 13,214,116,109,159, 32, 95,226,140,220, 57, 12,
    221, 31,209,182,143, 92,149,184,148, 62,113, 65, 37, 27,106,166,
      3, 14,204, 72, 21, 41, 56, 66, 28,193, 40,217, 25, 54,179,117,
    238, 87,240,155,180,170,242,212,191,163, 78,218,137,194,175,110,
     43,119,224, 71,122,142, 42,160,104, 48,247,103, 15, 11,138,239 
  };
  uint64_t out = 0;
  for (size_t j = 0; j < sizeof(out); ++j) {
    uint8_t h = T[(x[0] + j) % 256];
    for (size_t i = 1; i < len; ++i)
       h = T[h ^ x[i]];
    out = (out << 8) | h;
  }
  return out;
}