text: #include <stdint.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  #include <time.h>
  #include <math.h>
  #include <utility>
  #include <algorithm>
  #include <iostream>
  #include <cassert>
  #include <functional>
  
  using namespace std;
  
  // stochasticPerfectHash
  // orthopteroid@gmail.com
  // mixtable fixed at 64 slots, for efficiency
  
  // credit to http://web.mit.edu/freebsd/head/sys/libkern/crc32.c
  // credit to http://cs.mwsu.edu/~griffin/courses/2133/downloads/Spring11/p677-pearson.pdf
  
  struct KeyHash {
      uint8_t key;
      uint32_t hash;
  };
  
  //////////////////////
  
  // Uses codetable randomization to derive a Pearson mixing table for sets of alphabetic keys
  // although simple, requires contigious ascii chars for the keywords
  const char* validchars = "abcdefghijklmnopqrstuvwxyz";
  
  // given the string and the mix table, compute the pearson hash
  KeyHash ph_hash(const uint8_t *keyword, const uint8_t *mixTable, size_t pkSize)
  {
      uint8_t hash = mixTable[ keyword[0] - validchars[0] ]; // char 0
      for(uint i = 1; keyword[i]; i++) // chars 1 ... N
          hash = mixTable[ ( hash ^ ( keyword[i] - validchars[0] ) ) & 0b0111111 ];
      return {key: (uint8_t)(hash % pkSize), hash: hash };
  }
  
  //////////////////////
  
  // uses crc32 poly to calculate hash and subsequently derive a key from the 64 slot mixing table
  // no alphabetic restrictions on the keywords
  
  KeyHash crc32_hash(const uint8_t *keyword, const uint8_t *mixTable, size_t pkSize)
  {
      const uint32_t crc32_tab[] = {
              0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
              0xe963a535, 0x9e6495a3,	0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
              0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
              0xf3b97148, 0x84be41de,	0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
              0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,	0x14015c4f, 0x63066cd9,
              0xfa0f3d63, 0x8d080df5,	0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
              0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,	0x35b5a8fa, 0x42b2986c,
              0xdbbbc9d6, 0xacbcf940,	0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
              0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
              0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
              0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,	0x76dc4190, 0x01db7106,
              0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
              0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
              0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
              0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
              0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
              0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
              0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
              0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
              0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
              0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
              0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
              0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
              0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
              0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
              0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
              0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
              0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
              0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
              0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
              0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
              0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
              0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
              0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
              0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
              0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
              0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
              0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
              0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
              0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
              0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
              0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
              0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
      };
  
      const uint8_t *p = keyword;
      uint32_t crc = ~0U;
      while( *p ) crc = crc32_tab[(crc ^ *p++) & 0xFF] ^ (crc >> 8);
      crc = crc ^ ~0U;
  
      // now we hash the crc using the mixtable to (hopefully) derive a unique key
      auto key = ~0U;
      key ^= mixTable[(crc >> 26) & 0b0111111];
      key ^= mixTable[(crc >> 20) & 0b0111111];
      key ^= mixTable[(crc >> 14) & 0b0111111];
      key ^= mixTable[(crc >>  8) & 0b0111111];
      key ^= mixTable[(crc >>  2) & 0b0111111]; // leftovers
  
      return {key: (uint8_t)(key % pkSize), hash: crc };
  }
  
  ///////////////////////////
  
  // takes an array of keywords and returns permuted code and keywords tables that construct a perfect hash
  template<uint MaxIterations>
  bool sph_calc(uint &iter, const vector<string> &keywords, vector<uint8_t> &mixTable, vector<string> &permutedKeywords, vector<uint32_t> &hashes, std::function<KeyHash(const uint8_t*, const uint8_t*, size_t)> fn_hash)
  {
      vector<int> index(permutedKeywords.size());
  
      for(uint8_t c = 0; c < mixTable.size(); c++) { mixTable[ c ] = c +3; /* +3 to skip lower, less entropic values */ }
  
      // mixtable retry loop...
      uint iterations = 0;
      do {
          for(uint pk=0;pk<permutedKeywords.size();pk++) { index[pk] = -1; hashes[pk] = 0; }
  
          // trial hash all keywords. check for collisions
          uint k = 0;
          for( k = 0; k < keywords.size(); k++ )
          {
              auto kh = fn_hash((uint8_t*)keywords[k].data(), mixTable.data(), permutedKeywords.size());
              if( index[ kh.key ] != -1 ) break; // collision
              index[ kh.key ] = k;
              hashes[ kh.key ] = kh.hash;
          }
          if( k == keywords.size() ) { // no collisions
              for( uint pk = 0; pk < permutedKeywords.size(); pk++ )
                  if( index[ pk ] != -1 ) permutedKeywords[ pk ] = keywords[ index[ pk ] ];
  
              printf("Solution for %lu keywords using a %lu keyword table with a %lu slot mix table (%u iterations)\n", keywords.size(), permutedKeywords.size(), mixTable.size(), iterations);
  
              printf("uint8_t Mixtable[ %lu ] = { ", mixTable.size());
              for_each(mixTable.begin(), mixTable.end(), [] (const uint8_t c) { printf("%u, ", c); } );
              printf("};\n");
  
              printf("const char* Keyword[ %lu ] = { ", permutedKeywords.size());
              for_each(permutedKeywords.begin(), permutedKeywords.end(), [] (const string s) {
                  if(s.length() > 0)
                      printf("\"%s\", ", s.data());
                  else
                      printf("0, ");
              } );
              printf("};\n");
  
              printf("const uint32_t Hash[ %lu ] = { ", hashes.size());
              for_each(hashes.begin(), hashes.end(), [] (const uint32_t h) {
                  printf("0x%08X, ", h);
              } );
              printf("};\n");
  
              printf("enum Key { ");
              for( uint pk = 0; pk < permutedKeywords.size(); pk++ ) {
                  if(permutedKeywords[pk].length() == 0) continue;
                  auto kh = fn_hash((uint8_t*)permutedKeywords[pk].data(), mixTable.data(), permutedKeywords.size());
                  string identifier = permutedKeywords[pk];
                  for_each(identifier.begin(), identifier.end(), [](string::value_type& c ) { c = toupper(c); } );
                  printf("%s=%u, ", identifier.data(), kh.key);
                  assert(pk == kh.key);
              }
              printf("};\n");
  
              return false;
          }
  
          // permute the character mixtable
          for(uint i=0;i<mixTable.size()/2;i++) { std::swap(mixTable[i], mixTable[rand() % mixTable.size()]); }
  
          iter++;
      } while( ++iterations < MaxIterations );
  
      return true;
  }
  
  //////////////////////
  // demo code
  
  int main()
  {
      time_t ltime;
      time(&ltime);
      srand((unsigned int)ltime);
  
      const int keyCount = 10;
      const int maxIter = 500;
      const int trials = 3;
      vector<uint8_t> mixTable(64);
  
      for(uint t=0;t<trials;t++)
      {
          fflush(stdout);
  
          vector<string> keywords(keyCount);
  
          // init strings to random lowercase chars
          printf("Keywords (");
          for_each(keywords.begin(), keywords.end(), [&] (string &s) {
              int keyLength = 5 + rand() % 3;
              s.resize(keyLength);
              for(uint i=0;i<keyLength;i++) { s[ i ] = validchars[ rand() % strlen(validchars) ]; }
              cout << s << ", ";
          } );
          printf(")\n\n");
  
          {
              vector<string> permutedKeywords(keyCount);
              vector<uint32_t> hashes(keyCount);
              uint iterations = 0;
              bool collision = false;
              // try progressively larger keyword table
              for (uint i = keywords.size(); i < keywords.size() * 2; i++) {
                  permutedKeywords.resize(i);
                  hashes.resize(i);
                  collision = sph_calc<maxIter>(
                          iterations, keywords, mixTable, permutedKeywords, hashes,
                          ph_hash // with pearson hash
                  );
                  if (!collision) { break; }
              }
              printf("%s\n", collision ? "Failure!" : "");
          }
  
          {
              vector<string> permutedKeywords(keyCount);
              vector<uint32_t> hashes(keyCount);
              uint iterations = 0;
              bool collision = false;
              // try progressively larger keyword table
              for (uint i = keywords.size(); i < keywords.size() * 2; i++) {
                  permutedKeywords.resize(i);
                  hashes.resize(i);
                  collision = sph_calc<maxIter>(
                          iterations, keywords, mixTable, permutedKeywords, hashes,
                          crc32_hash // with crc32
                  );
                  if (!collision) { break; }
              }
              printf("%s\n", collision ? "Failure!" : "");
          }
      }
  
      return 0;
  }
  
  