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  1. #include <cstring>
  2. #include <cassert>
  3. #include <cstdio>
  4.  
  5. #include <algorithm>
  6.  
  7. // Abstract
  8. // [!] In C++14 many of this funcs can be 'constexpr' [!]
  9. class MathUtils {
  10.  
  11. public:
  12.  
  13.   // 'hashSizeInBits' AND 'FNVPrime' should NOT be zero
  14.   //  (for FNV primes see here: http://i...content-available-to-author-only...e.com/chongo/tech/comp/fnv/)
  15.   // 'hashSizeInBits' should NOT be larger (OR even equal)
  16.   //  then size of 'unsigned long long int' in bits
  17.   // In the general case, almost any offset_basis will serve so long as it is non-zero
  18.   static unsigned long long int generateFNV1OffsetBasis(const size_t hashSizeInBits,
  19.                                                         const unsigned long long int FNVPrime) throw()
  20.   {
  21.     static const auto ULL_SIZE_IN_BITS = sizeof(unsigned long long int) * 8U;
  22.     static const char* const OFFSET_STR =
  23.       "chongo <Landon Curt Noll> /\\../\\!"; // http://w...content-available-to-author-only...e.com/chongo/odd/bat.html
  24.  
  25.     if (!hashSizeInBits || hashSizeInBits >= ULL_SIZE_IN_BITS || !FNVPrime) return 0ULL;
  26.  
  27.     const unsigned long long int hashMod =
  28.       static_cast<decltype(hashMod)>(std::pow(2.0, ULL_SIZE_IN_BITS));
  29.     auto offsetBasis = 0ULL;
  30.  
  31.     for (auto currChar = OFFSET_STR; *currChar; ++currChar) {
  32.       offsetBasis = (offsetBasis * FNVPrime) % hashMod;
  33.       offsetBasis ^= *currChar;
  34.     }
  35.     return offsetBasis;
  36.   }
  37.  
  38.   // 'str' SHOULD be a POD C null-terminated str.
  39.   // Returns zero for an empty str.
  40.   // FNV-1a algorithm description: http://i...content-available-to-author-only...e.com/chongo/tech/comp/fnv/#FNV-1a
  41.   static size_t getFNV1aHash(const char* str) throw() {
  42.     if (!str || !*str) return size_t();
  43.     static_assert(4U == sizeof(size_t) || 8U == sizeof(size_t),
  44.                   "Known primes & offsets for 32 OR 64 bit hashes ONLY");
  45.  
  46.     //// C++11 OPTIMIZATION HINT: better use 'constexpr' instead of 'const'
  47.  
  48.     // In the general case, almost any offset_basis will serve so long as it is non - zero
  49.     static const unsigned long long int BASISES[] =
  50.       {2166136261ULL, 14695981039346656037ULL}; // 32 bit, 64 bit
  51.     static const size_t OFFSET_BASIS =
  52.       static_cast<decltype(OFFSET_BASIS)>(BASISES[sizeof(size_t) / 4U - 1U]);
  53.  
  54.     // Some primes do hash better than other primes for a given integer size
  55.     static const unsigned long long int PRIMES[] =
  56.       {16777619ULL, 1099511628211ULL}; // 32 bit, 64 bit
  57.     static const size_t PRIME = 
  58.       static_cast<decltype(OFFSET_BASIS)>(PRIMES[sizeof(size_t) / 4U - 1U]);
  59.  
  60.     auto hash = OFFSET_BASIS;
  61.     do {
  62.       hash ^= *str++; // xor is performed on the low order octet (8 bits) of hash
  63.       hash *= PRIME;
  64.     } while (*str);
  65.  
  66.     return hash;
  67.   }
  68.  
  69. private:
  70.  
  71.   MathUtils() throw() = delete;
  72.   ~MathUtils() throw() = delete;
  73.   MathUtils(const MathUtils&) throw() = delete;
  74.   MathUtils(MathUtils&&) throw() = delete;
  75.   MathUtils& operator=(const MathUtils&) throw() = delete;
  76.   MathUtils& operator=(MathUtils&&) throw() = delete;
  77. };
  78.  
  79. #include <stdlib.h>
  80. #include <ctime>
  81. #include <cmath>
  82.  
  83. #include <time.h>
  84.  
  85. #include <string>
  86. #include <fstream>
  87. #include <iostream>
  88. #include <stdexcept>
  89. #include <unordered_map>
  90.  
  91. class HashTester {
  92.  
  93. public:
  94.  
  95.   typedef std::unordered_map<size_t, std::string> THashCodeToStrMap;
  96.  
  97.   static const auto MIN_CHAR_ = 'a';
  98.   static const auto MAX_CHAR_ = 'z'; // 'a'-'z': 26
  99.   static const auto ALPHABET_LEN_ = MAX_CHAR_ - MIN_CHAR_ + 1U;
  100.   static const char* const OUT_FILE_NAME_;
  101.   static const char* const OUT_FILE_NAME_EXT_;
  102.  
  103.   struct Stats {
  104.     Stats(const unsigned long long int comboCount = 0ULL) throw() : comboCount(comboCount) {}
  105.  
  106.     unsigned long long int totalCount = 0ULL, duplicateCount = 0ULL, comboCount;
  107.   };
  108.  
  109.   // Internal
  110.   template <const size_t BufCapacity>
  111.   struct Params {
  112.     Params(char (&strBuf)[BufCapacity], const size_t currLen = size_t(),
  113.            THashCodeToStrMap* const map = nullptr,
  114.            Stats* const stats = nullptr,
  115.            std::ofstream* const outFile = nullptr) throw()
  116.            : currLen(currLen), strBuf(strBuf), map(map), stats(stats), outFile(outFile)
  117.     {}
  118.  
  119.     size_t currLen = size_t();
  120.     char (&strBuf)[BufCapacity];
  121.     size_t lastCompletenessPercentage = size_t();
  122.  
  123.     THashCodeToStrMap* map = nullptr;
  124.     Stats* stats = nullptr;
  125.     std::ofstream* outFile = nullptr;
  126.   };
  127.  
  128.   // Char Sequence Generator Type
  129.   enum class ECCharSeqGenType {
  130.     CSGT_ALL_VARIANTS // a^N combinations (a - alphabet power; N - length of the seq., fixed)
  131.   };
  132.  
  133.   template <class THashFunctor, const size_t MaxStrLen = 4U>
  134.   static double getCollisionProbability(bool& error, const bool logCollisions = true) throw() {
  135.     char strBuf[MaxStrLen + 1U] = {0}; // even to 8: MaxStrLen + 8U - (MaxStrLen % 8U)
  136.     strBuf[std::extent<decltype(strBuf)>::value - 1U] = '\0';
  137.     static const auto COMBINATION_COUNT_ =
  138.       static_cast<unsigned long long int>(std::pow(ALPHABET_LEN_, MaxStrLen));
  139.  
  140.     THashCodeToStrMap map;
  141.     auto toReserveBucketCount
  142.       = static_cast<size_t>(COMBINATION_COUNT_ / static_cast<size_t>(std::pow(10.0, MaxStrLen / 2.0)));
  143.     while (true) {
  144.       try {
  145.         map.reserve(toReserveBucketCount);
  146.         break;
  147.       } catch (...) {
  148.         toReserveBucketCount /= 2U;
  149.       }
  150.     }
  151.     std::ofstream outFile;
  152.  
  153.     static const auto OUT_FILE_NAME_BUF_SIZE_ = 64U;
  154.     char outFileName[OUT_FILE_NAME_BUF_SIZE_] = {0};
  155.     if (logCollisions && !openFile(outFile, outFileName, sizeof(outFileName))) {
  156.       error = true;
  157.       return nan("");
  158.     }
  159.     Stats stats(COMBINATION_COUNT_);
  160.     Params<std::extent<decltype(strBuf)>::value> params(strBuf, 0U, &map, &stats, &outFile);
  161.  
  162.     if (params.stats->comboCount) std::cout << std::endl;
  163.     error = !createAndTestCharSeq<THashFunctor>(params, logCollisions); // returns false on ANY error
  164.     if (params.stats->comboCount) std::cout << std::endl;
  165.  
  166.     if (!params.stats->duplicateCount) { // NO duplicates - empty file
  167.       outFile.close(); // file will be auto flushed
  168.       const auto fileDeleteResult = remove(outFileName); // on failure, a nonzero value is returned
  169.     }
  170.     { // Shrink-to-fit
  171.       decltype(map) mapClearer(std::move(map)); // release mem. before flushing file
  172.     }
  173.     // File will be auto flushed AND closed here
  174.     return static_cast<double>(stats.duplicateCount) / stats.totalCount * 100.0;
  175.   }
  176.  
  177.   // Generic strategy to test auto. generated char. sequences
  178.   //  (used to test hashes, through can be useful elsewhere)
  179.   // [!] Will stop if mets zero hash. (AND return false) [!]
  180.   template <class TStrFunctor, const size_t BufCapacity>
  181.   static bool createAndTestCharSeq(Params<BufCapacity>& params, bool logCollisions = true) throw() {
  182.     static_assert(MIN_CHAR_ < MAX_CHAR_, "Invalid char. sequence");
  183.     static const auto LAST_CHAR_IDX_ = BufCapacity - 1U;
  184.  
  185.     logCollisions = logCollisions && params.outFile;
  186.  
  187.     const auto currIdx = params.currLen;
  188.     const auto nextIdx = currIdx + 1U;
  189.     const auto toReserveCount = nextIdx + 1U;
  190.     size_t currHash = 0U;
  191.     std::string currStr;
  192.     decltype(std::make_pair(currHash, std::move(currStr))) currPair;
  193.     decltype(params.map->insert(std::move(currPair))) insertResult;
  194.     TStrFunctor strFunctor;
  195.     auto completenessPercentage = 0U;
  196.  
  197.     auto tryInsert = [&]() throw() {
  198.       //// Fill pair
  199.       currStr.reserve(toReserveCount);
  200.       currStr = params.strBuf;
  201.       currHash = strFunctor(currStr);
  202.  
  203.       if (!params.map) return true; // skip other part
  204.       currPair.first = currHash;
  205.       if (logCollisions) currPair.second = currStr; // do NOT move, COPY
  206.  
  207.       try {
  208.         insertResult = params.map->insert(std::move(currPair));
  209.       } catch (...) {
  210.         return false;
  211.       };
  212.  
  213.       if (!insertResult.second) { // if NOT inserted (duplicate)
  214.         if (params.stats) ++params.stats->duplicateCount; // if collect stats
  215.  
  216.         if (logCollisions) {
  217.           auto& dupStr = (*insertResult.first).second;
  218.           (*params.outFile) << currHash << ": '" << currStr << "' == '" << dupStr << "'\n";
  219.           if (!(*params.outFile)) return false;
  220.         }
  221.       }
  222.       return true;
  223.     };
  224.  
  225.     static_assert(MIN_CHAR_ < MAX_CHAR_, "Invalid char codes");
  226.     for (char currChar = MIN_CHAR_; currChar <= MAX_CHAR_; ++currChar) {
  227.       params.strBuf[currIdx] = currChar;
  228.  
  229.       if (nextIdx < LAST_CHAR_IDX_) { // prolong seq.
  230.         params.currLen = nextIdx;
  231.         if (!createAndTestCharSeq<TStrFunctor, BufCapacity>(params, logCollisions)) return false;
  232.       } else { // seq. end
  233.         if (!tryInsert()) return false; // saving OR logging failed
  234.         if (!currHash) return false; // force stop (skip other) [OPTIMIZATION]
  235.  
  236.         if (params.stats) { // if collect stats
  237.           ++params.stats->totalCount;
  238.  
  239.           if (params.stats->comboCount) { // show progress
  240.             completenessPercentage
  241.               = static_cast<decltype(completenessPercentage)>(static_cast<double>(params.stats->totalCount)
  242.               / params.stats->comboCount * 100.0);
  243.  
  244.             if (completenessPercentage > params.lastCompletenessPercentage &&
  245.                 !(completenessPercentage % 10U))
  246.             { // step = 10U
  247.               std::cout << ' ' << completenessPercentage;
  248.               params.lastCompletenessPercentage = completenessPercentage;
  249.             }
  250.           }
  251.         }
  252.       }
  253.     } // 'for currChar' END
  254.     return true;
  255.   } // 'createAndTestCharSeqA' END
  256.  
  257. private:
  258.  
  259.   static bool openFile(std::ofstream& outFile, char* const fileNameBuf,
  260.                        const size_t fileNameBufSize) throw()
  261.   {
  262.     if (!fileNameBuf || fileNameBufSize < 2U) return false;
  263.     //// Create unique file name (ALSO clock ticks can be replaced with the time AND/OR random)
  264.     ////  i. e. C++11 'std::chrono' AND/OR 'std::uniform_int_distribution'
  265.     ////   ALSO C 'tmpnam' / 'tmpfile'
  266.     strncat(fileNameBuf, OUT_FILE_NAME_, fileNameBufSize - 1U);
  267.     static const auto STR_TIME_BUF_SIZE_ = 32U;
  268.     char strTimeBuf[STR_TIME_BUF_SIZE_] = {0};
  269.     // Better use C++11 http://e...content-available-to-author-only...e.com/w/cpp/chrono/high_resolution_clock
  270.     const auto nowTime = time(nullptr);
  271.     sprintf(strTimeBuf, "%lli", nowTime);
  272.     strncat(fileNameBuf, strTimeBuf, fileNameBufSize - 1U);
  273.     strncat(fileNameBuf, OUT_FILE_NAME_EXT_, fileNameBufSize - 1U);
  274.  
  275.     outFile.open(fileNameBuf, std::ios::out | std::ios::trunc);
  276.     return !(!outFile);
  277.   }
  278. };
  279.  
  280. const char* const HashTester::OUT_FILE_NAME_ = "collison_test_results#";
  281. const char* const HashTester::OUT_FILE_NAME_EXT_ = ".txt ";
  282.  
  283. // Functor
  284. #define ADD_HASHER_FOR(ClassName, HasherName) \
  285. template <typename T = ClassName>\
  286. struct HasherName {\
  287.   auto operator()(const T& obj) const throw() -> decltype(obj.hash()) {\
  288.     return obj.hash();\
  289.   }\
  290. };
  291.  
  292. // Functor
  293. #define ADD_STD_HASHER_FOR(ClassName) \
  294. namespace std {\
  295.   template <>\
  296.   class hash<ClassName> {\
  297.   public:\
  298.     size_t operator()(const ClassName& obj) const throw() {\
  299.       return obj.hash();\
  300.     }\
  301.   };\
  302. };
  303.  
  304. template <class TStrType>
  305. struct FNV1aHashFunctor {
  306.   auto operator()(const TStrType& str) throw() -> decltype(MathUtils::getFNV1aHash(str.c_str())) {
  307.     return MathUtils::getFNV1aHash(str.c_str());
  308.   }
  309. };
  310.  
  311. template <class TStrType>
  312. struct STLHashFunctor {
  313.   auto operator()(const TStrType& str) throw() -> decltype(std::hash<std::string>()(str)) {
  314.     return std::hash<std::string>()(str);
  315.   }
  316. };
  317.  
  318. int main() {
  319.   bool error = false;
  320.     const auto FNV1aHashCollisionProbability_
  321.       = HashTester::getCollisionProbability<FNV1aHashFunctor<std::string>>(error, false);
  322.     std::cout << std::endl << "FNV1a Collision Probability: "
  323.               << FNV1aHashCollisionProbability_ << ", error: " << error << std::endl;
  324.  
  325.     // 'std::hash<std::string>' can be used directly
  326.     error = false;
  327.     const auto STLHashCollisionProbability_
  328.       = HashTester::getCollisionProbability<STLHashFunctor<std::string>>(error, false);
  329.     std::cout << std::endl << "STL Collision Probability: "
  330.               << STLHashCollisionProbability_ << ", error: " << error << std::endl;
  331.   return 0;
  332. }
Success #stdin #stdout 0.63s 10616KB
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stdin
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Standard input is empty
stdout
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 10 20 30 40 50 60 70 80 90 100

FNV1a Collision Probability: 0, error: 0

 10 20 30 40 50 60 70 80 90 100

STL Collision Probability: 0, error: 0
https://ideone.com/6U6Ncs
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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