hash_fct_test.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
#include <gtest/gtest.h>
#include <hash-fct.H>
 
#include <cstring>
#include <random>
#include <set>
#include <string>
#include <vector>
 
using namespace Aleph;
 
// JSW hash requires initialization (defined in Aleph namespace in hash-fct.C)
namespace Aleph {
  extern void init_jsw() noexcept;
}
 
class HashTestEnvironment : public ::testing::Environment
{
public:
  void SetUp() override
  {
    init_jsw();
  }
};
 
// Register the environment to initialize jsw_hash table before any tests run
testing::Environment* const hash_env =
    testing::AddGlobalTestEnvironment(new HashTestEnvironment);
 
// ==================== Consistency Tests ====================
// Hash functions must produce the same output for the same input
 
class HashConsistencyTest : public ::testing::Test
{
protected:
  const char* test_string = "test_string_for_hashing";
  const std::string test_std_string = "test_string_for_hashing";
  const int test_int = 42;
  const double test_double = 3.14159265359;
};
 
TEST_F(HashConsistencyTest, AddHashConsistency)
{
  auto h1 = add_hash(test_string);
  auto h2 = add_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = add_hash(test_std_string);
  auto h4 = add_hash(test_std_string);
  EXPECT_EQ(h3, h4);
  EXPECT_EQ(h1, h3);  // const char* and std::string should match
 
  auto h5 = add_hash(test_int);
  auto h6 = add_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, XorHashConsistency)
{
  auto h1 = xor_hash(test_string);
  auto h2 = xor_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = xor_hash(test_std_string);
  auto h4 = xor_hash(test_std_string);
  EXPECT_EQ(h3, h4);
  EXPECT_EQ(h1, h3);
 
  auto h5 = xor_hash(test_int);
  auto h6 = xor_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, RotHashConsistency)
{
  auto h1 = rot_hash(test_string);
  auto h2 = rot_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = rot_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = rot_hash(test_int);
  auto h6 = rot_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, DjbHashConsistency)
{
  auto h1 = djb_hash(test_string);
  auto h2 = djb_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = djb_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = djb_hash(test_int);
  auto h6 = djb_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, SaxHashConsistency)
{
  auto h1 = sax_hash(test_string);
  auto h2 = sax_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = sax_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = sax_hash(test_int);
  auto h6 = sax_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, FnvHashConsistency)
{
  auto h1 = fnv_hash(test_string);
  auto h2 = fnv_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = fnv_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = fnv_hash(test_int);
  auto h6 = fnv_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, OatHashConsistency)
{
  auto h1 = oat_hash(test_string);
  auto h2 = oat_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = oat_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = oat_hash(test_int);
  auto h6 = oat_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, JswHashConsistency)
{
  auto h1 = jsw_hash(test_string);
  auto h2 = jsw_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = jsw_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = jsw_hash(test_int);
  auto h6 = jsw_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, ElfHashConsistency)
{
  auto h1 = elf_hash(test_string);
  auto h2 = elf_hash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = elf_hash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = elf_hash(test_int);
  auto h6 = elf_hash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, JenHashConsistency)
{
  unsigned seed = 12345;
  // Use std::string for consistency - const char* would use template version
  auto h1 = jen_hash(test_std_string, seed);
  auto h2 = jen_hash(test_std_string, seed);
  EXPECT_EQ(h1, h2);
 
  // Also test via void* API directly
  auto h3 = jen_hash((void*)test_string, strlen(test_string), seed);
  auto h4 = jen_hash((void*)test_std_string.c_str(), test_std_string.size(), seed);
  EXPECT_EQ(h3, h4);
 
  auto h5 = jen_hash(test_int, seed);
  auto h6 = jen_hash(test_int, seed);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, SuperFastHashConsistency)
{
  auto h1 = SuperFastHash(test_string);
  auto h2 = SuperFastHash(test_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = SuperFastHash(test_std_string);
  EXPECT_EQ(h1, h3);
 
  auto h5 = SuperFastHash(test_int);
  auto h6 = SuperFastHash(test_int);
  EXPECT_EQ(h5, h6);
}
 
TEST_F(HashConsistencyTest, Murmur3HashConsistency)
{
  unsigned long seed = 42;
  auto h1 = murmur3hash(test_std_string, seed);
  auto h2 = murmur3hash(test_std_string, seed);
  EXPECT_EQ(h1, h2);
 
  auto h3 = murmur3hash(test_int, seed);
  auto h4 = murmur3hash(test_int, seed);
  EXPECT_EQ(h3, h4);
}
 
TEST_F(HashConsistencyTest, DftHashFctConsistency)
{
  auto h1 = dft_hash_fct(test_std_string);
  auto h2 = dft_hash_fct(test_std_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = dft_hash_fct(test_int);
  auto h4 = dft_hash_fct(test_int);
  EXPECT_EQ(h3, h4);
}
 
// ==================== Edge Case Tests ====================
 
class HashEdgeCaseTest : public ::testing::Test
{
protected:
  const char* empty_string = "";
  const std::string empty_std_string = "";
  const char* single_char = "a";
  std::string large_string;
 
  void SetUp() override
  {
    // Create a large string (1MB)
    large_string.resize(1024 * 1024, 'x');
  }
};
 
TEST_F(HashEdgeCaseTest, EmptyStringHash)
{
  // Empty strings should hash consistently (though maybe to 0 for simple hashes)
  EXPECT_EQ(add_hash(empty_string), add_hash(empty_std_string));
  EXPECT_EQ(xor_hash(empty_string), xor_hash(empty_std_string));
  EXPECT_EQ(rot_hash(empty_string), rot_hash(empty_std_string));
  EXPECT_EQ(djb_hash(empty_string), djb_hash(empty_std_string));
  EXPECT_EQ(sax_hash(empty_string), sax_hash(empty_std_string));
  EXPECT_EQ(fnv_hash(empty_string), fnv_hash(empty_std_string));
  EXPECT_EQ(oat_hash(empty_string), oat_hash(empty_std_string));
  EXPECT_EQ(jsw_hash(empty_string), jsw_hash(empty_std_string));
  EXPECT_EQ(elf_hash(empty_string), elf_hash(empty_std_string));
  EXPECT_EQ(SuperFastHash(empty_string), SuperFastHash(empty_std_string));
}
 
TEST_F(HashEdgeCaseTest, SingleCharHash)
{
  const std::string single_std = "a";
 
  // All hashes should produce non-zero for single char 'a'
  EXPECT_NE(add_hash(single_char), 0u);
  EXPECT_NE(xor_hash(single_char), 0u);
  EXPECT_NE(rot_hash(single_char), 0u);
  EXPECT_NE(djb_hash(single_char), 0u);
  EXPECT_NE(sax_hash(single_char), 0u);
  EXPECT_NE(fnv_hash(single_char), 0u);
  EXPECT_NE(oat_hash(single_char), 0u);
  EXPECT_NE(jsw_hash(single_char), 0u);
  EXPECT_NE(elf_hash(single_char), 0u);
  EXPECT_NE(SuperFastHash(single_char), 0u);
 
  // Verify consistency
  EXPECT_EQ(add_hash(single_char), add_hash(single_std));
}
 
TEST_F(HashEdgeCaseTest, LargeStringHash)
{
  // Large strings should hash correctly
  auto h1 = fnv_hash(large_string);
  auto h2 = fnv_hash(large_string);
  EXPECT_EQ(h1, h2);
 
  auto h3 = SuperFastHash(large_string);
  auto h4 = SuperFastHash(large_string);
  EXPECT_EQ(h3, h4);
 
  auto h5 = oat_hash(large_string);
  auto h6 = oat_hash(large_string);
  EXPECT_EQ(h5, h6);
 
  auto h7 = murmur3hash(large_string, 42ul);
  auto h8 = murmur3hash(large_string, 42ul);
  EXPECT_EQ(h7, h8);
}
 
TEST_F(HashEdgeCaseTest, BinaryDataWithNulls)
{
  // Test hashing data with embedded null bytes
  char data1[] = {1, 0, 2, 0, 3};
  char data2[] = {1, 0, 2, 0, 3};
 
  EXPECT_EQ(add_hash(data1, 5), add_hash(data2, 5));
  EXPECT_EQ(fnv_hash(data1, 5), fnv_hash(data2, 5));
  EXPECT_EQ(oat_hash(data1, 5), oat_hash(data2, 5));
  EXPECT_EQ(SuperFastHash(data1, 5), SuperFastHash(data2, 5));
  EXPECT_EQ(jen_hash(data1, 5), jen_hash(data2, 5));
}
 
// ==================== Different Inputs Produce Different Hashes ====================
 
class HashDifferenceTest : public ::testing::Test
{
};
 
TEST_F(HashDifferenceTest, DifferentStringsDifferentHashes)
{
  const char* s1 = "hello";
  const char* s2 = "world";
  const char* s3 = "hello1";  // Very similar to s1
 
  // Production-quality hashes should distinguish these
  EXPECT_NE(fnv_hash(s1), fnv_hash(s2));
  EXPECT_NE(fnv_hash(s1), fnv_hash(s3));
 
  EXPECT_NE(oat_hash(s1), oat_hash(s2));
  EXPECT_NE(oat_hash(s1), oat_hash(s3));
 
  EXPECT_NE(SuperFastHash(s1), SuperFastHash(s2));
  EXPECT_NE(SuperFastHash(s1), SuperFastHash(s3));
 
  EXPECT_NE(djb_hash(s1), djb_hash(s2));
  EXPECT_NE(sax_hash(s1), sax_hash(s2));
  EXPECT_NE(elf_hash(s1), elf_hash(s2));
  EXPECT_NE(jsw_hash(s1), jsw_hash(s2));
}
 
TEST_F(HashDifferenceTest, DifferentIntsDifferentHashes)
{
  int i1 = 1;
  int i2 = 2;
  int i3 = 1000000;
 
  EXPECT_NE(fnv_hash(i1), fnv_hash(i2));
  EXPECT_NE(fnv_hash(i1), fnv_hash(i3));
 
  EXPECT_NE(oat_hash(i1), oat_hash(i2));
  EXPECT_NE(SuperFastHash(i1), SuperFastHash(i2));
  EXPECT_NE(djb_hash(i1), djb_hash(i2));
}
 
TEST_F(HashDifferenceTest, DifferentSeedsDifferentHashes)
{
  const std::string key = "test_key";
 
  auto h1 = jen_hash(key, 1);
  auto h2 = jen_hash(key, 2);
  auto h3 = jen_hash(key, 100);
 
  EXPECT_NE(h1, h2);
  EXPECT_NE(h1, h3);
  EXPECT_NE(h2, h3);
 
  auto m1 = murmur3hash(key, 1ul);
  auto m2 = murmur3hash(key, 2ul);
  auto m3 = murmur3hash(key, 100ul);
 
  EXPECT_NE(m1, m2);
  EXPECT_NE(m1, m3);
  EXPECT_NE(m2, m3);
}
 
// ==================== Void Pointer API Tests ====================
 
class HashVoidPtrTest : public ::testing::Test
{
};
 
TEST_F(HashVoidPtrTest, IntArrayHash)
{
  int arr1[] = {1, 2, 3, 4, 5};
  int arr2[] = {1, 2, 3, 4, 5};
  int arr3[] = {1, 2, 3, 4, 6};  // Different
 
  EXPECT_EQ(add_hash(arr1, sizeof(arr1)), add_hash(arr2, sizeof(arr2)));
  EXPECT_NE(add_hash(arr1, sizeof(arr1)), add_hash(arr3, sizeof(arr3)));
 
  EXPECT_EQ(fnv_hash(arr1, sizeof(arr1)), fnv_hash(arr2, sizeof(arr2)));
  EXPECT_NE(fnv_hash(arr1, sizeof(arr1)), fnv_hash(arr3, sizeof(arr3)));
 
  EXPECT_EQ(oat_hash(arr1, sizeof(arr1)), oat_hash(arr2, sizeof(arr2)));
  EXPECT_EQ(SuperFastHash(arr1, sizeof(arr1)), SuperFastHash(arr2, sizeof(arr2)));
  // jen_hash with void* requires explicit cast for arrays and explicit initval to avoid ambiguity with template overload
  EXPECT_EQ(jen_hash((void*)arr1, sizeof(arr1), Default_Hash_Seed), jen_hash((void*)arr2, sizeof(arr2), Default_Hash_Seed));
}
 
TEST_F(HashVoidPtrTest, StructHash)
{
  // Use a packed struct or memset to ensure no padding issues
  struct TestStruct
  {
    int a;
    double b;
    char c;
  };
 
  // Zero-initialize to avoid uninitialized padding bytes
  TestStruct s1, s2, s3;
  memset(&s1, 0, sizeof(s1));
  memset(&s2, 0, sizeof(s2));
  memset(&s3, 0, sizeof(s3));
  s1.a = 1; s1.b = 2.5; s1.c = 'x';
  s2.a = 1; s2.b = 2.5; s2.c = 'x';
  s3.a = 1; s3.b = 2.5; s3.c = 'y';
 
  EXPECT_EQ(fnv_hash(&s1, sizeof(s1)), fnv_hash(&s2, sizeof(s2)));
  EXPECT_NE(fnv_hash(&s1, sizeof(s1)), fnv_hash(&s3, sizeof(s3)));
 
  EXPECT_EQ(oat_hash(&s1, sizeof(s1)), oat_hash(&s2, sizeof(s2)));
  EXPECT_EQ(SuperFastHash(&s1, sizeof(s1)), SuperFastHash(&s2, sizeof(s2)));
}
 
// ==================== Template API Tests ====================
 
class HashTemplateTest : public ::testing::Test
{
};
 
TEST_F(HashTemplateTest, IntTemplateHash)
{
  int val = 12345;
 
  // Template versions should work
  auto h1 = add_hash(val);
  auto h2 = add_hash(&val, sizeof(val));
  EXPECT_EQ(h1, h2);
 
  auto h3 = fnv_hash(val);
  auto h4 = fnv_hash(&val, sizeof(val));
  EXPECT_EQ(h3, h4);
}
 
TEST_F(HashTemplateTest, DoubleTemplateHash)
{
  double val = 3.14159;
 
  auto h1 = fnv_hash(val);
  auto h2 = fnv_hash(&val, sizeof(val));
  EXPECT_EQ(h1, h2);
 
  auto h3 = oat_hash(val);
  auto h4 = oat_hash(&val, sizeof(val));
  EXPECT_EQ(h3, h4);
}
 
TEST_F(HashTemplateTest, LongLongTemplateHash)
{
  long long val = 9223372036854775807LL;
 
  auto h1 = fnv_hash(val);
  auto h2 = fnv_hash(&val, sizeof(val));
  EXPECT_EQ(h1, h2);
 
  auto h3 = SuperFastHash(val);
  auto h4 = SuperFastHash(&val, sizeof(val));
  EXPECT_EQ(h3, h4);
}
 
// ==================== Pair Hash Functions ====================
 
TEST(PairHashTest, PairDftHashFct)
{
  std::pair<int, int> p1{1, 2};
  std::pair<int, int> p2{1, 2};
  std::pair<int, int> p3{2, 1};
 
  auto h1 = pair_dft_hash_fct(p1);
  auto h2 = pair_dft_hash_fct(p2);
  auto h3 = pair_dft_hash_fct(p3);
 
  EXPECT_EQ(h1, h2);
  // Note: pair_dft_hash_fct uses addition, so {1,2} and {2,1} might collide
  // This is a known limitation of simple combination functions
  (void)h3;  // Suppress unused variable warning - see comment above
}
 
TEST(PairHashTest, PairSndHashFct)
{
  std::pair<std::string, std::string> p1{"hello", "world"};
  std::pair<std::string, std::string> p2{"hello", "world"};
 
  auto h1 = pair_snd_hash_fct(p1);
  auto h2 = pair_snd_hash_fct(p2);
 
  EXPECT_EQ(h1, h2);
}
 
// ==================== Distribution Quality Tests ====================
 
class HashDistributionTest : public ::testing::Test
{
protected:
  static constexpr size_t NUM_KEYS = 10000;
  std::vector<std::string> keys;
 
  void SetUp() override
  {
    std::mt19937 gen(42);  // Fixed seed for reproducibility
    std::uniform_int_distribution<> len_dist(5, 20);
    std::uniform_int_distribution<> char_dist('a', 'z');
 
    for (size_t i = 0; i < NUM_KEYS; ++i)
      {
        int len = len_dist(gen);
        std::string s;
        s.reserve(len);
        for (int j = 0; j < len; ++j)
          s += static_cast<char>(char_dist(gen));
        keys.push_back(std::move(s));
      }
  }
 
  // Measure hash uniqueness (collision ratio without modulo)
  // Good hash functions should have very few or no collisions
  double measureHashUniqueness(const std::vector<size_t>& hashes)
  {
    std::set<size_t> unique_hashes(hashes.begin(), hashes.end());
    return static_cast<double>(unique_hashes.size()) /
           static_cast<double>(hashes.size());
  }
};
 
// Test that production-quality hash functions produce mostly unique hashes
// (without modulo). We expect >90% uniqueness for 10000 distinct random strings.
TEST_F(HashDistributionTest, FnvHashUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(fnv_hash(key));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "FNV hash uniqueness: " << uniqueness;
}
 
TEST_F(HashDistributionTest, OatHashUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(oat_hash(key));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "OAT hash uniqueness: " << uniqueness;
}
 
TEST_F(HashDistributionTest, SuperFastHashUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(SuperFastHash(key));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "SuperFastHash uniqueness: " << uniqueness;
}
 
TEST_F(HashDistributionTest, JenHashUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(jen_hash(key, 0));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "Jenkins hash uniqueness: " << uniqueness;
}
 
TEST_F(HashDistributionTest, Murmur3HashUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(murmur3hash(key, 42ul));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "MurmurHash3 uniqueness: " << uniqueness;
}
 
TEST_F(HashDistributionTest, DftHashFctUniqueness)
{
  std::vector<size_t> hashes;
  hashes.reserve(NUM_KEYS);
  for (const auto& key : keys)
    hashes.push_back(dft_hash_fct(key));
 
  double uniqueness = measureHashUniqueness(hashes);
  EXPECT_GT(uniqueness, 0.90) << "dft_hash_fct uniqueness: " << uniqueness;
}
 
// ==================== Avalanche Property Tests ====================
// Small changes in input should cause large changes in output
 
class HashAvalancheTest : public ::testing::Test
{
protected:
  // Count bit differences between two hash values
  static int bitDifference(size_t h1, size_t h2)
  {
    size_t diff = h1 ^ h2;
    int count = 0;
    while (diff)
      {
        count += diff & 1;
        diff >>= 1;
      }
    return count;
  }
};
 
TEST_F(HashAvalancheTest, SingleBitChangeJenkins)
{
  // Changing a single bit should cause ~50% of output bits to change
  // for a good hash function
  unsigned char data1[16] = {0};
  unsigned char data2[16] = {0};
  data2[0] = 1;  // Single bit difference
 
  auto h1 = jen_hash(data1, 16);
  auto h2 = jen_hash(data2, 16);
 
  int bit_diff = bitDifference(h1, h2);
  // Good hash should have at least 20% of bits different
  EXPECT_GT(bit_diff, (int)(sizeof(size_t) * 8 * 0.2))
      << "Jenkins hash has poor avalanche property";
}
 
TEST_F(HashAvalancheTest, SingleBitChangeMurmur3)
{
  unsigned char data1[16] = {0};
  unsigned char data2[16] = {0};
  data2[0] = 1;
 
  auto h1 = murmur3hash(std::string((char*)data1, 16), 42ul);
  auto h2 = murmur3hash(std::string((char*)data2, 16), 42ul);
 
  int bit_diff = bitDifference(h1, h2);
  EXPECT_GT(bit_diff, (int)(sizeof(size_t) * 8 * 0.2))
      << "MurmurHash3 has poor avalanche property";
}
 
TEST_F(HashAvalancheTest, SingleBitChangeOat)
{
  unsigned char data1[16] = {0};
  unsigned char data2[16] = {0};
  data2[0] = 1;
 
  auto h1 = oat_hash(data1, 16);
  auto h2 = oat_hash(data2, 16);
 
  int bit_diff = bitDifference(h1, h2);
  EXPECT_GT(bit_diff, (int)(sizeof(size_t) * 8 * 0.2))
      << "One-at-a-Time hash has poor avalanche property";
}
 
// ==================== Known Value Tests ====================
// Test against known hash values for regression testing
 
TEST(HashKnownValuesTest, AddHashKnownValue)
{
  // "abc" = 97 + 98 + 99 = 294
  EXPECT_EQ(add_hash("abc"), 294u);
}
 
TEST(HashKnownValuesTest, XorHashKnownValue)
{
  // "abc" = 97 ^ 98 ^ 99 = 96
  EXPECT_EQ(xor_hash("abc"), 96u);
}
 
TEST(HashKnownValuesTest, FnvHashStartValue)
{
  // Empty string with fnv_hash should return the FNV offset basis
  // Since our implementation iterates while (*p), empty string returns
  // initial value
  EXPECT_EQ(fnv_hash(""), 2166136261u);
}
 
// ==================== Seeded Hash Tests ====================
 
TEST(SeededHashTest, JenHashWithDefaultSeed)
{
  const std::string data = "test";
  auto h1 = jen_hash(data, Default_Hash_Seed);
  auto h2 = jen_hash((void*)data.c_str(), data.size(), Default_Hash_Seed);
  EXPECT_EQ(h1, h2);
}
 
TEST(SeededHashTest, DftHashFctWithSeed)
{
  const std::string key = "test_key";
 
  auto h1 = dft_hash_fct(key, 1ul);
  auto h2 = dft_hash_fct(key, 2ul);
 
  EXPECT_NE(h1, h2);  // Different seeds should produce different hashes
}
 
// ==================== Type Safety Tests ====================
 
TEST(HashTypeSafetyTest, SignedUnsignedConsistency)
{
  int signed_val = -1;
  unsigned int unsigned_val = static_cast<unsigned int>(-1);
 
  // These should hash the same as they have the same bit representation
  auto h1 = fnv_hash(&signed_val, sizeof(signed_val));
  auto h2 = fnv_hash(&unsigned_val, sizeof(unsigned_val));
  EXPECT_EQ(h1, h2);
}
 
TEST(HashTypeSafetyTest, ConstCharPtrAndStringConsistency)
{
  // Test that const char* and std::string versions produce same hashes
  // Note: char arr[] uses template version which includes null terminator,
  // so we test const char* and std::string which both hash the string content
  const char* ptr = "hello";
  std::string str = "hello";
 
  EXPECT_EQ(fnv_hash(ptr), fnv_hash(str));
  EXPECT_EQ(oat_hash(ptr), oat_hash(str));
  EXPECT_EQ(djb_hash(ptr), djb_hash(str));
  EXPECT_EQ(sax_hash(ptr), sax_hash(str));
  EXPECT_EQ(SuperFastHash(ptr), SuperFastHash(str));
}
 
// ==================== Performance Sanity Checks ====================
// These are not rigorous benchmarks but ensure hashes complete in
// reasonable time
 
TEST(HashPerformanceTest, LargeDataHashing)
{
  // 10MB of data
  std::string large_data(10 * 1024 * 1024, 'x');
 
  // These should complete without hanging
  auto h1 = fnv_hash(large_data);
  auto h2 = oat_hash(large_data);
  auto h3 = SuperFastHash(large_data);
  auto h4 = murmur3hash(large_data, 42ul);
 
  EXPECT_NE(h1, 0u);
  EXPECT_NE(h2, 0u);
  EXPECT_NE(h3, 0u);
  EXPECT_NE(h4, 0u);
}
 
TEST(HashPerformanceTest, ManySmallHashes)
{
  // Hash 100,000 small integers
  size_t sum = 0;
  for (int i = 0; i < 100000; ++i)
    sum += fnv_hash(i);
 
  EXPECT_NE(sum, 0u);
}