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// Copyright (c) 2022 Johannes Stoelp
#include <types.h>
#include <utils.h>
#include <filesystem>
#include <fstream>
#include <gtest/gtest.h>
#include <iostream>
#include <vector>
using ID = std::array<u8, 6>;
namespace fs = std::filesystem;
std::vector<ID> read_blob() {
if (!fs::exists("blob")) {
std::system("dd if=/dev/urandom of=blob count=16 bs=1M");
}
std::vector<ID> ids;
ids.reserve(fs::file_size("blob") / sizeof(ID));
auto ifs = std::ifstream("blob");
assert(ifs.is_open());
ID id;
while (ifs.read((char*)id.data(), sizeof(id))) {
ids.push_back(id);
}
return ids;
}
TEST(hash, uniform_distribuation) {
constexpr usize BUCKETS = 64;
constexpr float BUCKET_SIZE = static_cast<float>(100) / BUCKETS; // Bucket size in percent.
constexpr float BUCKET_ERR = BUCKET_SIZE * 0.05 /* 5% */; // Allowed distribution error.
const auto ids = read_blob();
usize cnt[BUCKETS] = {0};
for (const auto& id : ids) {
u32 h = hash(id.data(), id.size());
cnt[h % BUCKETS] += 1;
}
for (usize b = 0; b < BUCKETS; ++b) {
const float dist = static_cast<float>(cnt[b]) / ids.size() * 100;
ASSERT_GT(dist, BUCKET_SIZE - BUCKET_ERR);
ASSERT_LT(dist, BUCKET_SIZE + BUCKET_ERR);
// printf("bucket %2ld: %5.2f (%ld)\n", b, dist, cnt[b]);
}
}
TEST(hash, DISABLED_collisions) {
const auto ids = read_blob();
std::unordered_map<u32, usize> hits;
for (const auto& id : ids) {
u32 h = hash(id.data(), id.size());
hits[h] = hits[h] + 1;
}
usize collisions = 0;
for (const auto& hit : hits) {
if (hit.second > 1) {
++collisions;
}
}
printf("Hashed %ld values got %ld collisions\n", ids.size(), collisions);
}
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