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#include <algorithm>
#include <chrono>
#include <cstring>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <random>
#include <string>
#include <tuple>
#include <vector>
char *ndpi_strnstr(const char *s, const char *find, size_t slen) {
char c;
size_t len;
if ((c = *find++) != '\0') {
len = strnlen(find, slen);
do {
char sc;
do {
if (slen-- < 1 || (sc = *s++) == '\0') return (NULL);
} while (sc != c);
if (len > slen) return (NULL);
} while (strncmp(s, find, len) != 0);
s--;
}
return ((char *)s);
}
char *ndpi_strnstr_opt(const char *haystack, const char *needle, size_t len) {
if (!haystack || !needle || len == 0) {
return NULL;
}
size_t needle_len = strlen(needle);
size_t hs_real_len = strnlen(haystack, len);
if (needle_len == 0) {
return (char *)haystack;
}
if (needle_len > hs_real_len) {
return NULL;
}
if (needle_len == 1) {
return (char *)memchr(haystack, *needle, hs_real_len);
}
const char *current = haystack;
const char *haystack_end = haystack + hs_real_len;
while (current <= haystack_end - needle_len) {
current = (const char *)memchr(current, *needle, haystack_end - current);
if (!current) {
return NULL;
}
if ((current + needle_len <= haystack_end) &&
memcmp(current, needle, needle_len) == 0) {
return (char *)current;
}
current++;
}
return NULL;
}
char* ndpi_strnstr_opt2(const char* haystack, const char* needle, size_t length_limit) {
if (!haystack || !needle) {
return nullptr;
}
const size_t needle_len = strlen(needle);
if (needle_len == 0) {
return (char*) haystack;
}
const size_t hs_real_len = strnlen(haystack, length_limit);
if (needle_len == 1) {
return (char *)memchr(haystack, *needle, hs_real_len);
}
if (needle_len > hs_real_len) {
return nullptr;
}
const char*const end_of_search = haystack + hs_real_len - needle_len + 1;
const char *current = haystack;
while (current < end_of_search) {
current = (const char*) memchr(current, *needle, end_of_search - current);
if (!current) {
return nullptr;
}
if (memcmp(current, needle, needle_len) == 0) {
return (char*) current;
}
++current;
}
return nullptr;
}
std::string random_string(size_t length, std::mt19937 &gen) {
std::uniform_int_distribution<> dis(0, 255);
std::string str(length, 0);
for (size_t i = 0; i < length; i++) {
str[i] = static_cast<char>(dis(gen));
}
return str;
}
double measure_time(const std::function<char *(const char *, const char *,
size_t)> &strnstr_impl,
const std::string &haystack, const std::string &needle) {
auto start = std::chrono::high_resolution_clock::now();
volatile auto result =
strnstr_impl(haystack.c_str(), needle.c_str(), haystack.size());
auto end = std::chrono::high_resolution_clock::now();
return std::chrono::duration_cast<std::chrono::nanoseconds>(end - start)
.count();
}
void warm_up(const std::function<char *(const char *, const char *, size_t)>
&strnstr_impl,
const std::string &haystack, const std::string &needle,
int iterations) {
for (int i = 0; i < iterations; i++) {
volatile auto result =
strnstr_impl(haystack.c_str(), needle.c_str(), haystack.size());
}
}
double average_without_extremes(const std::vector<double> ×) {
if (times.size() < 5) {
return std::accumulate(times.begin(), times.end(), 0.0) /
static_cast<double>(times.size());
}
auto sorted_times = times;
std::sort(sorted_times.begin(), sorted_times.end());
sorted_times.erase(sorted_times.begin());
sorted_times.pop_back();
return std::accumulate(sorted_times.begin(), sorted_times.end(), 0.0) /
sorted_times.size();
}
int main() {
std::ios_base::sync_with_stdio(false);
std::mt19937 gen(std::random_device{}());
const std::vector<size_t> haystack_lengths = {
128, 256, 368, 448, 512, 640, 704, 768, 832, 896,
960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472};
const std::vector<size_t> needle_lengths = {5, 10, 15, 20, 25, 30,
35, 40, 45, 50, 55, 60};
const std::vector<std::pair<
std::string, std::function<char *(const char *, const char *, size_t)>>>
strnstr_impls = {
{"ndpi_strnstr", ndpi_strnstr},
{"ndpi_strnstr_opt", ndpi_strnstr_opt},
{"ndpi_strnstr_opt2", ndpi_strnstr_opt2},
};
const int iterations = 100000;
const int warm_up_iterations = 1000;
for (size_t haystack_len : haystack_lengths) {
for (size_t needle_len : needle_lengths) {
std::cout << "\nTest case - Haystack length: " << haystack_len
<< ", Needle length: " << needle_len << "\n";
std::string haystack = random_string(haystack_len, gen);
std::string needle = random_string(needle_len, gen);
std::map<std::string, double> times;
for (const auto &impl : strnstr_impls) {
warm_up(impl.second, haystack, needle, warm_up_iterations);
std::vector<double> times_vector;
for (int i = 0; i < iterations; i++) {
times_vector.push_back(measure_time(impl.second, haystack, needle));
}
double average_time = average_without_extremes(times_vector);
times[impl.first] = average_time;
std::cout << "Average time for " << impl.first << ": " << average_time
<< " ns\n";
}
std::string fastest_impl;
double fastest_time = std::numeric_limits<double>::max();
for (const auto &impl_time : times) {
if (impl_time.second < fastest_time) {
fastest_impl = impl_time.first;
fastest_time = impl_time.second;
}
}
for (const auto &impl_time : times) {
if (impl_time.first != fastest_impl) {
std::cout << fastest_impl << " is " << impl_time.second / fastest_time
<< " times faster than " << impl_time.first << "\n";
}
}
}
}
return 0;
}
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