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#include <chrono>
#include <random>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <intrin.h>
#pragma intrinsic(_BitScanReverse)
int prevent_optimization = 0;
template <typename T, T d, T M> __forceinline T floor_log_2_bisT(T n)
{
T tmp = (1 << d);
// int _d = d; int _res = M; // pour voir les params
if (M != 0) {
if (n < tmp) {
return floor_log_2_bisT<T, d - M, M / 2>(n);
}
else {
return floor_log_2_bisT<T, d + M, M / 2>(n);
}
}
else {
if (n < tmp) {
return d;
}
else {
return d + 1;
}
}
}
template <typename T> T _floor_log_2(T n) {
T res = floor_log_2_bisT<T, sizeof(T)* 4, sizeof(T)* 2>(n);
return res;
}
unsigned int floor_log_2_binary_unroll(unsigned int n) {
return _floor_log_2<unsigned int>(n);
}
int floor_log_2_binary_naive(unsigned int n) {
int nb_bit_for_type = sizeof(int)* 8;
int M = nb_bit_for_type / 4;
int d = nb_bit_for_type / 2;
int res = 0;
while (M) {
int tmp = 1 << d;
if (n < tmp) {
d -= M;
}
else {
d += M;
}
M = M / 2;
}
int tmp = 1 << d;
if (n >= tmp) {
d += 1;
}
return d;
}
int floor_log_2_naive(unsigned int t)
{
int r = 1;
while (t >>= 1)
{
r++;
}
return r;
}
int floor_log_2_intrinsic(unsigned int t)
{
if (t == 0)
return 1;
unsigned long r;
_BitScanReverse(&r, t);
return r + 1;
}
int floor_log_2_intrinsic_noz(unsigned int t)
{
// give random result if t == 0
unsigned long r = 0;
_BitScanReverse(&r, t);
return r + 1;
}
template <class Rep, class Period>
int to_ms(const std::chrono::duration<Rep, Period>& d)
{
return std::chrono::duration_cast<std::chrono::milliseconds>(d).count();
}
template <typename Func>
void Do(const std::string& desc, const std::vector<int>& v, Func f)
{
std::chrono::system_clock clock;
int res = 0;
auto start = clock.now();
for (int i : v)
{
res += f(i);
}
auto end = clock.now();
prevent_optimization += res;
std::cout << std::left << std::setw(25) << desc;
std::cout << " : " << to_ms(end - start) << " ms" << std::endl;
}
int pick_a_number(int min, int max)
{
static std::default_random_engine rng;
std::uniform_int_distribution<> d(min, max);
return d(rng);
}
void test(int nbint, int min, int max)
{
std::cout << min << " " << max << std::endl;
std::vector<int> v;
for (int i = 0; i < nbint; i++)
{
v.push_back(pick_a_number(min, max));
}
Do("floor_log_2_naive", v, &floor_log_2_naive);
Do("floor_log_2_binary_naive", v, &floor_log_2_binary_naive);
Do("floor_log_2_binary_unroll", v, &floor_log_2_binary_unroll);
Do("floor_log_2_intrinsic", v, &floor_log_2_intrinsic);
Do("floor_log_2_intrinsic_noz", v, &floor_log_2_intrinsic_noz);
std::cout << std::endl;
}
int main()
{
int nbitem = 100000000;
for (int i = 0; i < 31; i++)
test(nbitem, 0, 1 << i);
std::cout << prevent_optimization;
return 0;
} |
aider l'optimiseur pour floor_log_2(n)
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Envoyé par acx01b
A méditer: La solution la plus simple est toujours la moins compliquée
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