ceph/src/boost/libs/multiprecision/performance/cpp_bin_float_conversion_performance.cpp

   1 #include <boost/multiprecision/cpp_bin_float.hpp>
   2 #include <boost/math/special_functions.hpp>
   3 #include <boost/chrono.hpp>
   4 #include <boost/random/mersenne_twister.hpp>
   5 #include <boost/random/uniform_int.hpp>
   6
   7 template <class Clock>
   8 struct stopwatch
   9 {
  10    typedef typename Clock::duration duration;
  11    stopwatch()
  12    {
  13       m_start = Clock::now();
  14    }
  15    duration elapsed()
  16    {
  17       return Clock::now() - m_start;
  18    }
  19    void reset()
  20    {
  21       m_start = Clock::now();
  22    }
  23
  24 private:
  25    typename Clock::time_point m_start;
  26 };
  27
  28 template <class T>
  29 T generate_random()
  30 {
  31    typedef int e_type;
  32    static boost::random::mt19937 gen;
  33    T val = gen();
  34    T prev_val = -1;
  35    while(val != prev_val)
  36    {
  37       val *= (gen.max)();
  38       prev_val = val;
  39       val += gen();
  40    }
  41    e_type e;
  42    val = frexp(val, &e);
  43
  44    static boost::random::uniform_int_distribution<e_type> ui(-20, 20);
  45    return ldexp(val, ui(gen));
  46 }
  47
  48
  49 template <typename T>
  50 double my_convert_to_double(const T& x)
  51 {
  52    double ret = 0;
  53    if(isfinite(x)) {
  54       if(x.backend().exponent() >= -1023 - 52 && x != 0) {
  55          if(x.backend().exponent() <= 1023) {
  56             int e = x.backend().exponent();
  57             T y = ldexp(abs(x), 55 - e);
  58             T t = trunc(y);
  59             int64_t ti = t.template convert_to<int64_t>();
  60             if((ti & 1) == 0) {
  61                if(t < y)
  62                   ti |= 1;
  63             }
  64             if(e >= -1023 + 1) {
  65                ret = ldexp(double(ti), e - 55);
  66             }
  67             else {
  68                // subnormal
  69                typedef boost::multiprecision::number<boost::multiprecision::cpp_bin_float<128, boost::multiprecision::backends::digit_base_2> > cpp_bin_float128_t;
  70                cpp_bin_float128_t sx = ldexp(cpp_bin_float128_t(ti), e - 55);
  71                sx += DBL_MIN;
  72                e = -1023 + 1;
  73                cpp_bin_float128_t sy = ldexp(sx, 55 - e);
  74                cpp_bin_float128_t st = trunc(sy);
  75                ti = st.convert_to<int64_t>();
  76                if((ti & 1) == 0) {
  77                   if(st < sy)
  78                      ti |= 1;
  79                }
  80                ret = ldexp(double(ti), e - 55) - DBL_MIN;
  81             }
  82          }
  83          else {
  84             // overflow
  85             ret = HUGE_VAL;
  86          }
  87       }
  88    }
  89    else {
  90       if(isnan(x))
  91          return nan("");
  92       // inf
  93       ret = HUGE_VAL;
  94    }
  95    return x.backend().sign() ? -ret : ret;
  96 }
  97
  98
  99 template <class T>
 100 void test_conversion_time(const char* name)
 101 {
 102    std::cout << "Testing times for type: " << name << "\n";
 103    std::vector<T> values;
 104
 105    for(unsigned i = 0; i < 10000000; ++i)
 106    {
 107       values.push_back(generate_random<T>());
 108    }
 109
 110    boost::chrono::duration<double> time;
 111    stopwatch<boost::chrono::high_resolution_clock> c;
 112
 113    double total = 0;
 114
 115    for(typename std::vector<T>::const_iterator i = values.begin(); i != values.end(); ++i)
 116    {
 117       total += my_convert_to_double(*i);
 118    }
 119
 120    time = c.elapsed();
 121    std::cout << std::setprecision(3) << std::fixed;
 122    std::cout << "Reference time: " << std::setw(7) << std::right << time << " (total sum = " << total << ")" << std::endl;
 123
 124    c.reset();
 125
 126    total = 0;
 127
 128    for(typename std::vector<T>::const_iterator i = values.begin(); i != values.end(); ++i)
 129    {
 130       total += i->template convert_to<double>();
 131    }
 132
 133    time = c.elapsed();
 134    std::cout << "Boost time:     " << std::setw(7) << std::right << time << " (total sum = " << total << ")" << std::endl;
 135
 136
 137 }
 138
 139
 140 int main()
 141 {
 142    using namespace boost::multiprecision;
 143
 144    test_conversion_time<cpp_bin_float_double>("cpp_bin_float_double");
 145    test_conversion_time<cpp_bin_float_quad>("cpp_bin_float_quad");
 146    test_conversion_time<cpp_bin_float_50>("cpp_bin_float_50");
 147    test_conversion_time<cpp_bin_float_100>("cpp_bin_float_100");
 148
 149    return 0;
 150 }
 151