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From: shirley@iuvax.cs.indiana.edu (peter shirley)
Newsgroups: comp.lang.c++
Subject: why is this program slow?
Message-ID: <1991Jan9.002244.23398@news.cs.indiana.edu>
Date: 9 Jan 91 05:22:13 GMT
Organization: Computer Science, Indiana University
Lines: 115

I have a C++ program that takes about 170% as long as a similar C program.
I've run it on a vax and a sun with and without big-O.
I've inlined everything I can, and I don't understand the slowdown.
Could someone enlighten me?  (yes, I looked at the C code generated
by CC, and am too dumb to understand it).

The C, then C++ code follow.

Thanks,

Pete Shirley
shirley@cs.indiana.edu

**************** begin C code *********************

#include "stdio.h"


main()
{
    int i;
    double a[3], b[3]; 

    a[0] = a[1] = a[2] = 0.0;
    b[0] = 1.0;
    b[1] = 2.0;
    b[2] = 4.0;

    for ( i = 0; i < 1000000; i++)
    {
        a[0] = a[0] + b[0];
        a[1] = a[1] + b[1];
        a[2] = a[2] + b[2];
    }

    fprintf(stderr, "%lf %lf %lf\n", a[0], a[1], a[2]);
}


************* end C code *******************

************** begin C++ code *********************

#include <math.h>
#include <stream.h>


class vector {
protected:
    double data[3];
public:
    vector();
    vector(double, double, double);
    void set(double, double, double);
    void operator=(vector&);
    friend ostream& operator<<(ostream&, vector&);
    friend vector operator+(vector&, vector&);
};


inline vector::vector()
{
}


inline vector::vector(double a, double b, double c)
{
   data[0] = a;  data[1] = b;  data[2] = c;
}


inline void vector::set(double a, double b, double c)
{
   data[0] = a;  data[1] = b;  data[2] = c;
}

inline void vector::operator=(vector& v)
{

   data[0] = v.data[0];
   data[1] = v.data[1];
   data[2] = v.data[2];

}



inline vector operator+(vector& u, vector& v)
{
    vector temp;

    temp.data[0] = u.data[0] + v.data[0];
    temp.data[1] = u.data[1] + v.data[1];
    temp.data[2] = u.data[2] + v.data[2];
    return temp;
}

inline ostream& operator<<(ostream& s, vector& t)
{
   return s << "(" << t.data[0] << ", "<< t.data[1] <<", " << t.data[2] <<")";
}


main()
{
    vector a(0.0, 0.0, 0.0);
    vector b(1.0, 2.0, 4.0);

    for (int i = 0; i < 1000000; i++)
        a = a + b;

    cerr << a << "\n";
}

************** end C++ code ***********************