Timing sort algorithm

Emiliano

Rate me:

3.35/5 (16 votes)

3 Mar 2003

67.8K

530

Timing fluctuation can limit the usefulness of timing experiments.

Download source files - 1 Kb

Introduction

Timing fluctuation can limit the usefulness of timing experiments. The idea here is to place the algorithm inside a loop and count the number of iterations between ticks.

The reason for using the time function rather then the clock function is because it can be poorly implemented with the result of "missing ticks", and accumulating this over many loops, it will lead to inaccuracy up to 50%. Using the time function and looping in between ticks will decrease the inaccuracy.

Example

time_t start;
start = time(NULL);

vector<long> iterations;

//reps is the nunber of time that the code will loop
iterations.reserve(reps);
    
while(iterations.size() < reps){
        int count = 0;
        do{
            count++;
            copy(A, A+N, B);
            sort(B, B+N);
            //getting end time
            finish = time(NULL);
            //check that the time has changed before
            //going back into loop and increment count 
        }while(start == finish);
        //inserting count value in the vector that indicates the time we 
        //have looped between a tick during time function
        iterations.push_back(count);
        start = finish;
    }

This can then be repeated for several times, so even if the duration between ticks vary, we can select the most accurate.

Output

The output below shows the average result that has been calculated sorting an array of doubles of length 10000 for 10 times.

The result is calculated by retrieving the middle value after the vector has been sorted and dividing it by 1000.0 which will give us the milliseconds.

1000.0/iterations[reps/2]

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

Written By

Emiliano

Web Developer

United Kingdom

This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

// // CElapsed.h - header for the CElapsed class // // Copyright 1998-2003 by Rick York // This class is free for use in any and all applications for any purpose. // // To use this class include this header and do the following : // // CElapsed timer; // instantiate a timer object. // timer.Begin(); // start timing // ... // your code here // double TimeInSeconds = timer.Elapsed(); // obtain elapsed time // #ifndef _CELAPSED_H #define _CELAPSED_H #else #error repeated include of this file #endif class CElapsed { private : double m_Period; int m_Initialized; __int64 m_Frequency; __int64 m_BeginTime; public : CElapsed() // constructor { // get the frequency of the counter m_Initialized = QueryPerformanceFrequency( (LARGE_INTEGER *)&m_Frequency ); if( ! m_Initialized ) m_Period = 0.0; else m_Period = 1.0 / (double)m_Frequency; // save period of clock } BOOL Begin() // start timing { if( ! m_Initialized ) return FALSE; // error - couldn't get frequency // get the starting counter value return QueryPerformanceCounter( (LARGE_INTEGER *)&m_BeginTime ); } double Elapsed() // stop timing and get elapsed time in seconds { // get the ending counter value __int64 endtime; QueryPerformanceCounter( (LARGE_INTEGER *)&endtime ); // determine the elapsed counts __int64 elapsed = endtime - m_BeginTime; // convert counts to time in seconds and return it return (double)elapsed * m_Period; } BOOL Available() // returns true if the perf counter is available { return m_Initialized; } __int64 GetFreq() // return perf counter frequency as large int { return m_Frequency; } };

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

Timing sort algorithm

Introduction

Example

Output

License

Comments and Discussions