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StreamGetSzPtr

 

Using Stream::GetSzPtr to optimize the algorithm to count lines in Stream

 

 

StreamGetSzPtr.cpp

 

#include <Core/Core.h>

 

using namespace Upp;

 

int CountLines(Stream& s)

{

    int n = 0;

    int c;

    while((c = s.Get()) >= 0)

        n += c == '\n';

    return n;

}

 

int CountLinesOptimized(Stream& s)

{

    int n = 0;

    for(;;) {

        int sz;

        const byte *p = s.GetSzPtr(sz);

        if(sz) {

            const byte *e = p + sz;

            const byte *e4 = p + (sz & ~3);

            while(p < e4) {

                n += (p[0] == '\n' || p[1] == '\n' || p[2] == '\n' || p[3] == '\n');

                p += 4;

            }

            while(p < e)

                n += *p++ == '\n';

        }

        else {

            int c = s.Get();

            if(c < 0)

                return n;

            n += c == '\n';

        }

    }

    return n;

}

 

CONSOLE_APP_MAIN

{

    StdLogSetup(LOG_FILE|LOG_COUT);

    

    const Vector<String>& arg = CommandLine();

    if(arg.GetCount() == 0) {

        RLOG("Please provide testing file path as argument, preferably >500MB");

        return;

    }

    

    {

        RTIMESTOP("Simple");

        FileIn in(arg[0]);

        RDUMP(CountLines(in));

    }

 

    {

        RTIMESTOP("Optimized");

        FileIn in(arg[0]);

        RDUMP(CountLinesOptimized(in));

    }

}

 

 

 

 

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