Re: C++ programming challenge

Hi,

here's my code. StopWatch source needs to be added on top of the file. I
cannot post it as comment on the page because it says my "html tag"
<fstream> is not accepted... Oo...

I would prefer to start the timing *after* the file has been read,
because this way it's too I/O limited.

Regards,

Nils

//////////

#include <fstream>
#include <iostream>

#include <time.h>

using namespace std;

static const size_t g_blockSize = 1024 * 1024; // 1MB

static char g_buf[g_blockSize];

int main(int argc, char* argv[])
{
    if( argc < 2 )
    {
        std::cout << "usage: <app> <text file>" << std::endl;
        return -1;
    }

    unsigned int letterFreq[256];
    memset( letterFreq, 0, sizeof(letterFreq) );

    // start counting time
    CStopWatch s;
    s.startTimer();

    FILE* hFile = fopen( argv[1], "rb" ); // binary mode please

    if( 0 == hFile )
    {
        std::cout << "file << " << argv[1] << "couldn't be opened." << std::endl;
        return -1;
    }

    // count chars
    size_t totalReadAmount = 0;

    size_t countRead = fread( g_buf, 1, g_blockSize, hFile );

    while( countRead > 0 )
    {
        totalReadAmount += countRead;

        // count chars
        int remaining = (int)countRead;

        {
            char* ptr = g_buf;

            size_t n = int(countRead+7)/8;
            switch(countRead&7)
            {
            case 0: do{ letterFreq[ *ptr++ ]++;
            case 7: letterFreq[ *ptr++ ]++;
            case 6: letterFreq[ *ptr++ ]++;
            case 5: letterFreq[ *ptr++ ]++;
            case 4: letterFreq[ *ptr++ ]++;
            case 3: letterFreq[ *ptr++ ]++;
            case 2: letterFreq[ *ptr++ ]++;
            case 1: letterFreq[ *ptr++ ]++;
                    }while( --n > 0 );
            }
        }

        countRead = fread( g_buf, 1, g_blockSize, hFile );
    }

    // compute result in percent
    const double hunderedDivFileSize = 100.0 / double(totalReadAmount);

    for( char i='a'; i<='z'; i++ )
    {
        unsigned int totalLetterFreq = letterFreq[i] + letterFreq[ i + 'A' -
'a' ];

        const double freq = hunderedDivFileSize * double(totalLetterFreq);

        cout << i << ' ' << freq << "%" << std::endl;
    }

    s.stopTimer();

    cout << "Total Time: " << s.getElapsedTime() << std::endl;

    fclose( hFile );

    return 0;
}