/*

    File:       MapLargeFile.c

    Description: Shows a technique for accessing files > 4GB in size.

    Copyright:  © Copyright 2003 Apple Computer, Inc. All rights reserved.

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    Change History (most recent first):

*/

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#include <sys/time.h>

#include <unistd.h>

#include <fcntl.h>

#include <sys/types.h>

#include <sys/mman.h>

struct timeval lastTime, thisTime;

/* 

    This sample is set up to map a 6GB file into memory in 256MB chunks.

*/

#define kFileSize (0x180000000ULL)  // size of file we expect to map = 6GB

#define kBufferSize (0x10000000UL)  // we will map it in 256MB chunks

int main( int argc, const char *argv[] )

{

    int                 fd, cnt, loops;

    unsigned long long  *buffer, sum;

    off_t               offset;

    if ( argc != 2 )

    {

        fprintf( stderr, "usage: %s filename\n", argv[0] );

        return -1;

    } 

    // open the file

    fd = open( argv[1], O_RDONLY, 0 );

    if ( fd == 0 )

    {

        fprintf( stderr, "%s: failed to open %s for read\n", argv[0], argv[1] );

        return -1;

    }

    sum = 0;

    offset = 0;

    loops = 9;  // loop through the file 10 times

    gettimeofday( &lastTime, NULL );

    while ( 1 ) // loop for ever, loop exit is handled below

    {        

        // map in a kBufferSize segment of the file

        buffer = mmap( 0, kBufferSize, PROT_READ, MAP_FILE, fd, offset );

        if ( buffer == MAP_FAILED )

        {

            fprintf( stderr, "%s: failed to mmap file at offset 0x%llx\n", argv[0], offset );

            break;

        }

        // touch every byte in this segment of the file.

        // this 'warms up' the pages in memory so that subsequent accesses will be much faster

        for ( cnt = 0; cnt < kBufferSize /  sizeof(sum); cnt += 16 )

        {

            sum += buffer[cnt + 0];

            sum += buffer[cnt + 1];

            sum += buffer[cnt + 2];

            sum += buffer[cnt + 3];

            sum += buffer[cnt + 4];

            sum += buffer[cnt + 5];

            sum += buffer[cnt + 6];

            sum += buffer[cnt + 7];

            sum += buffer[cnt + 8];

            sum += buffer[cnt + 9];

            sum += buffer[cnt + 10];

            sum += buffer[cnt + 11];

            sum += buffer[cnt + 12];

            sum += buffer[cnt + 13];

            sum += buffer[cnt + 14];

            sum += buffer[cnt + 15];

        }

        // unmap the current segment of the file

        munmap( buffer, kBufferSize );

        // increment the offset into the file

        offset += kBufferSize;  

        if ( offset >= kFileSize )

        {

            offset = 0;   // reset the offset if we're at the end of the file

            gettimeofday( &thisTime, NULL );

            printf( "Time = %u seconds, sum = %llx\n", thisTime.tv_sec - lastTime.tv_sec, sum );

            if ( loops-- == 0 ) break;  // exit if we've done all loops.

            lastTime = thisTime;

        }

    }

  close( fd );  // all done, close the file

  return 0;

}