r_usage_read.c - shared from CS50 IDE

r_usage_read.c

/**
 * r_usage_read.c
 *
 * The following code is licensed under CC BY-NC-SA 3.0
 * https://creativecommons.org/licenses/by-nc-sa/3.0/
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <fcntl.h>

// 100 MB
#define READAMOUNT 100000000


double calculate(const struct rusage* b, const struct rusage* a);

int main()
{
    // Required structs for getrusage calls
    struct rusage after1, before1, after2, before2;

    int filedes = open("../jpg/card.raw", O_RDONLY);
    void* buf = malloc(READAMOUNT);

    // read READAMOUNT * 1 bytes
    getrusage(RUSAGE_SELF, &before1);
    read(filedes, buf, READAMOUNT);
    getrusage(RUSAGE_SELF, &after1);

    // read 1 * READAMOUNT bytes
    getrusage(RUSAGE_SELF, &before2);
    for (int i = 0; i < READAMOUNT; i++) {
        read(filedes, buf, 1);
    }
    getrusage(RUSAGE_SELF, &after2);

    // Calculate time spent
    double time1 = calculate(&before1, &after1);
    double time2 = calculate(&before2, &after2);

    printf("Time spent reading READAMOUNT * 1 bytes: %f\n", time1);
    printf("Time spent reading 1 * READAMOUNT bytes: %f\n", time2);
}


/**
 * Returns number of seconds between b and a.
 * The following code was written by David J. Malan of Harvard University.
 */
double calculate(const struct rusage* b, const struct rusage* a)
{
    if (b == NULL || a == NULL)
    {
        return 0.0;
    }
    else
    {
        return ((((a->ru_utime.tv_sec * 1000000 + a->ru_utime.tv_usec) -
                 (b->ru_utime.tv_sec * 1000000 + b->ru_utime.tv_usec)) +
                ((a->ru_stime.tv_sec * 1000000 + a->ru_stime.tv_usec) -
                 (b->ru_stime.tv_sec * 1000000 + b->ru_stime.tv_usec)))
                / 1000000.0);
    }
}