floats_are_slow.c

#include <stdio.h>
#include <sys/time.h>

int repetitions = 100000000;

double time_diff(struct timeval x, struct timeval y);

double native_add(double a, double b) {
    double x;
    
    int i;
    for (i = 1; i <= repetitions; i++) {
        x = a + b;
    }
    return x;
}

void native() {
    struct timeval before, after;
    gettimeofday(&before, NULL);
    
    double x;
    x = native_add(1.11, 1.19);
    
    gettimeofday(&after, NULL);
    printf("native answer: %f\n", x);
    
    printf("Total time elapsed: %.0lf us\n", time_diff(before, after));
};

double twoints_add(double a, double b) {
    int xa, xb, aa, ab, ba, bb;
    int precision = 1000;
    aa = (int)a;
    ab = (int)(a * precision)-(aa * precision);
    ba = (int)b;
    bb = (int)(b * precision)-(ba * precision);
    
    int i;
    for (i = 1; i <= repetitions; i++) {
        xa = aa + ba;
        xb = ab + bb;
    }
    
    double result;
    result = (double)xa;
    result = result + ((double)xb / precision);
    
    return result;
}

void twoints() {
    struct timeval before, after;
    gettimeofday(&before, NULL);
    
    double x;
    x = twoints_add(1.11, 1.19);
    
    gettimeofday(&after, NULL);
    printf("twoints answer: %f\n", x);
    
    printf("Total time elapsed: %.0lf us\n", time_diff(before, after));
};


int main() {
    native();
    twoints();
    return 0;
}
 
double time_diff(struct timeval x, struct timeval y) {
    double x_ms, y_ms, diff;
    
    x_ms = (double)x.tv_sec * 1000000 + (double)x.tv_usec;
    y_ms = (double)y.tv_sec * 1000000 + (double)y.tv_usec;
    
    diff = (double)y_ms - (double)x_ms;
    
    return diff;
}