gistfile1.c

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

double
random_double(void)
{
  char digs[17];
  int i, j;

  for (i = j = 0; i < 15 && j < 17; ++i, ++j) {
    digs[j] = '0' + ((random() >> 16) % 10);
    if (i == j && random()/(double)(0x3fffffff) > 0.5) {
      digs[++j] = '.';
    }
  }
  if (i == j) {
    digs[16] = digs[15];
    digs[15] = '.';
  }
  digs[17] = '\0';

  return strtod(digs, NULL);
}

double
func(double volatile* value)
{
  return *value;
}

int
main(int argc, char** argv)
{
  long const TRIALS = 1000000;

  int i;
  double* numbers;
  struct timeval start, end;
  double consumed;

  srandom(time(NULL));

  numbers = (double*)malloc(sizeof(double) * 2 * TRIALS);
  for (i = 0; i < 2*TRIALS; ++i) {
    numbers[i] = random_double();
  }

  /* add */
  printf("add ... ");
  gettimeofday(&start, NULL);
  for (i = 0; i < TRIALS; ++i) {
    double volatile x = numbers[2*i + 0];
    double volatile y = numbers[2*i + 1];
    double volatile z = x + y;
    func(&z);
  }
  gettimeofday(&end, NULL);
  consumed = end.tv_sec + end.tv_usec / 1000000.0;
  consumed -= start.tv_sec + start.tv_usec / 1000000.0;
  printf("%g [secs]; %g [secs/op]\n", consumed, consumed / (double)TRIALS);

  /* sub */
  printf("sub ... ");
  gettimeofday(&start, NULL);
  for (i = 0; i < TRIALS; ++i) {
    double volatile z = numbers[2*i + 0] - numbers[2*i + 1];
    func(&z);
  }
  gettimeofday(&end, NULL);
  consumed = end.tv_sec + end.tv_usec / 1000000.0;
  consumed -= start.tv_sec + start.tv_usec / 1000000.0;
  printf("%g [secs]; %g [secs/op]\n", consumed, consumed / (double)TRIALS);

  /* mul */
  printf("mul ... ");
  gettimeofday(&start, NULL);
  for (i = 0; i < TRIALS; ++i) {
    double x = numbers[2*i + 0];
    double y = numbers[2*i + 1];
    double z = x * y;
    func(&z);
  }
  gettimeofday(&end, NULL);
  consumed = end.tv_sec + end.tv_usec / 1000000.0;
  consumed -= start.tv_sec + start.tv_usec / 1000000.0;
  printf("%g [secs]; %g [secs/op]\n", consumed, consumed / (double)TRIALS);

  free(numbers);

  return 0;
}