Instruction order in C/C++, C (gcc)

Instruction order in C/C++

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

int compute1 (char a[], int start, int end) {
    int sum = 0;
    int min = a[start];
    int max = a[start];

for (int i = start; i < end; i++) {
        if (a[i] > max) max = a[i];
        if (a[i] < min) min = a[i];

int cube = a[i] * a[i] * a[i];
        sum += cube;
    }

return sum;
}

int compute2 (char a[], int start, int end) {
    int sum = 0;
    int min = a[start];
    int max = a[start];

for (int i = start; i < end; i++) {
        int cube = a[i] * a[i] * a[i];
        sum += cube;
        
        if (a[i] > max) max = a[i];
        if (a[i] < min) min = a[i];
    }

return sum;
}

void initArray (char * array, int size) {
  int intsInArray = size / sizeof(int);
  int trailing = size % sizeof(int);
  int * arr = (int *) array;
  
  int i;
  for (i = 0; i < intsInArray; i++) {
    arr[i] = rand();
  }
  
  int random = rand();
  int j;
  i *= 4;
  for (j = 0; j < trailing; j++) {
    char byte = random & 0xFF;
    random >>= 8;
    array[i + j] = byte;
  }   
}

int main (int argc, char *argv[]) {
  struct timeval t0, t1;
  int result;
  int size = 50000000;
  char * array = (char *) malloc(size);
    
  initArray(array, size);
  
  double runtime;
  
  for (int i = 0; i < 2; i++) {
    /* Min/max */
    (void) printf("Min/max first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute1(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n", runtime);
    
    /* Product-sum */
    (void) printf("Product-sum first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute2(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n\n", runtime);
  }
  
  printf("================\n\n");
    
  for (int i = 0; i < 2; i++) {
    /* Product-sum */
    (void) printf("Product-sum first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute2(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n", runtime);
      
    /* Min/max */
    (void) printf("Min/max first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute1(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n\n", runtime);
  }
  
  printf("================\n\n");
    
  for (int i = 0; i < 2; i++) {
    /* Min/max */
    (void) printf("Min/max first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute1(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n", runtime);
      
    /* Product-sum */
    (void) printf("Product-sum first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute2(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n", runtime);
      
    /* Product-sum */
    (void) printf("Product-sum first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute2(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n", runtime);
      
    /* Min/max */
    (void) printf("Min/max first: ");
    gettimeofday(&t0, NULL); // start time
    result = compute1(array, 0, size);
    gettimeofday(&t1, NULL); // end time
    runtime = t1.tv_sec - t0.tv_sec + (t1.tv_usec - t0.tv_usec)/1000000.0;
    (void) printf("Completed in %f sec\n\n", runtime);
  }

free(array);

return 0;
}


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