Read Time Stamp Counter from Intel x86 CPU

rdtsc.c

#include <stdio.h>

int main (int argc, const char * argv[]) {
    unsigned int hi;
    unsigned int lo;
    long double result;
    
    /* Set *hi and *lo to the high and low order bits  of the cycle counter.  
       Implementation requires assembly code to use the rdtsc instruction. */
    asm("rdtsc; movl %%edx,%0; movl %%eax,%1"   /* Read cycle counter */
        : "=r" (hi), "=r" (lo)                  /* and move results to */
        : /* No input here */                   /* the two outputs */
        : "%edx", "%eax");
    
    /* Computer result. Use 2^30*2^2 instead of 2^32 to avoid overflow */
    result = ((long double) hi) * (1 << 30) * 4 + ((long double) lo);
    
    /* Output the result */
    printf("%.0Lf", result);
    
    return (0);
}