c - How to determine how many times Time Stamp Counter (TSC) is reset -

i need measure time based on time stmp counter (tsc) reasons. read tsc, using code below:

#include <stdio.h> #include <inttypes.h>  inline volatile uint32_t rdtsc32() {     register uint32_t tsc asm("eax");     asm volatile (".byte 15, 49" : : : "eax", "edx");     return tsc; }  inline volatile uint64_t rdtsc64() {     register uint64_t tsc asm("rax");     asm volatile (".byte 15, 49" : : : "rax", "rdx");     return tsc; }   int main() {     while (1) {         printf("%" priu64 "\n", rdtsc64());     } }  

when i've tested it, works fine. except 1 thing. when reaches maximum counter value (some value higher 4,256,448,731, in environment,) counter value gets reset 0 , keeps going on.

in situation, there way see how many times tsc has been reset?

for example, code below not print correct time difference:

#include <stdio.h>  int main() {     long long start, end;     start = rdtsc64();     // long long works     end = rdtsc64();     printf("%lld \n", end - start); }  

the time stamp counter 64-bit, see statement on wipedia page:

the time stamp counter (tsc) 64-bit register present on x86 processors since pentium.

for reason you're getting truncated value 32 bits, why wraps. 64-bit value need 146 years of continuous counting @ 4 ghz wrap.

your code seems want use both eax , edx hold 2 32 bit halves, expected. must go wrong when moving values single c variable. believe snippet you're using gcc; perhaps that's no longer compiler?

inspect generated assembly, , check compiler docs proper intrinsic function instead. this question has answers, compiler-specific assembly.