获取x86的当前tick总数

int64_t Counter::rdtsc() {
#if defined(__x86_64__)
    int64_t ret = 0;
    uint32_t high = 0;
    uint32_t low = 0;
    __asm__ volatile("rdtsc":"=a"(low), "=d"(high));
    ret = ((int64_t)high << 32) | low;
    return ret;
#elif defined(__i386__)
    int64_t ret = 0;
    __asm__ volatile("rdtsc": "=A"(ret));
    return ret;
#elif defined(__powerpc__)
    uint64_t tbl, tbu0, tbu1;
 
    do {
        __asm__ volatile("mftbu %0" : "=r"(tbu0));
        __asm__ volatile("mftb %0" : "=r"(tbl));
        __asm__ volatile("mftbu %0" : "=r"(tbu1));
    } while (tbu0 !=