struct timeval 和 struct timespec

1. 使用timeval，微秒级（1s = 1 000ms = 1 000 000us = 1 000 000 000ns)

struct timeval
{long tv_sec;  //secondslong tv_usec; //microseconds
}

具体应用:

#include<time.h>
#include<sys/time.h>struct timeval T0,T1;
double ellapsedT = 0;gettimeofday(&T0, NULL);  XX_gen(key);gettimeofday(&T1, NULL); ellapsedT += (T1.tv_sec-T0.tv_sec) + (double)(T1.tv_usec-T0.tv_usec) / (1e+6);printf("\nTime for XX_gen is %fs\n", ellapsedT);

2. 使用timespec，纳秒级

typedef long time_t;
#ifndef _TIMESPEC
#define _TIMESPECstruct timespec
{time_t tv_sec; // secondslong tv_nsec; // nanoseconds
};#endif

具体使用：

struct timespec start, end; //nanoseconds
double time_gen;
time_gen = 0.0;clock_gettime(CLOCK_MONOTONIC, &start);XX_gen(key);clock_gettime(CLOCK_MONOTONIC, &end);time_gen += (double) (1000 * (end.tv_sec - start.tv_sec)) + (double) (end.tv_nsec - start.tv_nsec)/1000000;printf("\nTime for XX_gen is %8.6f mSec. \n",  time_gen);

3. 获得CPU周期数

uint64_t rdtsc()
{uint32_t hi, lo;__asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));return ( (uint64_t)lo)|( ((uint64_t)hi)<<32 );
}

/* timing */
#ifdef WIN#define current_stamp(a)  __asm__ __volatile__("rdtsc":"=a"(((unsigned int *)(a))[0]),"=d"(((unsigned int *)a)[1]))
#else#define current_stamp(a)  __asm__ __volatile__("rdtsc":"=a"(((unsigned int *)(a))[0]),"=d"(((unsigned int *)a)[1]))
#endiftypedef unsigned long long DWORD; /* Should be 64-bit = 8 bytes */ DWORD start_cycle, end_cycle, CPU_cycles = 0;
double ellapsedT = 0;double CPU_GHz, T_cycles_per_byte;current_stamp(&start_cycle);
gettimeofday(&T0, NULL);  XX_gen(key);gettimeofday(&T1, NULL);
current_stamp(&end_cycle); CPU_cycles += end_cycle-start_cycle; ellapsedT += (T1.tv_sec-T0.tv_sec) + (double)(T1.tv_usec-T0.tv_usec) / (1e+6);CPU_GHz = CPU_cycles/(1e+9)/ellapsedT;  T_cycles_per_byte = ((double)CPU_cycles/0xC7); printf("\nDetected effective CPU speed is %lf GHz.\n", CPU_GHz);printf("\nSpeed is %.2lf cycles per byte for XX_gen.\n", T_cycles_per_byte);printf("\nTime for XX_gen is %fs\n", ellapsedT);

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