数据对齐与代码优化笔记

/*************************************************************************
    > File Name: test_align.c
    > Author: dingzhengsheng
    > Mail: dingzs3@asiainfo.com 
    > Created Time: 2015年04月22日 星期三 15时49分08秒
 ************************************************************************/

#include<stdio.h>
#include<stdint.h>
#include<time.h>
#include<stdlib.h>
#include <unistd.h>
#include<string.h>
#include<sys/time.h>
#include<sys/resource.h>


#define SECTOUSEC 1000000
#define ARR_LEN 10000000
#define OP |

//#define DZSTEST

#ifdef DZSTEST
#pragma pack (push)
#pragma pack (1)

struct notalignstruct
{
        char a;
        char b;
        char c;
        uint32_t d;
};
#pragma pack (pop)

struct alignstruct
{
        char a;
        char b;
        char c;
        uint32_t d;
};
#else


struct notalignstruct
{
        char a;
        uint32_t d;
        short int c;
};

struct alignstruct
{
        char a;
        short int c;
        uint32_t d;
};

#endif

void case_one(struct notalignstruct *array, uint32_t array_len, uint32_t *sum)
{
        uint32_t value = 1;
        uint32_t i;
        for(i=0; i<array_len; i++)
                value = value OP array[i].d;

        *sum = *sum OP value;
}
void case_two(struct alignstruct *array, uint32_t array_len, uint32_t *sum)
{
        uint32_t value = 1;
        uint32_t i;
        for(i=0; i<array_len; i++)
                value = value OP array[i].d;

        *sum = *sum OP value;
}

void case_two_yh1(struct alignstruct *array, uint32_t array_len, uint32_t *sum)
{
        uint32_t value = 1;
        uint32_t i;
        uint32_t length = array_len - (array_len&0x3);
        for(i=0; i<length; i+=4)
        {
                value = value OP array[i].d;
                value = value OP array[i+1].d;
                value = value OP array[i+2].d;
                value = value OP array[i+3].d;
        }

        for(; i<length; i+=4)
                value = value OP array[i].d;
        *sum = *sum OP value;
}

void case_two_yh2(struct alignstruct *array, uint32_t array_len, uint32_t *sum)
{
        uint32_t value = 1;
        uint32_t i;
        uint32_t length = array_len - (array_len&0x3);
        uint32_t value1,value2;

        for(i=0; i<length; i+=4)
        {
                value1 = array[i].d OP array[i+1].d;
                value2 = array[i+2].d OP array[i+3].d;
                value = value1 OP value2;
        }

        for(; i<length; i+=4)
                value = value OP array[i].d;
        *sum = *sum OP value;
}

void case_two_yh3(struct alignstruct *array, uint32_t array_len, uint32_t *sum)
{
        register uint32_t value = 1;
        register uint32_t i;
        uint32_t length = array_len - (array_len&0x3);
        uint32_t value1,value2;

        for(i=0; i<length; i+=4)
        {
                value1 = array[i].d OP array[i+1].d;
                value2 = array[i+2].d OP array[i+3].d;
                value = value1 OP value2;
        }

        for(; i<length; i+=4)
                value = value OP array[i].d;
        *sum = *sum OP value;
}


long int get_diff_time(struct timeval *tv1, struct timeval *tv2)
{

   long int n;

   n = tv2->tv_sec*SECTOUSEC + tv2->tv_usec - tv1->tv_sec*SECTOUSEC - tv1->tv_usec;
   return n;
}


void main()
{
        void *p;
        struct notalignstruct *array = malloc(sizeof(struct notalignstruct) * ARR_LEN);
        struct alignstruct *arr = malloc(sizeof(struct alignstruct) * ARR_LEN);
        uint32_t sum;
        struct timeval tv1,tv2;
        time_t timep;
        struct timezone tz;

        time(&timep);
        printf("数据对齐的影响比较：\n");
        gettimeofday(&tv1,NULL);
        case_one(array, ARR_LEN, &sum);
        gettimeofday(&tv2,NULL);
        printf("sizeof(not)=%u : %ld\n",sizeof(struct notalignstruct),get_diff_time(&tv1, &tv2));


        gettimeofday(&tv1,NULL);
        case_two(arr, ARR_LEN, &sum);
        gettimeofday(&tv2,NULL);
        printf("sizeof(not)=%u : %ld\n",sizeof(struct alignstruct),get_diff_time(&tv1, &tv2));

        printf("代码优化的性能比较：\n");
        gettimeofday(&tv1,NULL);
        case_two_yh1(arr, ARR_LEN, &sum);
        gettimeofday(&tv2,NULL);
        printf("减少cpu循环分支预测数sizeof(align)=%u : %ld\n",sizeof(struct alignstruct),get_diff_time(&tv1, &tv2));



        gettimeofday(&tv1,NULL);
        case_two_yh2(arr, ARR_LEN, &sum);
        gettimeofday(&tv2,NULL);
        printf("提高CPU指令流水线并行计算sizeof(align)=%u : %ld\n",sizeof(struct alignstruct),get_diff_time(&tv1, &tv2));


        gettimeofday(&tv1,NULL);
        case_two_yh3(arr, ARR_LEN, &sum);
        gettimeofday(&tv2,NULL);
        printf("将高频率的数据放入寄存器sizeof(align)=%u : %ld\n",sizeof(struct alignstruct),get_diff_time(&tv1, &tv2));

}