memcpy的速度测试

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想把一组char a[4096]的数组拷贝到short b[6][256]中，尝试过用循环移位的方式，还用中间变量short c[2048]的方式。得出的结论：
1. 移位方式效率最低
2. 借用中间变量，变量如果是局部栈中，那么速度比全局的中间变量速度快，缺点是怕栈溢出。
验证代码如下：

//file name testcpyspeed.c#include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<string.h>#define MTW_VIRTUTALCHNUMS              (2)#define MTW_PHYCHNUMS                   (6)#define MTW_MAXCHNUMS                   (MTW_VIRTUTALCHNUMS+MTW_PHYCHNUMS)#define MTW_SAMPLESSZIE                 (256)typedef short int16_t;int16_t mic_data[MTW_PHYCHNUMS][MTW_SAMPLESSZIE] = {0,};int16_t *mic[MTW_PHYCHNUMS] = {0,};//int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t output[MTW_SAMPLESSZIE] = {0,};static int mmap_mwsrchannel(char *databuff,int len){        int i=0;        if(len<4096){                printf("ERROR: %s %d error: length:%d\n",__func__,__LINE__,len);\                return  -1;        }        for( i = 0; i < 256; i++){                mic_data[0][i] = ((databuff[i * 16])|(databuff[i * 16 +1 ]<<8));                mic_data[1][i] = ((databuff[i * 16+1*2])|(databuff[i * 16 +1*2 +1 ]<<8));                mic_data[2][i] = ((databuff[i * 16 +2*2])|(databuff[i * 16 +2*2 +1]<<8));                mic_data[3][i] = ((databuff[i * 16+3*2])|(databuff[i * 16 +3*2 +1 ]<<8));                ref_fft[i]=((databuff[i * 16 + 4*2])|(databuff[i * 16 + 4*2 +1]<<8));                mic_data[4][i] = ((databuff[i * 16 + 6 * 2 ])|(databuff[i * 16 + + 6 *2 +1 ]<<8));                              mic_data[5][i] = ((databuff[i * 16 + 7 * 2 ])|(databuff[i * 16 + 7 * 2 +1 ]<<8));        }        return 0;}void record_to_buff(char *buff,int len){        int i=0;        for(i=0;i<len;i++){                buff[i]=i%256;        }}int main(int argc,char *argv[]){        int i=0;        int len=atoi(argv[1]);        char *buff=malloc(4096);        for(i=0;i<len;i++){                record_to_buff(buff,4096);                mmap_mwsrchannel(buff,4096);        }        return 0;}

linjuntao@linjuntao:~/Desktop/proctice/chartoshort$ cat teststos.c #include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<string.h>#define MTW_VIRTUTALCHNUMS              (2)#define MTW_PHYCHNUMS                   (6)#define MTW_MAXCHNUMS                   (MTW_VIRTUTALCHNUMS+MTW_PHYCHNUMS)#define MTW_SAMPLESSZIE                 (256)typedef short int16_t;int16_t mic_data[MTW_PHYCHNUMS][MTW_SAMPLESSZIE] = {0,};int16_t *mic[MTW_PHYCHNUMS] = {0,};//int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t output[MTW_SAMPLESSZIE] = {0,};static int mmap_mwsrchannel(char *databuff,int len){        int i=0;        if(len<4096){                printf("ERROR: %s %d error: length：%d\n",__func__,__LINE__,len);\                return  -1;        }        int16_t data[2048];        memcpy(data,databuff,4096);        for( i = 0; i < 256; i++){                mic_data[0][i] = data[i * 8 ];                mic_data[1][i] = data[i * 8 + 1 ];                mic_data[2][i] = data[i * 8 + 2];                mic_data[3][i] = data[i * 8 +3];                ref_fft[i]=data[i * 8 + 4];                mic_data[4][i] = data[i * 8 + 6];                mic_data[5][i] = data[i * 8 + 7];         }        return 0;}void record_to_buff(char *buff,int len){        int i=0;        for(i=0;i<len;i++){                buff[i]=i%256;        }}int main(int argc,char *argv[]){        int i=0;        int len=atoi(argv[1]);        char *buff=malloc(4096);        for(i=0;i<len;i++){                record_to_buff(buff,4096);                mmap_mwsrchannel(buff,4096);        }        return 0;}

linjuntao@linjuntao:~/Desktop/proctice/chartoshort$ cat teststoglobals.c #include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<string.h>#define MTW_VIRTUTALCHNUMS              (2)#define MTW_PHYCHNUMS                   (6)#define MTW_MAXCHNUMS                   (MTW_VIRTUTALCHNUMS+MTW_PHYCHNUMS)#define MTW_SAMPLESSZIE                 (256)typedef short int16_t;int16_t mic_data[MTW_PHYCHNUMS][MTW_SAMPLESSZIE] = {0,};int16_t *mic[MTW_PHYCHNUMS] = {0,};//int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t ref_fft[MTW_SAMPLESSZIE] = {0,};int16_t output[MTW_SAMPLESSZIE] = {0,};int16_t data[2048];static int mmap_mwsrchannel(char *databuff,int len){        int i=0;        if(len<4096){                printf("ERROR: %s %d error: length：%d\n",__func__,__LINE__,len);\                return  -1;        }        memcpy(data,databuff,4096);        for( i = 0; i < 256; i++){                mic_data[0][i] = data[i * 8 ];                mic_data[1][i] = data[i * 8 + 1 ];                mic_data[2][i] = data[i * 8 + 2];                mic_data[3][i] = data[i * 8 +3];                ref_fft[i]=data[i * 8 + 4];                mic_data[4][i] = data[i * 8 + 6];                mic_data[5][i] = data[i * 8 + 7];         }        return 0;}void record_to_buff(char *buff,int len){        int i=0;        for(i=0;i<len;i++){                buff[i]=i%256;        }}int main(int argc,char *argv[]){        int i=0;        int len=atoi(argv[1]);        char *buff=malloc(4096);        for(i=0;i<len;i++){                record_to_buff(buff,4096);                mmap_mwsrchannel(buff,4096);        }        return 0;}

//编译:cc testcpyspeed.c -o testor ;gcc teststos.c -o test16_16  ; gcc teststoglobals.c  -o teststoglobals//验证:linjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./testor 200000real    0m1.999suser    0m1.996ssys     0m0.000slinjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./test16_16 200000real    0m1.661suser    0m1.660ssys     0m0.000slinjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./teststoglobals 200000real    0m1.658suser    0m1.656ssys     0m0.000slinjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./test16_16 4000000real    0m33.031suser    0m33.028ssys     0m0.000slinjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./teststoglobals 4000000real    0m33.157suser    0m33.156ssys     0m0.000slinjuntao@linjuntao:~/Desktop/proctice/chartoshort$ time ./testor 4000000real    0m40.298suser    0m40.292ssys     0m0.004s

如果执行频率比较高，还是使用局部临时变量拷贝比较快。

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