ex23.c

#include <stdio.h>
#include <string.h>
#include "dbg.h"

int normal_copy(char *from,char *to,int count)
{
    int i=0;
    for(i=0;i<count;i++){
        to[i]=from[i];
    }

    return i;
}

int duffs_device(char *from,char *to,int count)
{
    {
        int n=(count+7)/8;
        switch(count%8){
            case 0:do{
                *to++=*from++;
                case 7:*to++=*from++;
                case 6:*to++=*from++;
                case 5:*to++=*from++;
                case 4:*to++=*from++;
                case 3:*to++=*from++;
                case 2:*to++=*from++;
                case 1:*to++=*from++;
            }while(--n>0);
        }
    }

    return count;
}

int zeds_device(char *from,char *to,int count)
{
    {
        int n=(count+7)/8;
        switch(count%8){
            case 0:
            again:*to++=*from++;

            case 7:*to++=*from++;
            case 6:*to++=*from++;
            case 5:*to++=*from++;
            case 4:*to++=*from++;
            case 3:*to++=*from++;
            case 2:*to++=*from++;
            case 1:*to++=*from++;
                       if(--n>0) goto again;
        }
    }

    return count;
}

int valid_copy(char *data,int count,char expects)      //验证main里的memset以及复制函数是否有效
{
    int i=0;
    for(i=0;i<count;i++){
        if(data[i]!=expects){
            log_err("[%d]%c!=%c",i,data[i],expects);
            return 0;
        }
    }

    return 1;
}

int main(int argc, char *argv[])
{
    char from[1000]={'a'};
    char to[1000]={'c'};
    int rc=0;

    // setup the from to have some stuff
    memset(from,'x',1000);       //memset把from字符串中的前1000位设置为'x'
    // set it to a failure mode
    memset(to,'y',1000);
    check(valid_copy(to,1000,'y'),"Not initialized right.");
    //验证to字符串的前1000位是否设置为'y'

    // use normal copy to
    rc=normal_copy(from,to,1000);          //normal_copy的返回值代表复制到了多少位
    check(rc==1000,"Normal copy failed:%d",rc);
    check(valid_copy(to,1000,'x'),"Normal copy failed.");

    //reset
    memset(to,'y',1000);

    // duffs version
    rc=duffs_device(from,to,1000);
    check(rc==1000,"Duff's device failed:%d",rc);
    check(valid_copy(to,1000,'x'),"Duff's device failed copy.");

    //reset
    memset(to,'y',1000);

    //my version
    rc=zeds_device(from,to,1000);
    check(rc==1000,"Zed's device failed:%d",rc);
    check(valid_copy(to,1000,'x'),"Zed's device failed copy.");

    return 0;

error:
    return 1;
}