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)
{
	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;

	//Init the two vectors and check them
	memset(from,'x',1000);
	memset(to,'y',1000);
	check(valid_copy(from,1000,'x'),"Not initialized right"); 
	check(valid_copy(to,1000,'y')  ,"Not initialized right"); 

	//Copy with for loops
	rc = normal_copy(from,to,1000);
    check(rc == 1000, "Normal copy failed: %d", rc);
    check(valid_copy(to, 1000, 'x'), "Normal copy failed.");

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