Programming Exercise $2$ :$-$

COPY A STRING IN REVERSE ORDER

Write a program with a loop $($use the Loop instruction and ECX$)$ and indirect addressing that copies a string from source to target, reversing the character

order in the process. You MUST use the exact data block, memory allocation and initialization, as shown in the followings for testing $-$ for showing that

your code would not over$-$write the original data at the head$(4\text{'}$$$\text{'}$s$)$ middle$(4\text{'}\%\text{'}$s$)$ and tail$(4\text{'}^\text{'}$s$)$:

BYTE $4$ DUP$(\text{'}$$$\text{'})$

source BYTE "This is the source string", $$

BYTE $4$ DUP$(\text{'}\%\text{'})$

target BYTE SIZEOF source DUP $(\text{'}$#$\text{'})$

BYTE $4$ DUP$(\text{'}{?}^{{?}^{?}}\text{'})$

Hint: Should Not copy the null character, $0,$ at the end of the source string to the front of the target string. And, finish writing the target string by

writing the null character, $0,$ to the last byte $-$ replacing the last $\text{'}$#$\text{'}$ there.

In the output of the program, both the source and target$($reversed$)$ strings should be shown, by calling the Irvine peripheral procedure$($s$).$ Use the

following test code to display the Whole Data Bank:

mov edx, OFFSET source$-4$ ; display the $4"$$$"$ and source string

call Writestring

mov al$,$ source$[$SIZEOF source$-1]$ ; if the last char of source is Null, then display it as $\text{'}.\text{'}$

cmp al$,$

jz Disp$\_$Null$\_$char$\_1$

call Writechar

jmp Disp$\_$target$\_$str

Disp$\_$Null$\_$char$\_1$:

mov al$,\text{'}.\text{'}$ ; use $\text{'}.\text{'}$ to represent the Null

call Writechar

Disp$\_$target$\_$str:

mov edx, OFFSET target$-4$ ; display the $4"\%"$ and target string

call Writestring

mov al$,$ target$[$SIZEOF target$-1]$ ; if the last char of target is Null, then display it as $\text{'}.\text{'}$

cmp al$,$

jz Disp$\_$Null$\_$char$\_2$

call Writechar

jmp Disp$\_4\_$hats

Disp$\_$Null$\_$char$\_2$:

mov al$,\text{'}.\text{'}$ ; use $\text{'}.\text{'}$ to represent the Null

call Writechar

Disp$\_4\_$hats:

mov edx, OFFSET target $+$ SIZEOF target ; display the $4"^"$

call Writestring

IMPORTANT: for this exercise, NOT allowable to use any one of these directives: $.$IF$,.$ELSE, $.$ELSEIF, $.$WHILE, $.$REPEAT, etc

Please add a lot of comments to explain step$-$by$-$step