Project: "Alice$$s Reversal Through the Looking Buffer"

Scenario: Alice finds herself once again in Wonderland, tasked by the mysterious Caterpillar with a peculiar

request: to reverse a string using two enchanted buffers, Tweedledum and Tweedledee. However, the reversal

must be done with finesse$$no condiConal jumps, only a single loop, and indirect addressing! With the help of

magical scrolls $($BYTE arrays$)$ and some assembly wizardry, Alice is ready for the challenge.

The Task:

You, as Alice$$s assistant, will write a MASM program that:

$1.$ Reads a string from the Caterpillar $($user input$)$ into the Tweedledee buffer using the ReadString

procedure.

$2.$ Reverses the string from Tweedledee into the Tweedledum buffer using indirect addressing in a single

loop, without using condiConal or uncondiConal jumps.

$3.$ Displays both the original and reversed strings to the Caterpillar using the WriteString procedure.

Rules of Wonderland $($InstrucHons$)$:

$1.$ You MUST use OFFSET to manage the buffers$$ memory addresses$$no LEA instrucCons allowed!

$2.$ You MUST use the LOOP instrucCon, and no condiConal or uncondiConal jumps $($CMP$,$ JMP$,$ etc.$)$ are

permiWed.

$3.$ The code MUST be formaWed correctly so even the Mad HaWer can read it clearly before the

Jabberwocky arrives.

$4.$ File Naming: Name the source code file in the format eof$221$proj$03$USERNAME.asm $($replace

USERNAME with your username$).$

$5.$ CollaboraHon: You may assist each other, but no plagiarism$$each soluCon must be your own!

Detailed DirecHons:

$1.$ Buffer Setup:

o Define two byte arrays of size $256$: Tweedledee $($which will hold the input string$)$ and

Tweedledum $($which will hold the reversed string$).$

o Ensure Tweedledum is empty at the start.

$2.$ Procedures to Use:

o ReadString: Read the string from the user into Tweedledee. The user can input up to $255$

characters $($the $256$th byte is reserved for the null terminator$).$

o WriteString: Display the contents of both Tweedledee $($original$)$ and Tweedledum $($reversed$).$

$3.$ Using Indirect Addressing with ESI and EDI:

o Set up ESI to point to the last character of the string in Tweedledee.

o Set up EDI to point to the first posiCon of Tweedledum.

o In each iteraCon of the LOOP:

$$ Move the character from $[$ESI$]($Tweedledee$)$ to the AL register.

$$ Move the character from AL into $[$EDI$]($Tweedledum$).$

$$ Decrement ESI $($move backward through Tweedledee$).$

$$ Increment EDI $($move forward through Tweedledum$).$

$4.$ Using the LOOP InstrucHon:

o Use a counter to control the number of iteraCons based on the length of the input string.

o The LOOP instrucCon will automaCcally decrement the counter and conCnue the loop unCl it

reaches zero.

$5.$ Null$-$Terminate the Reversed String:

o Aber the loop, place a null terminator $(0)$ at the end of Tweedledum.

$6.$ Display the Results:

o Use WriteString to print both the original string $($from Tweedledee$)$ and the reversed string

$($from Tweedledum$).$

Reminders:

$$ OFFSET, not LEA: Use the OFFSET direcCve to handle the memory addresses of Tweedledee and

Tweedledum.

$$ LOOP: The loop must be controlled solely by the LOOP instrucCon$$no condiConal or uncondiConal

jumps.

$$ File Naming: The source code file must be named in the format eof$221$proj$03$USERNAME.asm $($replace

USERNAME with your username$).$

$$ CollaboraHon: Help each other, but make sure the work is your own$$plagiarism is not permiWed!

Final Call:

The Caterpillar awaits your help, Alice! By using indirect addressing and a single LOOP, reverse the string and

display it before the Jabberwocky arrives!