Brainfry

The objective of this assignment is to put into practice the learnt assembly concepts and problemsolving

skills in order to decompose and implement a complex task $($by the standards of assembly

programming$)$ while testing your ingenuity. You will be implementing a compiler for an esoteric

programming language called Brainfry $($reminiscent of a similar, not$-$so$-$appropriately$-$named

language$).$

Description

Brainfry is an esoteric programming language that uses a small set of simple commands to manipulate

a virtual $$tape$$ of memory cells. The tape is represented as an array of memory cells, each of which

can hold a single data byte. The commands in Brainfry manipulate the tape by moving the $$tape

head$($which is a pointer to the current memory cell$)$ left or right, incrementing or decrementing the

value of the current memory cell, and accepting or outputting the value of the current memory cell.

The commands in Brainfry are:

$>$: move the tape head to the right.

$<$: move the tape head to the left.

$+$: increment the value of the current memory cell.

$-$: decrement the value of the current memory cell.

$.$: output the value of the current memory cell as an ASCII character.

$,$: input a value from the user and store it in the current memory cell.

$[$: if the value of the current memory cell is $0,$ jump to the corresponding $]$ command.

$]$: if the value of the current memory cell is not $0,$ jump to the corresponding $[$ command.

All other input characters are ignored. The program written in Brainfry is executed by an interpreter

that reads the commands one by one and executes them to manipulate the $($contents on the$)$ tape.

Example

$[$

This loop is an "initial comment loop", a simple way of adding a comment

to a BF program such that you don$$t have to worry about any command

characters. Any $".",",","+","-","<"$ and $">"$ characters are simply

ignored, the $"["$ and $"]"$ characters just have to be balanced. This

loop and the commands it contains are ignored because the current cell

defaults to a value of $0$; the $0$ value causes this loop to be skipped.

$]$

$[$ This is a comment $]$

$>++$

$[$

This is also a comment but

$-$

The instruction above got executed

$]$

~

You can now look at the second memory register, and you should see the value $0($x$0000)$ in there.

Constraints and simplifications

Usually, Brainfry$$s tape is $65$k $(65,000)$ elements long. However, to accommodate the limitations of

LC$3,$ your tape does not have to be longer than $5$k$,$ and it$$s guaranteed that the programs that we

submit to your compiler will not go into negative tape indexes.

Additionally, a normal Brainfry program would stop when it reads the EOF $($End of File$)$ symbol,

however, to simplify this, we have decided to add a ~ character to symbolise $$End of Program$.$

What follows after this symbol is the input to the Brainfry program. Note that all programs are

built to read deterministic code.

Act as all memory has been set to $0$; you do not need to preset it$.$

Write the code for it in LC$3$ assembly