Chapter 7

Question 1

Answer 1

Question 2

What does the VM Translator do?

Answer 2

It turns virtual machine code into assembler code.

Question 3

1. At what memory location of the Hack’s RAM is the stack pointer saved?
2. What is the stack’s base address in the Hack computer?

Answer 3

Question 4

What is the translation of the virtual machine command:

“push constant 17”

in Hack assembly?

Answer 4

Question 5

What is the logic for turning the VM code command:

“pop local 2”

int Hack machine code?

Answer 5

Question 6

Answer 6

Question 7

What gets stored in the following memory segments of the Hack’s RAM:

local

argument

this

that

?

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

What are the stages that make the result of a high level Jack program appear on the Hack screen?

Answer 10

Question 11

What is the standard VM mapping on the Hack platform?

Answer 11

Question 12

We want to write “pop local 2” in Hack assembly.

What is the first step?

What Hack code achieves this step?

Answer 12

The first step is to have a variable (D) that will hold the address to which we want to save the poped data.

//D = LCL + 2

@LCL

D=M

@2

D=D+A

Question 13

Answer 13

Question 14

1. What is the minimal number of Hack commands for the VM code: Push constant i
2. What are these commands?

Answer 14

Question 15

1. What is the minimal number of Hack commands for the VM code: Pop temp i
2. What are these commands?

Answer 15

(Base address of temp is 5)

Question 16

1. What is the minimal number of Hack commands for the VM code: Pop (argument/local/this/that) i
2. What are these commands?

Answer 16

Question 17

What will the bottom of the stack be like after:

push 5

push 3

sub

push -3

push 10

sub

Answer 17

2

-13

Question 18

let x be any number.

What will the bottom of the stack look like after:

push x

push -1

and

Answer 18

the last item on the stack will be:

x

This is because an and operation between any number and “111…111” (= the binary representation of -1) gives back the same number.

Question 19

push 101101

push x

or

What value of x will give us the first number pushed?

Answer 19

00000

Question 20

Let x be any value.

What will the bottom of the stack look like after?

push 0000

push 1111

push x

and

or

Answer 20

x