Exercises: Unit 15 — Assembly Language

After this program runs, what number is in the location R?

X     DC    7
Y     DC    -4
Z     DC    5
R     DC    0
      LOAD  X
      ADD   Y
      MULT  Z
      SUB   X
      STORE R
      END

After this program runs, what number is in the location ANS?

P     DC    -17
Q     DC    5
W     DC    3
ANS   DC    0
      LOAD  P
      DIV   Q
      MULT  W
      ADD   =4
      DIV   =2
      STORE ANS
      END

What does this program print?

A     DC    6
B     DC    0
      LOAD  =10
      SUB   A
      STORE B
      MULT  =-5
      ADD   B
      STORE A
      LOAD  A
      DIV   B
      STORE B
      PRINT A
      PRINT B
      END

Write a Python program that does exactly what this assembly program does.

      READ  A
      READ  B
      LOAD  A
      MULT  A
      SUB   B
      DIV   =3
      STORE C
      PRINT C
      LOAD  B
      SUB   A
      DIV   =4
      STORE D
      PRINT D
      END

The input is two whole numbers, A and then B, one per line. Print the two numbers the assembly program prints, one per line, in the same order. Remember that DIV rounds toward zero, which Python's // does not do for negative numbers.

Constraints

• A and B are between −100 and 100.

Sample Input

4
9

Sample Output

2
1

With A = 3 and B = −7, the second number printed is -2: ACC is −10 before DIV =4, and −10 ÷ 4 = −2.5 rounds toward zero.

The input numbers are −7, 0 and 12, in that order. What does this program print?

K     DC    3
LOOP  READ  N
      LOAD  N
      BL    NEG
      BE    ZERO
      MULT  =2
      BU    OUT
NEG   MULT  =-3
      BU    OUT
ZERO  LOAD  =100
OUT   STORE R
      PRINT R
      LOAD  K
      SUB   =1
      STORE K
      BG    LOOP
      END

After this program runs, what number is in the location S?

I     DC    1
S     DC    0
TOP   LOAD  I
      MULT  I
      ADD   S
      STORE S
      LOAD  I
      ADD   =2
      STORE I
      SUB   =9
      BL    TOP
      END

What does this program print?

N     DC    20
LOOP  PRINT N
      LOAD  N
      SUB   =6
      STORE N
      BG    LOOP
      PRINT N
      END

This program reads two whole numbers, X and then Y.

      READ  X
      READ  Y
      LOAD  X
      SUB   Y
      BG    POS
      LOAD  Y
      SUB   X
POS   STORE D
      PRINT D
      END

Which of these describe what the program prints, for every pair of whole numbers X and Y between −1000 and 1000? Choose every one that does.

• A. the larger of X and Y
• B. the distance between X and Y on the number line, |X − Y|
• C. X − Y
• D. the larger of the two numbers X − Y and Y − X
• E. 0 whenever X is less than Y

The input numbers are 8, −15, 3, −7, 0 and 9, in that order. What does this program print?

T     DC    0
C     DC    0
LOOP  READ  X
      LOAD  X
      BE    DONE
      ADD   T
      STORE T
      LOAD  C
      ADD   =1
      STORE C
      BU    LOOP
DONE  LOAD  T
      DIV   C
      STORE A
      PRINT C
      PRINT A
      END

Write a Python program that does exactly what this assembly program does.

S     DC    0
      READ  N
LOOP  LOAD  N
      DIV   =10
      STORE Q
      MULT  =10
      STORE T
      LOAD  N
      SUB   T
      ADD   S
      STORE S
      LOAD  Q
      STORE N
      BG    LOOP
      PRINT S
      END

The input is one whole number N. Print the number the assembly program prints.

Translate the program line by line; do not guess what it "means". Your program must print exactly what the assembly program prints for every allowed input, negative numbers included.

Constraints

• N is between −999,999 and 999,999.

Sample Input

1234

Sample Output

10

For N = 0 the program prints 0.

Write a program that runs a short assembly program that uses only immediate data, and prints ACC after every line.

The first line of input holds a whole number n. Each of the next n lines holds one instruction: an opcode (LOAD, ADD, SUB, MULT or DIV), then one or more spaces, then = and a whole number, such as MULT =-6. There are no labels. ACC starts at 0. After each instruction, print the value of ACC on its own line.

Constraints

• n is between 1 and 20.
• Every number in the input, and every value of ACC, is between −999,999 and 999,999.
• No DIV has =0.

Sample Input

5
LOAD  =7
MULT  =-6
ADD   =3
DIV   =8
SUB   =10

Sample Output

7
-42
-39
-4
-14

-39 DIV 8 is -4, because −39 ÷ 8 = −4.875 rounds toward zero. If the first instruction is DIV =3, the program prints 0, since ACC starts at 0.

What does this program print?

A     DC    84
B     DC    36
C     DC    0
LOOP  LOAD  C
      ADD   =1
      STORE C
      LOAD  A
      SUB   B
      BE    DONE
      BL    SWAP
      STORE A
      BU    LOOP
SWAP  LOAD  B
      SUB   A
      STORE B
      BU    LOOP
DONE  PRINT A
      PRINT C
      END

This program reads one whole number N.

      READ  N
      LOAD  =1
      STORE P
LOOP  LOAD  N
      BE    DONE
      SUB   =1
      STORE N
      LOAD  P
      ADD   P
      STORE P
      BU    LOOP
DONE  PRINT P
      END

Which of these describe what the program prints, for every whole number N from 0 to 19? Choose every one that does.

• A. 2 × N
• B. 2 to the power N (2 multiplied by itself N times; it is 1 when N = 0)
• C. N × N
• D. the number you get by starting at 1 and doubling it N times
• E. N + 1

The input number is 22. What does this program print?

      READ  N
LOOP  LOAD  N
      DIV   =2
      STORE Q
      MULT  =2
      STORE T
      LOAD  N
      SUB   T
      STORE D
      PRINT D
      LOAD  Q
      STORE N
      BG    LOOP
      END

What does this program print?

I     DC    0
S     DC    0
OUTER LOAD  I
      ADD   =1
      STORE I
      SUB   =5
      BE    DONE
      LOAD  I
      STORE J
INNER LOAD  S
      ADD   J
      STORE S
      LOAD  J
      SUB   =1
      STORE J
      BG    INNER
      BU    OUTER
DONE  PRINT S
      END

Write a Python program that does exactly what this assembly program does.

C     DC    0
      READ  N
LOOP  LOAD  N
      SUB   =1
      BE    DONE
      LOAD  N
      DIV   =2
      MULT  =2
      SUB   N
      BE    EVEN
      LOAD  N
      MULT  =3
      ADD   =1
      BU    NEXT
EVEN  LOAD  N
      DIV   =2
NEXT  STORE N
      LOAD  C
      ADD   =1
      STORE C
      BU    LOOP
DONE  PRINT C
      END

The input is one whole number N. Print the number the assembly program prints.

Constraints

• N is between 1 and 1000. (For these inputs, every number the assembly program makes stays below 999,999.)

Sample Input

6

Sample Output

8

For N = 1 the program prints 0: ACC is 0 after SUB =1, so BE DONE jumps straight away.

Extend the interpreter of Lesson 3 so that it runs every ACSL opcode: DC, LOAD, STORE, ADD, SUB, MULT, DIV, BE, BG, BL, BU, READ, PRINT and END, with immediate data =value for LOAD, ADD, SUB, MULT and DIV.

The input is:

1. one line with a whole number n, the number of program lines
2. the n lines of the program, in the column layout of the lesson (words separated by one or more spaces; a line with no label starts with spaces)
3. one line with a whole number m, the number of input numbers
4. m lines, each holding one input number, which the program's READ lines read in order

Run the program from its first line until it reaches END, and print each number a PRINT line prints, on its own line.

The rules are the lesson's:

• ACC starts at 0.
• A line's first word is its label exactly when it is not an opcode.
• Every DC line sets its location before the program starts, even if it comes after END; when the program reaches a DC line, it just moves on.
• A STORE or READ into a label with no DC line makes that location.
• DIV keeps the whole-number part of ACC ÷ LOC, rounding toward zero.

Constraints

• n is between 2 and 60, and m is between 0 and 20.
• Labels start with a letter, go on with letters and digits, and are never opcodes. Each label is on at most one line, and every branch goes to a label that exists.
• A location is always set (by DC, STORE or READ) before it is read, and the program never reads more input numbers than there are.
• Every value stays between −999,999 and 999,999, no DIV divides by zero, and the program reaches END within 10,000 lines run.
• The program prints at least one number.

Sample Input. This is ACSL's N! program with a PRINT added, run with the input 5.

11
      READ  X
      LOAD  X
TOP   SUB   =1
      BE    DONE
      STORE A
      MULT  X
      STORE X
      LOAD  A
      BU    TOP
DONE  PRINT X
      END
1
5

Sample Output

120

What does this program print?

N     DC    9
LIM   DC    30
NEXT  LOAD  N
      ADD   =1
      STORE N
      SUB   LIM
      BG    DONE
      LOAD  =2
      STORE D
TRY   LOAD  D
      MULT  D
      SUB   N
      BG    PRIME
      LOAD  N
      DIV   D
      MULT  D
      SUB   N
      BE    NEXT
      LOAD  D
      ADD   =1
      STORE D
      BU    TRY
PRIME PRINT N
      BU    NEXT
DONE  END