Use of Stacks Assume a Machine has a single register and six instructions (Probl

Question

Use of Stacks Assume a Machine has a single register and six instructions (Problem 2.3.10 from the LAT text.)

LD A places the operand A in the register

ST A places the contents of the register into the variable A

AD A adds the contents of the variable A to the register

SB A subtracts the contents of the variable A from the register

ML A multiples the contents of the register by the variable A

DV A divides the contents of the register by the variable A

Write a program that accepts a postfix expression containing single letter operands and the operators +, -, *, and / and prints a sequence of instructions to evaluate the expression and leaves the result in the register. Use variables of the form TEMPn as temporary variables. For example, using the postfix expression ABC*+DE-/ should print the following: Note: YOU CANOT USE STACK BUILD IN FUNCTION, define own stack.

LD B

ML C

ST TEMP1

LD A

AD TEMP1

ST TEMP2

LD D

SB E

ST TEMP3

LD TEMP2

DV TEMP3

ST TEMP4

Use the following postfix expressions for input

AB+C-

AB-C+DEF-+$

ABC-/BA-+/

ABCDE-+$*EF*

Explanation / Answer

ST TEMP1 # TEMP1 = REGISTER
LD C # REGISTER = C
AD TEMP1 # REGISTER = REGISTER + TEMP1
ST TEMP2 # TEMP2 = REGISTER
LD E # REGISTER = E
SB F # REGISTER = REGISTER-F
ST TEMP3 # TEMP3 = REGISTER
LD D # REGISTER = D
AD TEMP3 # REGISTER = REGISTER+TEMP3
ST TEMP4 # TEMP4 = REGISTER
LD TEMP2 # REGISTER = TEMP2
DV TEMP4 # REGISTER = REGISTER/TEMP4
ST TEMP5 # TEMP4 = REGISTER

ABC-/BA-+/ CORRECTED BY ABC-/DE-+/ SURPLUS The '/'

LD B # REGISTER = B
SB C # REGISTER = REGISTER-C
ST TEMP1 # TEMP1 = REGISTER
LD A # REGISTER = A
DV TEMP1 # REGISTER = REGISTER/TEMP1
ST TEMP2 # TEMP2 = REGISTER
LD D # REGISTER = D
SB E # REGISTER = REGISTER-E
ST TEMP3 # TEMP3 = REGISTER
LD TEMP2 # REGISTER = TEMP2
AD TEMP3 # REGISTER = REGISTER+TEMP3
ST TEMP4 # TEMP4 = REGISTER

ABCDE-+/*EF* CORRECTED BY '$' POR '/' AND FAILURE '/' ABCDE-+/*EF*/

LD E # REGISTER = E
SB E # REGISTER = REGISTER-E
ST TEMP1 # TEMP1 = REGISTER
LD C # REGISTER = C
AD TEMP1 # REGISTER = REGISTER+TEMP1
ST TEMP2 # TEMP2 = REGISTER
LD B # REGISTER = B
DV TEMP2 # REGISTER = REGISTER/TEMP2
ST TEMP3 # TEMP3 = REGISTER
LD A # REGISTER = A
ML TEMP3 # REGISTER = REGISTER*TEMP3
ST TEMP4 # TEMP4 = REGISTER
LD E # REGISTER = E
ML F # REGISTER = REGISTER*F
ST TEMP5 # TEMP5 = REGISTER
LD TEMP4 # REGISTER = TEMP4
DV TEMP5 # REGISTER = REGISTER/TEMP5
ST TEMP6 # TEMP6 = REGISTER

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