# CS2208b Assignment 3

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## Description

QUESTION 1 (50 marks)
Most goods sold in U.S. and Canadian stores are marked with a Universal Product Code (UPC).
The meanings of the digits underneath the bar code (from left to right) are:
 First digit: type of item,
 First group of five digits: manufacturer,
 Second group of five digits: product, and
 Final digit: check digit, used to help identify an error in the preceding digits.
To compute the check digit,
 Add the first, third, fifth, seventh, ninth, and eleventh digits
 Add the second, fourth, sixth, eighth, and tenth digits
 Multiply the first sum by 3 and add it to the second sum
 The check digit is the digit which, when added to the above sum, produces a sum that is multiple of 10
o Subtract 1 from the total
o Compute the remainder when the adjusted total is divided by 10
o Subtract the remainder from 9
Example for UPC 0 13800 15073 8:
 First sum: 0 + 3 + 0 + 1 + 0 + 3 = 7
 Second sum: 1 + 8 + 0 + 5 + 7 = 21
 Multiplying the first sum by 3 and adding the second yields 42
 Subtracting 1 gives 41
 Remainder upon dividing by 10 is 1
 Remainder is subtracted from 9
 Result is 8
Draw a detailed flowchart and write an ARM assembly program to determine whether a string of 12 ASCII encoded digits
stored in memory is a valid UPC or not. If valid, you should store 1 in r0, if not, you should store 2 in r0. Your code
should be highly optimized, i.e., use as little number of instructions as possible.
You may want to define the 12 digits UPC string as follow:
UPC DCB “013800150738” ;UPC string
To test your program, you can use the following UPCs:
0 60383 75557 7
0 65633 45471 2
You can also get more UPC codes from your own kitchen items.
HINT 1: You can implement the division operation using repeated subtraction.
HINT 2: To calculate 3 × Z, you can do so using only one ADD instruction with LSL#1 shift.
HINT 3: To load a byte to a register, use LDRB not LDR.
QUESTION 2 (50 marks)
Draw a detailed flowchart and write an ARM assembly program to determine whether a string of printable ASCII
encoded characters stored in memory is a palindrome (i.e., the letters in the string are the same from left to right as from
right to left) or not. If palindrome, you should store 1 in r0, if not, you should store 0 in r0. Your code should be highly
optimized, i.e., use as little number of instructions as possible.
Ignore all characters that are not letters. You should also treat capital and small letters the same. For example, “madam”,
“deleveled”, “Noon”, “He lived as a devil, eh?”, and “Was it a car or a cat I saw?” are palindrome strings. However,
A string can have even or odd number of characters and ends with character 0x00 (the ASCII code of the null character).
You may want to define the UPC string as follow:
STRING DCB “He lived as a devil, eh?” ;string
EoS DCB 0x00 ;end of string