CODEWITHSUNDEEP
mipsqtspimspim
Tragic Coder
Tragic Coder

Reputation: 21

Confused on what this MIPS assignment is asking

I'm not asking for a solution, but i am completely lost on what they are asking for. Can anyone explain to me what they are looking for?

In MIPS/QTSPim, write a subprogram convert_number that converts a string with a C-style integer literal to a value. Implements a main program that prompts the user for two C-style unsigned numbers, calls convert_number to convert the strings to their numerical values, and outputs the sum of the numbers.

convert_number(string, eos)

  • string contains a well-formed C-style literal(number)
  • eos is the end of the string character return value:
  1. C-style integer number:
    • a. Decimal number starts with a digit 1 .. 9, follows by digits 0 .. 9
    • b. Octal number starts with digit 0, follows by digits 0 .. 7
    • c. Hexadecimal number starts with 0x, follows by digits 0 .. 9, a .. f, where a=10, …, f=15
  2. The maximum input will be 10. Use read string syscall to get the input.
  3. No error handlings are required, eg. invalid digit for a base, not a digit, x and a..f are not lowercase
  4. Must use proper subprogram calling convention.

Upvotes: 0

Views: 406

Answers (1)

Rohit D
Rohit D

Reputation: 45

The question seems pretty straightforward - read numbers as a string and convert them into integers and add them up. Your convert_number function would need to handle decimal, octal or hexadecimal numbers. First, you'd read the first character - if it's a digit between 1..9, it's decimal. Otherwise, read the second character and check if it's a 'x'or not to decide between octal and hexadecimal. Save the base of the base of the number in a variable.

To convert the string to decimal:

  1. initialize number = 0.
  2. read one digit of the number. If the digit read is \0, exit. Otherwise, convert the ASCII digit to a number between 0...9.
  3. number *= base
  4. number += digit
  5. go to 2

Once you have this convert_number function in place, all you need to do is use it to write a program along these lines. 

.data
array: .space 1024
.text

main:
    # input & convert string 1
    li $v0, 8
    la $a0, array
    li $v0, 1024
    syscall
    jal convert_number
    move $t0, $v0

    # input & convert string 2
    li $v0, 8
    la $a0, array
    li $v0, 20
    syscall
    jal convert_number
    move $t1, $v0

    # add numbers and print
    addi $a0, $t0, $t1
    li $v0, 1
    syscall

    # exit
    li $v0, 10
    syscall

In MIPS, the convention for writing functions is to put arguments of functions in register $a0 to $a3 (we used $a0 here to send the string address). The values are generally returned using $v0 and $v1 (here $v0 returns the number after converting). There are conventions for what function preserves what registers, but that doesn't really come into play here since we aren't really using nested functions.

Upvotes: 0

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