Task: Sum of Elements in an Array

Introduction

You will solve this exercise starting from the sum_array.asm file located in the tasks/sum-array/support directory.

In the sum_array.asm file, the sum of elements in arrays of different data types is calculated.

Follow the code, observe the constructions and registers specific for working with different data types in 64-bit mode. Run the code.

IMPORTANT: Proceed to the next step only after thoroughly understanding what the code does. It will be difficult for you to complete the following exercises if you have difficulty understanding the current exercise.

Working with Arrays of Different Sizes

In the TODO section of the sum-array.asm file, complete the code to calculate the sum of:

  1. word_array (16-bit elements)
  2. dword_array (32-bit elements)
  3. qword_array (64-bit elements)

TIP: When calculating the address of an element in an array, you will use a construction like:

base + size * index

In the construction above:

  • base is the address of the array (i.e., word_array, dword_array etc.)
  • size is the length of the array element (i.e., 2 for a word array (16 bits, 2 bytes) and 4 for a dword array (32 bits, 4 bytes))
  • index is the current index within the array

NOTE: The expected sums for each array are:

  • sum(byte_array): 575
  • sum(word_array): 65799
  • sum(dword_array): 140975
  • sum(qword_array): 49782475293

128-bit Addition Exercise

The final part of this lab requires you to implement a 128-bit addition operation.

You need to add three very large 64-bit values stored in the big_qword_array:

big_qword_array dq 9223372036854775800, 8223372036854775800, 7223372036854775800

NOTE: When adding these values, the sum will exceed the capacity of a single 64-bit register (rax). You will also have to track and handle the carry bits.

NOTE: The expected result of adding these three values is: 0x1565ddbe509d3ffe8.

Testing

To test the implementation, enter the tests/ directory and run:

make check

In case of a correct solution, you will get an output such as:

word_sum_test                    ........................ passed ...  20
dword_sum_test                   ........................ passed ...  20
qword_sum_test                   ........................ passed ...  30
big_sum_test                     ........................ passed ...  30

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Total:                                                           100/100

Additional Resources

If you’re having difficulties solving this exercise, go through this reading material.