Task: Implementing the toupper() Function

Navigate to tasks/to-upper/support/.

We aim to implement the toupper() function, which converts lowercase letters to uppercase. To do this, start with the to_upper.asm file from the lab exercises archive and complete the body of the toupper() function.

The string used is mystring, and we assume it is a valid string. This string is passed as an argument to the toupper() function when called.

Perform the transformation in place; there is no need for another string.

NOTE_ To convert a lowercase letter to uppercase, you need to subtract 0x20 from its value. This is the difference between lowercase and uppercase letters; for example, a is 0x61, and A is 0x41. You can see this in the ASCII manual page.

To read or write byte by byte, use the byte [reg] construction as seen in the implementation of determining the length of a string in the print_string_length.asm file, where [reg] is the pointer register storing the address of the string at that point.

Stop when you reach the value 0 (NULL byte). For checking, you can use test as seen in the implementation of determining the length of a string in the print-string-length.asm file.

Bonus: toupper() Only for Lowercase Letters

Implement the toupper() function so that the transformation occurs only for lowercase characters, not uppercase letters or other types of characters.

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:

./run_all_tests.sh
test_to_upper_1                  ........................ passed ...  33
test_to_upper_2                  ........................ passed ...  33
test_to_upper_3                  ........................ passed ...  34

Total:                                                           100/100

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