From 18796873e2dbdfff972b3b67cd0f0470cdcd5ac7 Mon Sep 17 00:00:00 2001 From: Matthew Faltys Date: Mon, 17 Feb 2020 14:47:37 +0000 Subject: [PATCH] Add documentation for prj1.asm --- readme.md | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) create mode 100644 readme.md diff --git a/readme.md b/readme.md new file mode 100644 index 0000000..a1303a6 --- /dev/null +++ b/readme.md @@ -0,0 +1,31 @@ +# Project 1 +- You can see this project in action at https://git.unixvoid.com/mfaltys/CSCI-4350 + +The source code for this project is documented line-by-line but I will +go over a broad approach here. + +At the time of writing there are 2 functions: main and lookup: + +## Main +The main function takes some user input (for argument 2, the number to be found) +and stores it into register `$a1` (which is the argument register to send to lookup). +At the same time we set `$a0` and `$a2` which are the base address of array, and the +max index of the array to check (respectively). +When main is returned to after the lookup function it outputs the result +(either the index where the value is found, or `-1`) and prints it to screen. +The last thing main does is make the exit syscall to stop the program. + +## Lookup +The lookup function takes 3 arguments: `$a0`, `$a1`, `$a2` (mentioned above). +The first thing the function does is make a temporary register with a value equalling +one more than the maximum array index we will check +(this way we can determine if the function is out of bounds). +We then check for the out of bounds (oob) case and return a `-1` and jump back to where +we left in main (`$ra`). If we pass the oob check we continue the loop by finding the +current index in the array and comparing it with the value that was passed to us in `$a1`. +If we find the proper value we jump back to `$ra` while passing back the index where +we found it, otherwise we increment the array index counter and loop back to the +start of the lookup function. + +At the bottom of the program is where we store all our data values (hence the `.data` tag). +This is where the array and all our messages are to be used in the program.