Malloc And Free Library (LowRes NX)

SP4CEBAR 2024-11-23 17:25 (Edited)

This library includes subprograms to allow NX's RAM to be utilized more effectively using malloc and free just like in the C programming language.

how to use

Storing 5 bytes:
1. Call the malloc subprogram with the parameter 5, malloc will return a memory address and an error code.
2. If the error code is zero you can write the five bytes consecutively starting at the given memory address, make sure to fill all of this memory because it may still contain data from a previous task, also make sure to never read to or write from unallocated space.
3. Store the memory address and the size somewhere safe because you will need this to access the data.
4. Whenever you are done with the memory location you can call the free subprogram with the memory address, if the returned error code is zero then this memory location has been "deleted" so that this space can be reused by other malloc calls.

Some data structures have their roots in malloc, so we can now make structures like a linked list more easily.

Here are the main functions

MAL_MALLOC( R_CHUNK_ADDRESS, REQUESTED_CHUNK_SIZE, R_ERROR_CODE )
MAL_FREE( CHUNK_ADDRESS, R_ERROR_CODE )
MAL_INIT_HEAP( HEAP_ADDRESS, HEAP_SIZE )
MAL_LEAK_FINDER

MAL_INIT_HEAP is used to set the heap location and size. It also generates a chunk to fill the heap with "unallocated space". The heap is the memory space in which malloc and free will work. Calling this subprogram is part of the setup subroutine.

MAL_LEAK_FINDER will trace all allocated chunks, it is a bad practice to leave allocated chunks when a program exits, this would cause a memory leak in other programming languages.

Technical details:

each chunk is prefixed by a 2-byte header
each header is read from POKEL
- the abs() represents the size of the chunk
- the sgn() represents the is_allocated flag
- dedicated subprograms exist to set and get the header information