CS 214 Homework 4

CS 214 Homework 4

Introduction
In this assignment, you’ll implement a custom version of malloc, free, and realloc. You should
implement these in mymalloc.c and mymalloc.h. These files should not contain a main function,
so you may want a separate .c file for testing.
You can work in small groups (1 – 3 people). Please include a README file with your code
that contains all partners’ names and netIDs. Only one person from each group should submit the
assignment.
Library functionality
You should implement these functions, described below:
void myinit(int allocAlg);
void* mymalloc(size_t size);
void myfree(void* ptr);
void* myrealloc(void* ptr, size_t size);
void mycleanup();
• myinit(allocAlg)
Create a 1 MB “heap” and perform any other initializations your code needs. You can assume
any application using your library will call this first.
The allocAlg argument describes what algorithm to use to find a free block:
0: first fit
1: next fit
2: best fit
• mymalloc(size)
From the “heap”, allocate a region of at least the requested size and return a pointer to the
beginning of the region. If it cannot be allocated, return NULL.
All returned addresses must be 8-byte aligned. That is, the region you allocate should start
at an address that’s divisible by 8.
If size is 0, mymalloc does nothing and returns NULL.
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• myfree(ptr)
Mark the given region as free and available to be allocated for future requests. It should be
coalesced with adjacent free regions.
You should maintain an explicit free list.
If ptr is NULL, myfree does nothing.
• myrealloc(ptr, size)
Reallocate the region pointed to by ptr to be at least the new given size. If this cannot be
done in-place, a new region should be allocated, the data from the original region should be
copied over, and the old region should be freed.
If the reallocation can’t be done, return NULL.
If ptr is NULL, this is equivalent to mymalloc(size).
If size is 0, this is equivalent to myfree(ptr) and myrealloc returns NULL.
If both ptr is NULL and size is 0, myrealloc does nothing and returns NULL.
• mycleanup()
Free the 1 MB “heap” and perform any other cleanup your code needs. You can assume any
application using your library will call this last.
Your library should support “resetting” everything by calling mycleanup followed by myinit.
Note: outside of myinit and mycleanup, you should not call the standard malloc, calloc,
free, or realloc functions.
Submission
If you develop on your local machine, please be sure to test your code on ilab before submitting.
Please submit the assignment on Canvas as a tar file hw4.tar that, when expanded, produces
a hw4 directory (possibly with additional .c/.h files):
hw4
mymalloc.c
mymalloc.h
README.txt
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