chris-gong / mymalloc

CS214 Rutgers Systems Programming Assignment 1: Making a better version of malloc and free

My Malloc

CS214 Rutgers Systems Programming Assignment 1: Making a better version of free and malloc by simulating virtual memory.

Runs on Rutgers iLab machines (Linux x86_64 bit architecture).

To run the program, simply call the make command

make

This will produce not only an object file of mymalloc but also a memgrind executable. To excute the executable, simply call

./memgrind

Note that memgrind.c just tests the malloc and free macros defined in mymalloc. If you wish to implement our malloc and free in your program then replace all instances of memgrind in the Makefile with the name of your program. Also, make sure to include mymalloc.h in your program

#include "mymalloc.h"

Currently, our virtual memory is 5000 bytes but this can be modified by adjusting this line in mymalloc.c.

#define HEAP_SIZE 5000

Right now, the size of the meta blocks are 2 bytes each so this may limit the amount of memory that the simulated heap can hold. If the current struct cannot handle the requested HEAP_SIZE, then consider modifying our struct and bit-masking techniques that allowed us to hold both a size and in_use variable into one short in mymalloc.c

int read_in_use(meta *m) {
  return (m->info >> 15) & 1;
}

void set_in_use(meta *m) {
  m->info |= 1 << 15;
}

void clear_in_use(meta *m) {
  m->info &= ~(1 << 15);
}

unsigned short read_size(meta *m) {
  return m->info & 0x7FFF;
}

void write_size(meta *m, unsigned short new_size) {
  if (new_size > 0x7FFF) return; // TOO BIG
  m->info = (m->info & 0x8000) | (new_size & 0x7FFF);
}

and in mymalloc.h

struct _meta { 
  unsigned short info;
};

For more information on the implementation, check out the readme.pdf file. For more information on some of the test cases in memgrind.c, check out the testcases.txt file.