malloc-lab/mm.c

/*
 * mm-naive.c - The fastest, least memory-efficient malloc package.
 *
 * In this naive approach, a block is allocated by simply incrementing
 * the brk pointer.  A block is pure payload. There are no headers or
 * footers.  Blocks are never coalesced or reused. Realloc is
 * implemented directly using mm_malloc and mm_free.
 *
 * NOTE TO STUDENTS: Replace this header comment with your own header
 * comment that gives a high level description of your solution.
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>

#include "mm.h"
#include "memlib.h"

/*********************************************************
 * NOTE TO STUDENTS: Before you do anything else, please
 * provide your team information in the following struct.
 ********************************************************/
team_t team = {
  /* Team name */
  "anna.schlittenhardt@stud.uni-due.de+tuan-dat.tran@stud.uni-due.de",
  /* First member's full name */
  "Anna Schlittenhardt",
  /* First member's email address */
  "anna.schlittenhardt@stud.uni-due.de",
  /* Second member's full name (leave blank if none) */
  "Tuan-Dat Tran",
  /* Second member's email address (leave blank if none) */
  "tuan-dat.tran@stud.uni-due.de"
};

/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8

/* rounds up to the nearest multiple of ALIGNMENT */
#define ALIGN(size) (((size) + (ALIGNMENT-1)) & ~0x7)

#define SIZE_T_SIZE (ALIGN(sizeof(size_t)))

/* Page 830, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/* Basic constants and macros */
#define WSIZE 4 /* Word and header/footer size (bytes) */
#define DSIZE 8 /* Double word size (bytes) */
#define CHUNKSIZE (1<<12) /* Extend heap by this amount (bytes) */

#define MAX(x, y) ((x) > (y)? (x) : (y))

/* Pack a size and allocated bit into a word */
#define PACK(size, alloc) ((size) | (alloc))

/* Read and write a word at address p */
#define GET(p) (*(unsigned int *)(p))
#define PUT(p, val) (*(unsigned int *)(p) = (val))

/* Read the size and allocated fields from address p */
#define GET_SIZE(p) (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)

/* Given block ptr bp, compute address of its header and footer */
#define HDRP(bp) ((char *)(bp) - WSIZE)
#define FTRP(bp) ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)

/* Given block ptr bp, compute address of next and previous blocks */
#define NEXT_BLKP(bp) ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE)))
#define PREV_BLKP(bp) ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE)))

static char *heap_listp;

/* Page 856-858, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
static void place(void *bp, size_t asize)
{
  size_t csize = GET_SIZE(HDRP(bp));
  if ((csize - asize) >= (2*DSIZE)) {
    PUT(HDRP(bp), PACK(asize, 1));
    PUT(FTRP(bp), PACK(asize, 1));
    bp = NEXT_BLKP(bp);
    PUT(HDRP(bp), PACK(csize-asize, 0));
    PUT(FTRP(bp), PACK(csize-asize, 0));
  }
  else {
    PUT(HDRP(bp), PACK(csize, 1));
    PUT(FTRP(bp), PACK(csize, 1));
  }
}

/* Page 856, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
static void *find_fit(size_t asize)
{
  /* First fit search */
  void *bp;

  for (bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp)) {
    if (!GET_ALLOC(HDRP(bp)) && (asize <= GET_SIZE(HDRP(bp)))) {
      return bp;
    }
  }
  return NULL; /* No fit */
}

/* Page 833, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
static void *coalesce(void *bp) {
  size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
  size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
  size_t size = GET_SIZE(HDRP(bp));

  if (prev_alloc && next_alloc) {                /* Case 1 */
    return bp;
  } else if (prev_alloc && !next_alloc) {        /* Case 2 */
    size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
    PUT(HDRP(bp),PACK(size,0));
    PUT(FTRP(bp),PACK(size,0));
  } else if (!prev_alloc && next_alloc) {        /* Case 3 */
    size += GET_SIZE(HDRP(PREV_BLKP(bp)));
    PUT(FTRP(bp), PACK(size, 0));
    PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
    bp = PREV_BLKP(bp);
  } else {                                       /* Case 4 */
    size += GET_SIZE(HDRP(PREV_BLKP(bp))) +
      GET_SIZE(FTRP(NEXT_BLKP(bp)));
    PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
    PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
    bp = PREV_BLKP(bp);
  }
  return bp;
}

/* Page 831, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
static void *extend_heap(size_t words)
{
  char *bp;
  size_t size;

  /* Allocate an even number of words to maintain alignment */
  size = (words % 2) ? (words+1) * WSIZE : words * WSIZE;
  if ((long)(bp = mem_sbrk(size)) == -1)
    return NULL;

  /* Initialize free block header/footer and the epilogue header */
  PUT(HDRP(bp), PACK(size,0)); /* Free block header */
  PUT(FTRP(bp), PACK(size,0)); /* Free block footer */
  PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1)); /* New epilogue header */

  /* Coalesce if the previous block was free */
  return coalesce(bp);
}


/* Page 831, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_init - initialize the malloc package.
 */
int mm_init(void)
{
  /* Create the initial empty heap */
  if ((heap_listp = mem_sbrk(4*WSIZE)) == (void *)-1)
    return -1;
  PUT(heap_listp, 0); /* Alignment padding */
  PUT(heap_listp + (1*WSIZE), PACK(DSIZE, 1)); /* Prologue header */
  PUT(heap_listp + (2*WSIZE), PACK(DSIZE, 1)); /* Prologue footer */
  PUT(heap_listp + (3*WSIZE), PACK(0, 1));   /* Epilogue header */
  heap_listp += (2*WSIZE);

  /* Extend the empty heap with a free block of CHUNKSIZE bytes */
  if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
    return -1;
  return 0;
}

/* Page 834, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_malloc - Allocate a block by incrementing the brk pointer.
 *     Always allocate a block whose size is a multiple of the alignment.
 */
void *mm_malloc(size_t size)
{
  size_t asize;
  /* Adjusted block size */
  size_t extendsize; /* Amount to extend heap if no fit */
  char *bp;

  /* Ignore spurious requests */
  if (size == 0)
    return NULL;

  /* Adjust block size to include overhead and alignment reqs. */
  if (size <= DSIZE)
    asize = 2*DSIZE;
  else
    asize = DSIZE * ((size + (DSIZE) + (DSIZE-1)) / DSIZE);
  /* Search the free list for a fit */
  if ((bp = find_fit(asize)) != NULL) {
    place(bp, asize);
    return bp;
  }

  /* No fit found. Get more memory and place the block */
  extendsize = MAX(asize,CHUNKSIZE);
  if ((bp = extend_heap(extendsize/WSIZE)) == NULL)
    return NULL;
  place(bp, asize);
  return bp;
}

/* Page 833, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_free - Freeing a block does nothing.
 */
void mm_free(void *ptr)
{
  size_t size= GET_SIZE(HDRP(ptr));
  PUT(HDRP(ptr), PACK(size, 0));
  PUT(FTRP(ptr), PACK(size, 0));
  coalesce(ptr);
}

/*
 * mm_realloc - Implemented simply in terms of mm_malloc and mm_free
 */
void *mm_realloc(void *ptr, size_t size)
{
  /*
   * ATTENTION: You do not need to implement realloc for this assignment
   */
  void *oldptr = ptr;
  void *newptr;
  size_t copySize;

  newptr = mm_malloc(size);
  if (newptr == NULL)
    return NULL;
  copySize = *(size_t *)((char *)oldptr - SIZE_T_SIZE);
  if (size < copySize)
    copySize = size;
  memcpy(newptr, oldptr, copySize);
  mm_free(oldptr);
  return newptr;
}

////////////////////////////////////////////////////////////////
/// Helper Functions
////////////////////////////////////////////////////////////////