mm-implicit.c

/*
 * mm-implicit.c
 *
 * Provides an implicit list implementation of malloc as per the text book
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>

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

team_t team = {
    /* Team name */
    "amm668",
    /* First member's full name */
    "Alexander Madjar",
    /* First member's email address */
    "AlexanderMadjar2012@u.northwestern.edu",
    /* Second member's full name (leave blank if none) */
    "",
    /* Second member's email address (leave blank if none) */
    ""
};

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

/* rounds up to the nearest multiple of ALIGNMENT 
    NOTE: ALIGNMENT must be a multiple of two
 */
#define ALIGN(size) (((size) + (ALIGNMENT-1)) & ~(ALIGNMENT-1))

/* 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)

#define HDRP(bp) ((char *)(bp) - WSIZE)
#define FTRP(bp) ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)
#define NEXT_BLKP(bp) ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE)))
#define PREV_BLKP(bp) ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE)))

//Global
char* heap_listp;

static inline void *extend_heap(size_t words);
static inline void *coalesce(void *bp);
static inline void place(void* bp, size_t asize);
static inline void *find_fit(size_t asize);

/* 
 * 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;
}


static inline 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);
}

void mm_free(void *bp){
  size_t size = GET_SIZE(HDRP(bp));
  PUT(HDRP(bp),PACK(size, 0));
  PUT(FTRP(bp),PACK(size, 0));
  coalesce(bp);
}

static inline 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) {
    return bp;
  }
  else if (prev_alloc && !next_alloc) {
    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) {
    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 {
    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; 
}

void *mm_malloc(size_t size)
{
  size_t asize;
  size_t extendsize;
  char *bp;
  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;
}


static inline void *find_fit(size_t asize)
{
  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;
}

static inline 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));
  }

}







/*
 * mm_realloc - Implemented simply in terms of mm_malloc and mm_free
 * HINT: this will always work, so save making this more efficient for later
 */
void *mm_realloc(void *ptr, size_t size)
{
    void *oldptr = ptr;
    void *newptr;
    size_t copySize;
    
    newptr = mm_malloc(size);
    if (newptr == NULL)
      return NULL;
    copySize = *(size_t *)((char *)oldptr - 8);
    if (size < copySize)
      copySize = size;
    memcpy(newptr, oldptr, copySize);
    mm_free(oldptr);
    return newptr;
}