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 */
    "C-MB",
    /* First member's full name */
    "Christopher Beard",
    /* First member's email address */
    "cbeard1@binghamton.edu",
    /* Second member's full name (leave blank if none) */
    "Christopher Maltzan",
    /* Second member's email address (leave blank if none) */
    "cmaltza1@binghamton.edu"
};

/* 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)))

/* 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)))

int mm_init(void);
static void *extend_heap(size_t words);
void *mm_malloc(size_t size);
void mm_free(void *ptr);
void *mm_realloc(void *ptr, size_t size);
static void *coalesce(void *bp);
static void *find_fit(size_t asize);
static void place(void *bp, size_t asize);

static char *heap_listp;

/* 
 * mm_init - initialize the malloc package.
 */
int mm_init(void)
{
    /* Create initial empty heap */
    if ((heap_listp = mem_sbrk(4 * WSIZE)) == (void *) - 1) {
        return -1;
    }
        
    PUT(heap_listp, 0);
    PUT(heap_listp + (1 * WSIZE), PACK(DSIZE, 1));
    PUT(heap_listp + (2 * WSIZE), PACK(DSIZE, 1));
    PUT(heap_listp + (3 * WSIZE), PACK(DSIZE, 1));
    heap_listp += (2 * WSIZE);

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

/*
 * extend_heap - extends the heap by creating new free block at the of the list
 */
static void *extend_heap(size_t words)
{
    char *bp;
    size_t size;

    /* Allocate an even number of words for alignment puruposes */
    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);
}

/* 
 * mm_malloc - Allocate a block by incrementing the brk pointer. May extend heap if needed.
 *     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 if it no fit */
    char *bp;

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

	/* Allignment rules force 16 bytes to be allocated for small data */
    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);
		
		//--------------------------
		char *bp_prev = PREV_BLKP(bp);
		char *bp_next = NEXT_BLKP(bp);
		while (GET_ALLOC(bp_next) && (GET(bp_next) != NULL)) {
			*bp_next = NEXT_BLKP(bp_next);
		}
		


		//--------------------------

        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;
}

/*
 * mm_free - Frees the block at the given pointer.
 */
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);
}

/*
 * coalesce - Merges free blocks with free neighboring blocks if possible
 */
static void *coalesce(void *bp)
{
    /* Check the next/previous blocks' allocation status */
    size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
    size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
    
    /* Get the size of the block */
    size_t size = GET_SIZE(HDRP(bp));

    /* Next/Previous blocks are allocated */
    if (prev_alloc && next_alloc) {                 /* Case 1 */
        return bp;
    }

    /* Next block free, previous allocated */
    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));
    }

    /* Previous block free, next allocated */
    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);
    }

    /* Both next and previous block are free */
    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(PREV_BLKP(bp)), PACK(size, 0));
        bp = PREV_BLKP(bp);
    }

    return bp;
}

/*
 * find_fit - Search for first blocks with enough space in heap for block to be placed
 */
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 */
}

/*
 * place - Place block of size asize in the heap
 */
static void place(void *bp, size_t asize)
{
	/* csize = size of free block */
    size_t csize = GET_SIZE(HDRP(bp));

	/* If difference between free block and inserted data unit can be used for a full block */
    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));
    }
	/* Difference is either 0 or alignment rules prevent another block from being created */
    else {
        PUT(HDRP(bp), PACK(csize, 1));
        PUT(FTRP(bp), PACK(csize, 1));
    }
}

/*NEXT_BLKP(bp)
 * mm_realloc - Implemented simply in terms of mm_malloc and mm_free
 */
void *mm_realloc(void *ptr, size_t size)
{

/*    void *p;*/
/*    */
/*    if (NULL == ptr) {*/
/*        return malloc(size);*/
/*    } else if (0 == size) {*/
/*        free(ptr);*/
/*        return NULL;*/
/*    } else {*/
/*        p = malloc(size);*/
/*        memcpy(p, ptr, size);*/
/*        free(ptr);*/
/*        return p;*/
/*    }*/


     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;
}