malloclab/mm.c

#include <string.h>
#include <stdlib.h>
#include <assert.h>

#include "mm.h"
#include "memlib.h"
#include "list.h"
#include "config.h"


struct boundary_tag {
    int inuse:1;
    int size:31;
};

/* FENCE is used for heap prologue/epilogue. */
const struct boundary_tag FENCE = {
    .inuse = 1,
    .size = 0
};

struct block {
    struct boundary_tag header;
    char payload[0];
    struct list_elem elem;
};

static struct block *heap_listp = 0;

/* Basic constants and macros */
#define WSIZE       sizeof(struct boundary_tag)  /* Word and header/footer size (bytes) */
#define DSIZE       2*WSIZE
#define MIN_BLOCK_SIZE_WORDS 8  /* Minimum block size in words */
#define CHUNKSIZE  (1<<10)  /* Extend heap by this amount (words) */

#define NUM_LISTS 8 /* Number of free lists */

static inline size_t max(size_t x, size_t y) {
    return x > y ? x : y;
}



static size_t align(size_t size) {
  return (size + ALIGNMENT - 1) & ~(ALIGNMENT - 1);
}


static struct list free_lists[NUM_LISTS];
static size_t list_sizes[NUM_LISTS];

/* Function prototypes for internal helper routines */
static struct block *extend_heap(size_t words, int realloc);
static void place(struct block *blck, size_t asize);
static struct list* find_list(size_t size);
static struct block *find_fit(size_t num_words);
//~ static void coalesce_free_lists();
static struct block *coalesce(struct block *bp);

/* Given a block, obtain previous's block footer.
   Works for left-most block also. */
static struct boundary_tag * prev_blk_footer(struct block *blk) {
    return &blk->header - 1;
}

/* Return if block is free */
static bool blk_free(struct block *blk) { 
    return !blk->header.inuse; 
}

/* Return size of block is free */
static size_t blk_size(struct block *blk) {
    return blk->header.size;
}

/* Given a block, obtain pointer to previous block.
   Not meaningful for left-most block. */
static struct block *prev_blk(struct block *blk) {
    struct boundary_tag *prevfooter = prev_blk_footer(blk);
    assert(prevfooter->size != 0);
    return (struct block *)((void *)blk - WSIZE * prevfooter->size);
}

/* Given a block, obtain pointer to next block.
   Not meaningful for right-most block. */
static struct block *next_blk(struct block *blk) {
    assert(blk_size(blk) != 0);
    return (struct block *)((void *)blk + WSIZE * blk->header.size);
}

/* Given a block, obtain its footer boundary tag */
static struct boundary_tag * get_footer(struct block *blk) {
    return ((void *)blk + WSIZE * blk->header.size)
                   - sizeof(struct boundary_tag);
}


/* Set a block's size and inuse bit in header and footer */
static void set_header_and_footer(struct block *blk, int size, int inuse) {
    blk->header.inuse = inuse;
    blk->header.size = size;
    * get_footer(blk) = blk->header;    /* Copy header to footer */
}



/* Mark a block as used and set its size. */
static void set_block_used(struct block *blk, int size) {
    set_header_and_footer(blk, size, 1);
}


/* Mark a block as free and set its size. */
static void set_block_free(struct block *blk, int size) {
    set_header_and_footer(blk, size, 0);
}

int mm_init(void) 
{
    assert (offsetof(struct block, payload) == 4);
    assert (sizeof(struct boundary_tag) == 4);

    /* Create the initial empty heap */
    struct boundary_tag * initial = mem_sbrk(4 * sizeof(struct boundary_tag));
    if (initial == NULL)
        return -1;

    /* We use a slightly different strategy than suggested in the book.
     * Rather than placing a min-sized prologue block at the beginning
     * of the heap, we simply place two fences.
     * The consequence is that coalesce() must call prev_blk_footer()
     * and not prev_blk() because prev_blk() cannot be called on the
     * left-most block.
     */
    initial[2] = FENCE;                     /* Prologue footer */
    heap_listp = (struct block *)&initial[3];
    initial[3] = FENCE;                     /* Epilogue header */
    
    for (int i = 0; i < NUM_LISTS; i++) {
		struct list current_list;
		list_init(&current_list);
		free_lists[i] = current_list;
	}
	
	for (int i = 0; i < NUM_LISTS; i++)
		list_sizes[i] = MIN_BLOCK_SIZE_WORDS * (i + 1);

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

/*
* The mm malloc routine returns a pointer to an allocated block payload of at
* least size bytes. The entire allocated block should lie within the heap region and should
* not overlap with any other allocated chunk.
*/
void *mm_malloc(size_t size) {
    struct block *blck;

    if (size == 0) {
        return NULL;
    }

    size_t words = max(MIN_BLOCK_SIZE_WORDS, align(size + DSIZE) / WSIZE);

    /* Find fit for size */
    if ((blck = find_fit(words)) != NULL) {
        place(blck, words);
        return blck->payload;
    }
    
    //~ coalesce_free_lists();
    //~ if ((blck = find_fit(words)) != NULL) {
        //~ place(blck, words);
        //~ return blck->payload;
    //~ }

    if ((blck = extend_heap(words, 0)) == NULL){
        return NULL;
    }
    place(blck, words);
    return blck->payload;
}

void mm_free(void *bp)
{
    assert (heap_listp != 0);       // assert that mm_init was called
    if (bp == 0) 
        return;

    /* Find block from user pointer */
    struct block *blk = bp - offsetof(struct block, payload);
    size_t size = blk_size(blk);

    set_block_free(blk, size);
    
    list_push_front(find_list(size), &blk->elem);
    
    coalesce(blk);
}

//~ static void coalesce_free_lists()
//~ {
	//~ for (int i = 0; i < NUM_LISTS; i++) {
		//~ struct list* current_list = &free_lists[i];
		//~ for (struct list_elem* e = list_begin(current_list); e != list_back(current_list); e = list_next(e)) {
			//~ struct block* bp = list_entry(e, struct block, elem);
			//~ coalesce(bp);
		//~ }
	//~ }
//~ }

void *mm_realloc(void *ptr, size_t size) {
    void *new_ptr = NULL;

    if (ptr == NULL) {
        return mm_malloc(size);
    }

    if (size == 0) {
        mm_free(ptr);
        return NULL;
    }

    struct block *oldblock = ptr - offsetof(struct block, payload);
    size_t oldwords = blk_size(oldblock);
    size_t oldsize = oldwords * WSIZE;
    
    if (!(new_ptr = mm_malloc(size))) {
        return NULL;
    }
    if (size < oldsize) {
        oldsize = size;
    }
    memcpy(new_ptr, ptr, oldsize);
    mm_free(ptr);

    return new_ptr;

}

static struct block *coalesce(struct block *bp) 
{
    bool prev_alloc = prev_blk_footer(bp)->inuse;   /* is previous block allocated? */
    bool next_alloc = ! blk_free(next_blk(bp));     /* is next block allocated? */
    size_t size = blk_size(bp);

    if (prev_alloc && next_alloc) {            /* Case 1 */
        // both are allocated, nothing to coalesce
        return bp;
    }

    else if (prev_alloc && !next_alloc) {      /* Case 2 */
        // combine this block and next block by extending it
        list_remove(&bp->elem);
        set_block_free(bp, size + blk_size(next_blk(bp)));
        list_remove(&next_blk(bp)->elem);
        list_push_front(find_list(size + blk_size(next_blk(bp))), &bp->elem);
    }

    else if (!prev_alloc && next_alloc) {      /* Case 3 */
        // combine previous and this block by extending previous
        list_remove(&bp->elem);
        bp = prev_blk(bp);
        set_block_free(bp, size + blk_size(bp));
        list_remove(&bp->elem);
        list_push_front(find_list(size + blk_size(next_blk(bp))), &bp->elem);
        
    }

    else {                                     /* Case 4 */
        // combine all previous, this, and next block into one
        list_remove(&bp->elem);
        set_block_free(prev_blk(bp), 
                        size + blk_size(next_blk(bp)) + blk_size(prev_blk(bp)));
        bp = prev_blk(bp);
        list_remove(&bp->elem);
        list_remove(&next_blk(bp)->elem);
        list_push_front(find_list(size + blk_size(next_blk(bp))), &bp->elem);
    }
    return bp;
}

/*
 * Extend heap with free block and return its block pointer
 * Does not add new block to free list if called by realloc
 */
static struct block *extend_heap(size_t words, int realloc)
{
    void *blck = mem_sbrk(words * WSIZE);

    if (blck == NULL)
        return NULL;

    /* Initialize free block header, footer and epilogue header. */
    struct block * blk = blck - sizeof(FENCE);
    set_block_free(blk, words);
    next_blk(blk)->header = FENCE;
    
    if (realloc) {
        return blk;
    }
    list_push_front(find_list(words), &blk->elem);

    
    return coalesce(blk);
   
}


/*
 * Allocate block of memory at address blck
 */
static void place(struct block *blck, size_t asize) {
    size_t csize = blk_size(blck);

    /* Remove block from free list */
    list_remove(&blck->elem);

    size_t remaining_size = csize - asize;
    if (remaining_size >= MIN_BLOCK_SIZE_WORDS) {
        set_block_used(blck, asize);
        blck = next_blk(blck);
        set_block_free(blck, remaining_size);

        /* Add remaining free block back into list */
        list_push_front(find_list(remaining_size), &blck->elem);
    }
    else {
        set_block_used(blck, csize);
    }
}

/**
 * Find free list with blocks of given size
 */
static struct list* find_list(size_t n_words) {
    
    for (int i = 0; i < NUM_LISTS; i++) {
        if ((n_words < list_sizes[i]) || (i == (NUM_LISTS - 1))) {
            if (list_empty(&free_lists[i])) {
                continue;
            }
            return &free_lists[i];
        }
    }
    return NULL;
}

/*
 * Find a fit for a block with num_words
 */
static struct block *find_fit(size_t num_words)
{
    struct list* free_list = find_list(num_words);
    
    if (free_list == NULL) {
        return NULL;
    }

    /* Search for block from selected free list*/
    for (struct list_elem* e = list_back(free_list); e != list_head(free_list); e = list_prev(e)) {
        struct block* bp = list_entry(e, struct block, elem);
        if (num_words <= blk_size(bp)) {
            return bp;
        }
    }
    return NULL;
}

team_t team = {
    "Micah Moore Felicia Seo",
    "Micah Moore",
    "micahmoore@vt.edu",
    "Felicia Seo",
    "seofelicia@vt.edu",
};