mm_impl.c

/*
 * mm.c
 *
 * NOTE TO STUDENTS: Replace this header comment with your own header
 * comment that gives a high level description of your solution.
 */
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include "mm.h"
#include "memlib.h"

/* If you want debugging output, use the following macro.  When you hand
 * in, remove the #define DEBUG line. */
#define DEBUG
#ifdef DEBUG
# define dbg_printf(...) printf(__VA_ARGS__)
#else
# define dbg_printf(...)
#endif


/* do not change the following! */
#ifdef DRIVER
/* create aliases for driver tests */
#define malloc mm_malloc
#define free mm_free
#define realloc mm_realloc
#define calloc mm_calloc
#endif /* def DRIVER */

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

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


/*
 * If NEXT_FIT defined use next fit search, else use first fit search 
 */
//#define NEXT_FIT
#define BEST_FIT

/* $begin mallocmacros */
/* Basic constants and macros */
#define WSIZE       4       /* Word and header/footer size (bytes) */ //line:vm:mm:beginconst
#define DSIZE       8       /* Doubleword size (bytes) */
#define CHUNKSIZE  (1<<12)  /* Extend heap by this amount (bytes) */  //line:vm:mm:endconst 

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

/* Pack a size and allocated bit into a word */
#define PACK(size, alloc)  ((size) | (alloc)) //line:vm:mm:pack

/* Read and write a word at address p */
#define GET(p)       (*(unsigned int *)(p))            //line:vm:mm:get
#define PUT(p, val)  (*(unsigned int *)(p) = (val))    //line:vm:mm:put

/* Read the size and allocated fields from address p */
#define GET_SIZE(p)  (GET(p) & ~0x7)                   //line:vm:mm:getsize
#define GET_ALLOC(p) (GET(p) & 0x1)                    //line:vm:mm:getalloc

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

/* Given block ptr bp, compute address of next and previous blocks */
#define NEXT_BLKP(bp)  ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE))) //line:vm:mm:nextblkp
#define PREV_BLKP(bp)  ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE))) //line:vm:mm:prevblkp
/* $end mallocmacros */

/* Global variables */
static char *heap_listp = 0;  /* Pointer to first block */  
#ifdef NEXT_FIT
static char *rover;           /* Next fit rover */
#endif


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

#define SIZE_PTR(p)  ((size_t*)(((char*)(p)) - SIZE_T_SIZE))

/* Function prototypes for internal helper routines */
static void *extend_heap(size_t words);
static void place(void *bp, size_t asize);
static void *find_fit(size_t asize);
static void *coalesce(void *bp);
static void printblock(void *bp); 
static void checkheap(int verbose);
static void checkblock(void *bp);


/*
 * Initialize: return -1 on error, 0 on success.
 */
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);                     


	#ifdef NEXT_FIT
    	rover = heap_listp;
	#endif
    /* Extend the empty heap with a free block of CHUNKSIZE bytes */
	if (extend_heap(CHUNKSIZE/WSIZE) == NULL) 
		return -1;
    return 0;
}
/* $end mminit */



/*
 * malloc
 */
void *malloc (size_t size) {
    size_t asize;      /* Adjusted block size */
    size_t extendsize; /* Amount to extend heap if no fit */
    char *bp;      

/* $end mmmalloc */
    if (heap_listp == 0){
		mm_init();
    }
/* $begin mmmalloc */
    /* Ignore spurious requests */
    if (size == 0)
	return NULL;

    /* Adjust block size to include overhead and alignment reqs. */
    if (size <= DSIZE)                                          //line:vm:mm:sizeadjust1
		asize = 2*DSIZE;                                        //line:vm:mm:sizeadjust2
    else
		asize = DSIZE * ((size + (DSIZE) + (DSIZE-1)) / DSIZE); //line:vm:mm:sizeadjust3

    /* Search the free list for a fit */
    if ((bp = find_fit(asize)) != NULL) {  //line:vm:mm:findfitcall
		place(bp, asize);                  //line:vm:mm:findfitplace
	return bp;
    }

    /* No fit found. Get more memory and place the block */
    extendsize = MAX(asize,CHUNKSIZE);                 //line:vm:mm:growheap1
    if ((bp = extend_heap(extendsize/WSIZE)) == NULL)  
		return NULL;                                  //line:vm:mm:growheap2
    place(bp, asize);                                 //line:vm:mm:growheap3
    return bp;
}

/* 
 * mm_free - Free a block 
 */
/* $begin mmfree */
void mm_free(void *bp)
{

    printf("In Free \n");
    if(bp == 0) 
	   return;

    size_t size = GET_SIZE(HDRP(bp));
    if (heap_listp == 0){
	   mm_init();
    }
    PUT(HDRP(bp), PACK(size, 0));
    PUT(FTRP(bp), PACK(size, 0));
    coalesce(bp);
}

/*
 * coalesce - Boundary tag coalescing. Return ptr to coalesced block
 */
/* $begin mmfree */
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);
    }
/* $end mmfree */
#ifdef NEXT_FIT
    /* Make sure the rover isn't pointing into the free block */
    /* that we just coalesced */
    if ((rover > (char *)bp) && (rover < NEXT_BLKP(bp))) 
	rover = bp;
#endif
/* $begin mmfree */
    return bp;
}
/* $end Coalesce*/



/*
 * mm_realloc - Naive implementation of realloc
 */
void *mm_realloc(void *ptr, size_t size)
{
    size_t oldsize;
    void *newptr;

    /* If size == 0 then this is just free, and we return NULL. */
    if(size == 0) {
    	mm_free(ptr);
	return 0;
    }

    /* If oldptr is NULL, then this is just malloc. */
    if(ptr == NULL) {
	return mm_malloc(size);
    }

    newptr = mm_malloc(size);

    /* If realloc() fails the original block is left untouched  */
    if(!newptr) {
	return 0;
    }

    /* Copy the old data. */
    oldsize = GET_SIZE(HDRP(ptr));
    if(size < oldsize) oldsize = size;
    memcpy(newptr, ptr, oldsize);

    /* Free the old block. */
    mm_free(ptr);

    return newptr;
}
/*
 * calloc - you may want to look at mm-naive.c
 * This function is not tested by mdriver, but it is
 * needed to run the traces.
 */
void *calloc (size_t nmemb, size_t size) {
      size_t bytes = nmemb * size;
  void *newptr;

  newptr = malloc(bytes);
  memset(newptr, 0, bytes);

  return newptr;
}


/*
 * Return whether the pointer is in the heap.
 * May be useful for debugging.
 */
/*static int in_heap(const void *p) {
    return p <= mem_heap_hi() && p >= mem_heap_lo();
}


 * Return whether the pointer is aligned.
 * May be useful for debugging.
 
static int aligned(const void *p) {
    return (size_t)ALIGN(p) == (size_t)p;
}*/

/*
 * mm_checkheap
 */
/**
 * mm_checkheap - Function, to call checkheap as per verbose value
 * @param verbose value determines what things to print in checkheap
 */
void mm_checkheap(int verbose) {
	/*Get gcc to be quiet. */
	 verbose = verbose;
     checkheap(9);
}

/* 
 * extend_heap - Extend heap with free block and return its block pointer
 */
/* $begin mmextendheap */
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; //line:vm:mm:beginextend
    if ((long)(bp = mem_sbrk(size)) == -1)  
	return NULL;                                        //line:vm:mm:endextend

    /* Initialize free block header/footer and the epilogue header */
    PUT(HDRP(bp), PACK(size, 0));         /* Free block header */   //line:vm:mm:freeblockhdr
    PUT(FTRP(bp), PACK(size, 0));         /* Free block footer */   //line:vm:mm:freeblockftr
    PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1)); /* New epilogue header */ //line:vm:mm:newepihdr

    /* Coalesce if the previous block was free */
    return coalesce(bp);                                          //line:vm:mm:returnblock
}
/* $end mmextendheap */

/* 
 * place - Place block of asize bytes at start of free block bp 
 *         and split if remainder would be at least minimum block size
 */
/* $begin mmplace */
/* $begin mmplace-proto */
static void place(void *bp, size_t asize)
     /* $end mmplace-proto */
{
    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));
    }
}
/* $end mmplace */

/* 
 * find_fit - Find a fit for a block with asize bytes 
 */
/* $begin mmfirstfit */
/* $begin mmfirstfit-proto */
static void *find_fit(size_t asize)
{
/* $end mmfirstfit */

#ifdef NEXT_FIT 
    /* Next fit search */
    char *oldrover = rover;

    /* Search from the rover to the end of list */
    for ( ; GET_SIZE(HDRP(rover)) > 0; rover = NEXT_BLKP(rover))
	if (!GET_ALLOC(HDRP(rover)) && (asize <= GET_SIZE(HDRP(rover))))
	    return rover;

    /* search from start of list to old rover */
    for (rover = heap_listp; rover < oldrover; rover = NEXT_BLKP(rover))
	if (!GET_ALLOC(HDRP(rover)) && (asize <= GET_SIZE(HDRP(rover))))
	    return rover;

    return NULL;  /* no fit found */
#elif defined BEST_FIT

	/* Best fit search */
    void *bp;
    void *temploc;
    temploc = NULL;
    unsigned int temploc_size=INT_MAX;
    unsigned int curr_size=INT_MAX;
    for (bp = heap_listp; (curr_size = GET_SIZE(HDRP(bp))) > 0; bp = NEXT_BLKP(bp)) {
		if( !GET_ALLOC(HDRP(bp)) && ( asize <= curr_size ) && temploc_size >  curr_size ) {
			temploc = bp;
			temploc_size = curr_size;
		}
    }

    return temploc;
#else
/* $begin mmfirstfit */
    /* 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 */
/* $end mmfirstfit */
#endif

}

static void printblock(void *bp) 
{
    size_t hsize, halloc, fsize, falloc;

    checkheap(0);
    hsize = GET_SIZE(HDRP(bp));
    halloc = GET_ALLOC(HDRP(bp));  
    fsize = GET_SIZE(FTRP(bp));
    falloc = GET_ALLOC(FTRP(bp));  

    if (hsize == 0) {
	printf("%p: EOL\n", bp);
	return;
    }

    /*  printf("%p: header: [%p:%c] footer: [%p:%c]\n", bp, 
	hsize, (halloc ? 'a' : 'f'), 
	fsize, (falloc ? 'a' : 'f')); */
}

static void checkblock(void *bp) 
{
    if ((size_t)bp % 8)
	printf("Error: %p is not doubleword aligned\n", bp);
    if (GET(HDRP(bp)) != GET(FTRP(bp)))
	printf("Error: header does not match footer\n");
}

/* 
 * checkheap - Minimal check of the heap for consistency 
 */
void checkheap(int verbose) 
{
    char *bp = heap_listp;

    if (verbose)
	printf("Heap (%p):\n", heap_listp);

    if ((GET_SIZE(HDRP(heap_listp)) != DSIZE) || !GET_ALLOC(HDRP(heap_listp)))
	printf("Bad prologue header\n");
    checkblock(heap_listp);

    for (bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp)) {
	if (verbose) 
	    printblock(bp);
	checkblock(bp);
    }

    if (verbose)
	printblock(bp);
    if ((GET_SIZE(HDRP(bp)) != 0) || !(GET_ALLOC(HDRP(bp))))
	printf("Bad epilogue header\n");
}