模拟内存分配器1

调用mm_malloc函数分配一个112字节的块，存入一个字符串，统计该字符串的长度，然后调用mm_free函数释放申请的块；第2次调用mm_malloc函数分配一个n*sizeof(int)字节块，存入n个整型元素，再释放该块。

#include <stdio.h>
#include <errno.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
/* Basic constants and macros */
#define MAX_HEAP  (1<<13)
 
#define WSIZE 4 /* word size (bytes) */
 
#define DSIZE 8 /* doubleword size (bytes) */
 
#define CHUNKSIZE (1<<12)
#define OVERHEAD 8 /* overhead of header and footer (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)))
 
/* private global variables */
static void *mem_heap;      /* points to first byte of the heap */
static void *mem_brk;           /* points to last byte of the heap */
static void *mem_max_addr;     /* max virtual address for the heap */
static void *heap_listp;
static void *rover;
 
void mem_init(void);
void *mem_sbrk(int incr);
int mm_init(void);
static void *extend_heap(size_t words);
void mm_free(void *bp);
static void *coalesce(void *bp);
void *mm_malloc(size_t size);
static void *find_fit(size_t asize);
static void place(void *bp, size_t asize);
 /*
 * mem_init- initializes the memory system model
 */
 void mem_init()
 {
  mem_heap=malloc(MAX_HEAP);   /* models available VM */
  mem_brk= mem_heap;      /* heap is initially empty */
  mem_max_addr= (char *)(mem_heap+ MAX_HEAP);  /* Max legal heap addr plus 1 */
 }
 
 /*
 * mem_sbrk- simple model of the sbrk function.Extends the heap
* by incr bytes and returns the start address of the new area. In
 * this model,the heap can not be shrunk.
 */
 void *mem_sbrk(int incr)
 {
   void *old_brk=mem_brk;
 
   if ( (incr< 0)|| ((mem_brk+ incr)>mem_max_addr)){
      errno=ENOMEM;
      fprintf(stderr,"ERROR: mem_sbrk failed. Ran out of memory...\n");
      return (void*)-1;
    }
 mem_brk+=incr;
 return old_brk;
 }
 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+WSIZE, PACK(OVERHEAD, 1)); /* prologue header */
  PUT(heap_listp+DSIZE, PACK(OVERHEAD, 1)); /* prologue footer */
  PUT(heap_listp+WSIZE+DSIZE, PACK(0, 1)); /* epilogue header */
  heap_listp += DSIZE;
  rover=heap_listp;
  /* Extend the empty heap with a free block of CHUNKSIZE bytes */
  if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
    return -1;
  return 0;
}
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);
}
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 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));
    return(bp);
  }
  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));
    return(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));
    return(PREV_BLKP(bp));
  }
  /* Make sure the rover isn't pointing into the free block*/
  /* that we just coalesced*/
 if (((char*)rover> (char*)bp)&&((char*)rover< NEXT_BLKP(bp)))
   rover=bp;
}
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 = DSIZE + OVERHEAD;
  else
    asize = DSIZE * ((size +(OVERHEAD) +(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 void *find_fit(size_t asize)    /* performs a next-fit search */
{
   char *oldrover;

   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;(char*)rover<oldrover; rover= NEXT_BLKP(rover))
   if(!GET_ALLOC(HDRP(rover))&& (asize<=GET_SIZE(HDRP(rover))))
     return rover;

 return NULL;  /* no fit found */
 }

static void place(void *bp, size_t asize)
{
  size_t csize = GET_SIZE(HDRP(bp));
  if ((csize - asize) >= (DSIZE + OVERHEAD)) {
    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));
  }
}
 
int main()
{
    int i,n=20,sum=0;
    size_t  nums;
    char *p;
    int *q;
    nums=100; 
    mem_init();
    mm_init();
    p=mm_malloc(nums);
    if (p == NULL) {
      printf("Malloc failed!\n");
      return  -1;
    }
    strncpy(p, "abvc123456789QWERTYUIOPkjhtyui897asdfghjklqazxcswed", 99);
    p[99] = '\0';
    for(i=0;p[i]!='\0';i++)
      sum++;
    printf("num of characters is %d\n",sum);
    
   
    q=(int *)mm_malloc(n*sizeof(int));
    
    if (q == NULL) {
      perror("malloc");
      exit(1);
    }
    for (i=0; i<n; i++)
	  q[i] = i;
    for(i=0;i<n;i++)
      printf("%d ",q[i]);
    printf("\n");
    mm_free(q);

    return 0;  
 
}
 
 
 

num of characters is 51

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19