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沒有什么難以理解的地方

static void *heap_listp;extern int mm_init(void); extern void *mm_malloc(size_t size); extern void mm_free(void *ptr);static void *extend_heap(size_t words); static void *coalesce(void *bp); static void *find_fit(size_t asize); static void *place(void *bp,size_t asize); /*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 amout (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 workd 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,comute 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) {/*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 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)); /*New block header and Free Epilogue*/PUT(FTRP(bp),PACK(size,0)); /*New 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));}else if(!prev_alloc && !next_alloc) { /*Case 3*/size+=GET_SIZE(HDRP(PREV_BLKP(bp)));PUT(HDRP(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));}return 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=2*DSIZE;else asize=DSIZE*((size+(DSIZE)+(DSIZE-1))/DSIZE); /*judge size*//*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) {char *bp = (heap_listp+DSIZE); /*get first block*/size_t this_alloc=GET_ALLOC(HDRP(NEXT_BLKP(bp))); /*judge if 0*/size_t this_size=GET_SIZE(HDRP(bp)); /*get size*/while(!(this_alloc == 0x1 && this_size == 0)) { /*scan the list*/if(this_alloc == 0x0 && this_size >= asize) return bp; /*get the good block*/bp=NEXT_BLKP(bp); /*get the next one*/this_alloc=GET_ALLOC(HDRP(NEXT_BLKP(bp))); this_size=GET_SIZE(HDRP(bp));}return NULL; /*bad scan*/ }static void *place(void *bp,size_t asize){size_t old_size=GET_SIZE(HDRP(bp)); /*save old size*/if(asize == old_size) { /*same size*/PUT(HDRP(bp),PACK(asize,1));PUT(FTRP(bp),PACK(asize,1));}else { /*samller size*/size_t rem_size=old_size-asize; /*get the remain size*/PUT(HDRP(bp),PACK(asize,1)); /*set the alloc*/PUT(FTRP(bp),PACK(asize,1));void *next_bp=NEXT_BLKP(bp);PUT(HDRP(next_bp),PACK(rem_size,0)); /*set alloc and size*/PUT(FTRP(next_bp),PACK(rem_size,0));} }

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下面是memlib?? 注意MAX_HEAP 不要取太大不然開不了

#define MAX_HEAP (1<<20)/*Private global variables*/static char *mem_heap; /*Points to first byte of heap*/ static char *mem_brk; /*Points to last byte of heap plus 1*/ static char *mem_max_addr; /*Max legal heap addr plus 1*//**mem_init - Initialize the memory system model*/void mem_init(void) {mem_heap = (char*)malloc(MAX_HEAP);mem_brk = (char*)mem_heap;mem_max_addr = (char*)(mem_heap + MAX_HEAP); }/**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 cannot be shrunk.*/void *mem_sbrk(int incr) {char *old_brk = mem_brk;if((incr < 0) || ((mem_brk + incr) > mem_max_addr)) {errno = ENOMEM;fprintf(stderr,"ERROR: memsbrk failed. Ran out of memory ...\n");return (void*)-1;}mem_brk+=incr;return (void*)old_brk; }

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加上相應的庫函數就可以運行了.不過問題是mm_free有沒有很好的工作我還沒想到很好的方法檢驗.

轉載于:https://www.cnblogs.com/tclan126/p/8413499.html

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