malloclab

首先从 csapp 599 页开始照着抄,用的是隐式空闲链表。

发现没有 realloc,那只能自己捏造一个了……

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/*
* mm_realloc - Implemented simply in terms of mm_malloc and mm_free
*/
void *mm_realloc(void *bp, size_t size) {
int asize;
if(size==0)
return NULL;
if(size<=DSIZE)
asize = 2 * DSIZE;
else
asize = DSIZE * ((size + DSIZE + DSIZE - 1) / DSIZE);
size_t oldsize=GET_SIZE(HDRP(bp));
if(oldsize>asize) {
PUT(HDRP(bp), PACK(asize, 1));
PUT(FTRP(bp), PACK(asize, 1));
PUT(HDRP(NEXT_BLKP(bp)), PACK(oldsize-asize, 0));
PUT(FTRP(NEXT_BLKP(bp)), PACK(oldsize-asize, 0));
coalesce(NEXT_BLKP(bp));
return bp;
}
else if(oldsize<asize) {
if(!GET_ALLOC(HDRP(NEXT_BLKP(bp))) && GET_SIZE(HDRP(NEXT_BLKP(bp)))+oldsize>=asize) {
int newsize=GET_SIZE(HDRP(NEXT_BLKP(bp)))+oldsize;
PUT(HDRP(bp), PACK(newsize, 0));
PUT(FTRP(bp), PACK(newsize, 0));
place(bp, asize);
coalesce(NEXT_BLKP(bp));
return bp;
}
else {
void *newptr;
size_t copySize;
newptr = mm_malloc(asize);
if (newptr == NULL)
return NULL;
copySize = GET_SIZE(HDRP(bp));
if (asize < copySize)
copySize = asize;
memcpy(newptr, bp, copySize);
mm_free(bp);
return newptr;
}
}
else
return bp;
}

这样你的 perf 能获得 66 分的好成绩,感天动地。

书抄完了,开始抄网上的代码吧。

这个看一看,那个看一看,懒得写平衡树,那就随便糊一个显式空闲列表+分离适配吧(603页,605页)。

在我的代码中,块的格式是:

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31       0
/--------\ 低
|header |
|--------|
|payload |
|... |
|--------|
|fill(*) |
|... |
|--------|
|footer |
\--------/ 高
分配块
31 0
/--------\ 低
|header |
|--------|
|next |
|prev |
|--------|
|fill(*) |
|... |
|--------|
|footer |
\--------/ 高
空闲

fill(*)是填充的,有可能没有。

然后抄一遍代码,自己糊一个有讨论的 realloc 就可以拿到 89 分的好成绩了。我怀疑这是因为俺的 Intel© Core™ i5-8250U CPU @ 1.60GHz × 4不太行,所以也不改了(

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/*
* 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 */
"poorpool",
/* First member's full name */
"Harry Bovik",
/* First member's email address */
"bovik@cs.cmu.edu",
/* Second member's full name (leave blank if none) */
"",
/* Second member's email address (leave blank if none) */
""
};

/* 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)))

#define WSIZE 4
#define DSIZE 8
#define CHUNKSIZE (1<<12)

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

#define PACK(size, alloc) ((size) | (alloc))

#define GET(p) (*(unsigned int *)(p))
#define PUT(p, val) (*(unsigned int *)(p) = (val))

/*对于一个void *bp来说,GET_PTR(BP)同时相当于取得他的后继,GET_PTR((unsigned int *)BP+1)相当于取得他的前驱。这里的后继前驱
都是针对显式空闲列表来说的,也就是前后的那个空闲块。务必理解这个概念*/
#define GET_PTR(p) ((unsigned int *)(long)(GET(p)))
#define PUT_PTR(p, ptr) (*(unsigned int *)(p) = ((long)(ptr)))

#define GET_SIZE(p) (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)

#define HDRP(bp) ((char *)(bp) - WSIZE)
#define FTRP(bp) ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)

#define NEXT_BLKP(bp) ((char *)(bp) + GET_SIZE((char *)(bp) - WSIZE))
#define PREV_BLKP(bp) ((char *)(bp) - GET_SIZE((char *)(bp) - DSIZE))

static void *heap_listp;

#define SIZE1 (1<<4)
#define SIZE2 (1<<5)
#define SIZE3 (1<<6)
#define SIZE4 (1<<7)
#define SIZE5 (1<<8)
#define SIZE6 (1<<9)
#define SIZE7 (1<<10)
#define SIZE8 (1<<11)
#define SIZE9 (1<<12)
#define SIZE10 (1<<13)
#define SIZE11 (1<<14)
#define SIZE12 (1<<15)
#define SIZE13 (1<<16)
#define SIZE14 (1<<17)
#define SIZE15 (1<<18)
#define SIZE16 (1<<19)
#define SIZE17 (1<<20)

#define LISTS_NUM 18

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);
static void insert_list(void *bp);
static size_t get_list_offset(size_t size);
static void delete_list(void *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)
;
else if(prev_alloc && !next_alloc) {
delete_list(NEXT_BLKP(bp));
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) {
delete_list(PREV_BLKP(bp));
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 {
delete_list(PREV_BLKP(bp));
delete_list(NEXT_BLKP(bp));
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);
}
insert_list(bp);
return bp;
}

static void insert_list(void *bp) {
size_t size = GET_SIZE(HDRP(bp));
size_t index = get_list_offset(size);
if(GET_PTR(heap_listp+WSIZE*index)==NULL) {
PUT_PTR(heap_listp + WSIZE * index, bp);
PUT_PTR(bp, NULL);//next<->NULL
PUT_PTR((unsigned int *)bp + 1, NULL);//prev<->NULL
}
else {
PUT_PTR(bp, GET_PTR(heap_listp + WSIZE * index));//next<-原来的头节点
PUT_PTR(GET_PTR(heap_listp + WSIZE * index) + 1, bp); //头节点prev<-bp
PUT_PTR((unsigned int *)bp + 1, NULL);//bp的prev <- NULL
PUT_PTR(heap_listp + WSIZE * index, bp);//头节点 bp
}
}

static void delete_list(void *bp) {
//这就是双向链表哇
size_t size = GET_SIZE(HDRP(bp));
size_t index = get_list_offset(size);
if(GET_PTR(bp)==NULL && GET_PTR((unsigned int *)bp+1)==NULL)
PUT_PTR(heap_listp + WSIZE * index, NULL);
else if (GET_PTR(bp)==NULL && GET_PTR((unsigned int *)bp+1) != NULL) {
PUT_PTR((GET_PTR((unsigned int*)GET_PTR((unsigned int *)bp+1))), NULL );//bp->prev->next=NULL
PUT_PTR(GET_PTR((unsigned int *)bp + 1), NULL); //bp前驱指针prev=NULL
}
else if (GET_PTR(bp) != NULL && GET_PTR((unsigned int *)bp + 1) == NULL){
PUT_PTR(heap_listp + WSIZE * index, GET_PTR(bp));
PUT_PTR(GET_PTR(bp) + 1, NULL); //prev=NULL
}
else if (GET_PTR(bp) != NULL && GET_PTR((unsigned int *)bp + 1) != NULL) {
PUT_PTR(GET_PTR((unsigned int *)bp + 1), GET_PTR(bp));
PUT_PTR(GET_PTR(bp) + 1, GET_PTR((unsigned int*)bp + 1));//bp->next->prev = bp->prev
}
}

size_t get_list_offset(size_t size) {
if(size<=SIZE1)
return 0;
else if(size<=SIZE2)
return 1;
else if(size<=SIZE3)
return 2;
else if(size<=SIZE4)
return 3;
else if(size<=SIZE5)
return 4;
else if(size<=SIZE6)
return 5;
else if(size<=SIZE7)
return 6;
else if(size<=SIZE8)
return 7;
else if(size<=SIZE9)
return 8;
else if(size<=SIZE10)
return 9;
else if(size<=SIZE11)
return 10;
else if(size<=SIZE12)
return 11;
else if(size<=SIZE13)
return 12;
else if(size<=SIZE14)
return 13;
else if(size<=SIZE15)
return 14;
else if(size<=SIZE16)
return 15;
else if(size<=SIZE17)
return 16;
else
return 17;
}

static void *extend_heap(size_t words) {
char *bp;
size_t size;
size = (words % 2) ? (words + 1) * WSIZE : words * WSIZE;
if((long)(bp = mem_sbrk(size))==-1)
return NULL;
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size, 0));
PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1));
return coalesce(bp);
}
/*
* mm_init - initialize the malloc package.
*/

int mm_init(void)
{
if((heap_listp = mem_sbrk((4+LISTS_NUM)*WSIZE)) == (void *)-1)
return -1;
PUT(heap_listp + LISTS_NUM * WSIZE, 0);
PUT(heap_listp + (1 + LISTS_NUM) * WSIZE, PACK(DSIZE, 1));
PUT(heap_listp + (2 + LISTS_NUM) * WSIZE, PACK(DSIZE, 1));
PUT(heap_listp + (3 + LISTS_NUM) * WSIZE, PACK(0, 1));
int i;
for(i=0; i<LISTS_NUM; i++)
PUT_PTR(heap_listp + WSIZE * i, NULL);
if(extend_heap(CHUNKSIZE/WSIZE)==NULL)
return -1;
return 0;
}

static void *find_fit(size_t asize) {
size_t index=get_list_offset(asize);
unsigned int *ptr;
while(index<18) {
ptr = GET_PTR(heap_listp + WSIZE * index);
while(ptr!=NULL) {
if(GET_SIZE(HDRP(ptr))>=asize)
return (void *)ptr;
ptr = GET_PTR(ptr);
}
index++;
}
return NULL;
}
static void place(void *bp, size_t asize) {
size_t csize = GET_SIZE(HDRP(bp));
delete_list(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));
insert_list(bp);
}
else {
PUT(HDRP(bp), PACK(csize, 1));
PUT(FTRP(bp), PACK(csize, 1));
}
}
static void pppplace(void *bp, size_t asize) {
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));
insert_list(bp);
}
else {
PUT(HDRP(bp), PACK(csize, 1));
PUT(FTRP(bp), PACK(csize, 1));
}
}
/*
* mm_malloc - Allocate a block by incrementing the brk pointer.
* Always allocate a block whose size is a multiple of the alignment.
*/

void *mm_malloc(size_t size)
{
size_t asize;
size_t extendsize;
char *bp;
if(size==0)
return NULL;
if(size<=DSIZE)
asize = 2 * DSIZE;
else
asize = DSIZE * ((size + DSIZE + DSIZE - 1) / DSIZE);
if((bp=find_fit(asize))!=NULL) {
place(bp, asize);
return bp;
}
extendsize = MAX(asize, CHUNKSIZE);
if((bp=extend_heap(extendsize/WSIZE))==NULL)
return NULL;
place(bp, asize);
// printf("%%p:%p\n", bp);
return bp;
}

/*
* mm_free - Freeing a block does nothing.
*/
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);
}

/*
* mm_realloc - Implemented simply in terms of mm_malloc and mm_free
*/
void *mm_realloc(void *bp, size_t size)
{
size_t asize;
if(size==0)
return NULL;
if(size<=DSIZE)
asize = 2 * DSIZE;
else
asize = DSIZE * ((size + DSIZE + DSIZE - 1) / DSIZE);
if(bp == NULL)
return mm_malloc(asize);
size_t oldsize=GET_SIZE(HDRP(bp));
if(oldsize>asize)
return bp;
else if(oldsize<asize) {
if(!GET_ALLOC(HDRP(NEXT_BLKP(bp))) && GET_SIZE(HDRP(NEXT_BLKP(bp)))+oldsize>=asize) {
int newsize=GET_SIZE(HDRP(NEXT_BLKP(bp)))+oldsize;
delete_list(NEXT_BLKP(bp));
PUT(HDRP(bp), PACK(newsize, 1));
PUT(FTRP(bp), PACK(newsize, 1));
return bp;
}
else {
void *newptr;
newptr = mm_malloc(asize);
if (newptr == NULL)
return NULL;
memcpy(newptr, bp, asize);
mm_free(bp);
return newptr;
}
}
else
return bp;
}
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