malloc.c

内 存 的 申 请 与 释 放 简单的程序

#include <unistd.h>
#include "Malloc.h"
static Header base;
static Header *free_list=NULL;
void *Malloc(unsigned int nbytes)
{
	Header *p,*prev;
	unsigned int nunits;
	nunits=(nbytes+sizeof(Header)-1)/sizeof(Header)+1;
		if((prev=free_list)==NULL){
			base.s.next=free_list=prev=&base;
			base.s.size=0;
		}
		for (p=prev->s.next;;prev=p,p=p->s.next){
			if(p->s.size>=nunits){
				if(p->s.size==nunits)
					prev->s.next=p->s.next;
				else{
					p->s.size-=nunits;
					p+=p->s.size;
					p->s.size=nunits;
				}
				free_list=prev;
				return(void*)(p+1);
			}
			if(p==free_list)
				if((p=morecore(nunits))==NULL)
					return NULL;
			}
}
static Header *morecore(unsigned int nu)
{
	char *cp;
	Header *up;
	if (nu<NALLOC)
	nu=NALLOC;
	cp=sbrk(nu * sizeof(Header));
	printf("sbrk:%x--%x\n",cp,cp+nu * sizeof(Header));
	if(cp==(char*)-1)
		return NULL;
	up=(Header *)cp;
	up->s.size=nu;
	Free(up+1);
	return free_list;
}
void Free(void *ap)
{
	Header *bp,*p;
	bp=(Header *)ap-1;
	for (p=free_list; !(bp>p && bp<p->s.next);p=p->s.next)
		if (p>=p->s.next && (bp>p || bp<p->s.next))
			break;
	if(bp+bp->s.size==p->s.next){
		bp->s.size+=p->s.next->s.size;
		bp->s.next=p->s.next->s.next;
	}
	else
		bp->s.next=p->s.next;
		if(p+p->s.size==bp){
			p->s.size+=bp->s.size;
			p->s.next=bp->s.next;
		}
		else
			p->s.next=bp;
			free_list=p;
}
void print_list(void)
{
	Header * p;
	int i=0;
	printf("base:%x,base.nest:%x,base.next.next:%x,free:%x\n",&base, base.s.next,base.s.next->s.next,free_list); 
	for(p=&base;p->s.next !=free_list;p=p->s.next){
		i++;
		printf("block %d,size=%d",i,p->s.size);
		if(p>free_list)
			printf("It is not searched afrer this point.\n");
		else
			printf("It is a searched free block!\n");
	}
}