www.pudn.com > !!malloc参考代码与注释.zip > my_malloc.c

#include  
#include  
 
typedef long Align; 
union header { 
	struct { 
		union header *next; 
		unsigned int size; 
	} s; 
	Align x; 
}; 
 
typedef union header Header; 
 
#define NALLOC 1024 
static Header* Moresys(unsigned int nu); 
void* Malloc(unsigned int nbytes); 
void Free(void *ap); 
 
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 = 1; 
	} 
	for (p = prev->s.next; ; p = p->s.next, prev = p) { 
		if (p->s.size >= nunits) { 
			if (p->s.size <= (nunits + 1)) 
				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 = Moresys(nunits)) == NULL) 
		return NULL; 
	} 
} 
 
static Header* Moresys(unsigned int nu) 
{ 
	char *cp; 
	Header *up; 
	 
	if(nus.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 && bps.next); p = p->s.next) 
		if(p>=p->s.next && (bp>p || bps.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.next: %X, base.next.next: %X, free: %X\n",  
	&base, base.s.next, base.s.next->s.next, free_list); 
	for (p = base.s.next; p != &base; p = p->s.next) { 
		i++; 
		printf("block %d, size=%d", i, p->s.size); 
		if(p > free_list) 
			printf(" It is not searched after this point. \n"); 
		else 
			printf(" It is a searched free block!\n"); 
	} 
} 
	 
main() 
{ 
	char *p[200]; 
	int i; 
	 
	for(i = 0; i < 20; i++ ) { 
		p[i] = (char *)Malloc(8); 
		printf("malloc %d, %X\n", i , p[i]); 
		print_list(); 
	} 
	 
	for (i =0; i < 20; i++) { 
		Free(p[i]); 
		printf("free %d\n", i); 
		print_list(); 
	} 
	return; 
}