realloc implementation

realloc

void *realloc(void *ptr, size_t size)
{
	char *p;
	char *a = ptr;

	// Realloc on a NULL pointer same as malloc.
	if (ptr == NULL)
	{
		p = malloc(size);
		return p;
	}

	// Realloc to size 0 same as free.
	else if (size == 0)
	{
		free(ptr);
		return NULL;
	}

	// Cannot realloc to size smaller.
	else if(size > *(a - 8)){
		return NULL;
	}

	// Malloc and copy to given pointer, then free the temporary portion.
	else
	{
		p = malloc(size);
		bcopy(ptr, p, size);
		free(p);
		return p;
	}
}