addl $0x1,0xXXXXXXXX 코드의 사용중에 결과가 이상하게 나옵니다...

#include <stdio.h>
#include <pthread.h>
#define NUM_THREAD	100
 
void * thread_inc(void * arg);
void * thread_des(void * arg);
 
int num=0;
 
int main(int argc, char *argv[]) 
{
	pthread_t thread_id[NUM_THREAD];
	int i;
 
	for(i=0; i<NUM_THREAD; i++)
	{
		if(i%2)
			pthread_create(&(thread_id[i]), NULL, thread_inc, NULL);
		else
			pthread_create(&(thread_id[i]), NULL, thread_des, NULL);	
	}	
 
	for(i=0; i<NUM_THREAD; i++)
		pthread_join(thread_id[i], NULL);
 
	printf("result: %d \n", num);
	return 0;
}
 
void * thread_inc(void * arg) 
{
	int i;
	for(i=0; i<100000; i++)
		num+=1; <--- (1)
	return NULL;
}
void * thread_des(void * arg)
{
	int i;
	for(i=0; i<100000; i++)
		num-=1; <--- (2)
	return NULL;
}

804862f:  a1 2c a0 04 08    mov    0x804a02c,%eax
8048634: 83 c0 01              add    $0x1,%eax
8048637: a3 2c a0 04 08    mov    %eax,0x804a02c
( 0x804a02c 는 num전역변수 주소 )

804862f: 83 05 2c a0 04 08 01  addl   $0x1,0x804a02c
8048636: 90                               nop
8048637: 90                               nop
8048638: 90                               nop
8048639: 90                               nop
804863a: 90                               nop
804863b: 90                               nop
( 0x804a02c 는 num전역변수 주소 )

804865f: a1 2c a0 04 08        mov    0x804a02c,%eax
8048664: 83 e8 01                 sub    $0x1,%eax
8048667: a3 2c a0 04 08        mov    %eax,0x804a02c
( 0x804a02c 는 num전역변수 주소 )

804865f: 83 2d 2c a0 04 08 01  subl   $0x1,0x804a02c
8048666: 90                               nop
8048667: 90                               nop
8048668: 90                               nop
8048669: 90                               nop
804866a: 90                               nop
804866b: 90                               nop
( 0x804a02c 는 num전역변수 주소 )