changepage_opt.c

一些操作系统课程实验的程序

void ChangePage_OPT(int instr_addr, Page * page, int page_num, int *instruction_array, int cur)
{
	int i, ptr,j,count;
	int p[32] = {0};
	j = 0;
	count = 0;
	ptr = 0;
	/*首先找是否空闲的内存块，即page_id等于-1*/
	for (i=0; i<page_num; i++)
	{
		if (page[i].page_id == -1)
		{
			page[i].page_id = instr_addr / 10;
			page[i].used_count = 1;
			page[i].last = cur;
			return;
		}
	}
	for (i=0; i<page_num; i++)
	{ /*找出内存中每一页在后续的指令序列中再次出现的序号，若没有再次出现则序号记为INSTRUCTION_NUM，
		把其中有最大值的页替换*/
		for (j=cur; j<INSTRUCTION_NUM; j++)
		{
			if (page[i].page_id == (instruction_array[j] / 10))
			{
				p[i] = j;
				count++;
				break;
			}
		}
		if (p[i] == 0)
		{
			p[i] = INSTRUCTION_NUM;
		}
		if (count == page_num)
			break;
	}
	for (i=1; i<page_num; i++)
	{
		if (p[i] > p[ptr])
		{
			ptr = i;
		}
	}
	page[ptr].page_id = instr_addr / 10;
	page[ptr].used_count = 1;
	page[ptr].last = cur;
}