LRU页面置换算法

Posted 2020-07-31 A_book

LRU

本文以序列长度20的{ 7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0,1,7,0,1};以及页面4；为例；

 1 #include <stdio.h>
 2 
 3 #define InitPysiBlocks 4
 4 #define MaxPages 20
 5 int PysicalBlocks[InitPysiBlocks] = { -1,-1,-1,-1 };
 6 int PageSequence[MaxPages] = { 7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0,1,7,0,1};
 7 
 8 void LRU(int py[],int pg[])
 9 {
10     int i,j,k,m,flag[MaxPages],temp[MaxPages][InitPysiBlocks];
11     int max = 0;
12     char f[MaxPages];
13     for(i = 0; i < InitPysiBlocks; i++)
14     {
15         py[i] = pg[i];
16         flag[i] = i;
17         f[i] = \'*\';
18         for(j = 0; j < InitPysiBlocks; j++)
19             temp[i][j] = py[j];
20     }
21     for(i = InitPysiBlocks; i < MaxPages; i++)
22     {
23         for(j = 0,k = 0; j < InitPysiBlocks; j++)
24         {
25             if(py[j] != pg[i])
26                 k++;
27             else
28                 flag[j] = i;
29         }
30         if(k == InitPysiBlocks)
31         {
32             f[i] = \'*\';
33             max = flag[0] < flag[1]?0:1;
34             for(m = 2; m < InitPysiBlocks; m++)
35                 if(flag[m] < flag[max])
36                     max = m;
37             py[max] = pg[i];
38             flag[max] = i;
39             for(j = 0; j < InitPysiBlocks; j++)
40                 temp[i][j] = py[j];
41         }
42         else
43         {
44             f[i] = \' \';
45             for(j = 0; j < InitPysiBlocks; j++)
46                 temp[i][j] = py[j];
47         }
48     }
49     printf("输出结果为下表(-1代表为空,*代表有缺页)：\\n");
50     for(i = 0; i < InitPysiBlocks; i++)
51     {
52         for(j = 0; j < MaxPages; j++)
53             printf("%3d",temp[j][i]);
54         printf("\\n");
55     }
56     for(i = 0; i < MaxPages; i++)
57         printf("%3c",f[i]);
58     printf("\\n");
59 }
60 
61 void main()
62 {
63     LRU(PysicalBlocks,PageSequence);
64 }

测试：