代码生成(实现写回策略的 Cache)
时间: 2023-08-05 14:21:50 浏览: 53
下面是一个简单的 C++ 代码实现,用于说明实现写回策略的 Cache 的基本思路:
```c++
#include <iostream>
#include <map>
using namespace std;
const int CACHE_SIZE = 4; // 缓存大小
const int BLOCK_SIZE = 4; // 缓存块大小
const int MEM_SIZE = 16; // 内存大小
class Cache {
public:
Cache() {
for (int i = 0; i < CACHE_SIZE; i++) {
valid[i] = false;
dirty[i] = false;
}
}
int read(int address) {
int blockNumber = address / BLOCK_SIZE;
int blockOffset = address % BLOCK_SIZE;
int cacheIndex = findCacheBlock(blockNumber);
if (cacheIndex == -1) {
cacheIndex = allocateCacheBlock(blockNumber);
}
return cache[cacheIndex][blockOffset];
}
void write(int address, int value) {
int blockNumber = address / BLOCK_SIZE;
int blockOffset = address % BLOCK_SIZE;
int cacheIndex = findCacheBlock(blockNumber);
if (cacheIndex == -1) {
cacheIndex = allocateCacheBlock(blockNumber);
}
dirty[cacheIndex] = true;
cache[cacheIndex][blockOffset] = value;
}
void flush() {
for (int i = 0; i < CACHE_SIZE; i++) {
if (valid[i] && dirty[i]) {
int blockNumber = tag[i];
for (int j = 0; j < BLOCK_SIZE; j++) {
int address = blockNumber * BLOCK_SIZE + j;
memory[address] = cache[i][j];
}
}
valid[i] = false;
dirty[i] = false;
}
}
private:
int tag[CACHE_SIZE];
bool valid[CACHE_SIZE];
bool dirty[CACHE_SIZE];
int cache[CACHE_SIZE][BLOCK_SIZE];
int memory[MEM_SIZE];
int findCacheBlock(int blockNumber) {
for (int i = 0; i < CACHE_SIZE; i++) {
if (valid[i] && tag[i] == blockNumber) {
return i;
}
}
return -1;
}
int allocateCacheBlock(int blockNumber) {
int cacheIndex = evictCacheBlock();
if (valid[cacheIndex] && dirty[cacheIndex]) {
writeBack(cacheIndex);
}
valid[cacheIndex] = true;
tag[cacheIndex] = blockNumber;
for (int i = 0; i < BLOCK_SIZE; i++) {
int address = blockNumber * BLOCK_SIZE + i;
cache[cacheIndex][i] = memory[address];
}
return cacheIndex;
}
int evictCacheBlock() {
for (int i = 0; i < CACHE_SIZE; i++) {
if (!valid[i]) {
return i;
}
}
return 0;
}
void writeBack(int cacheIndex) {
int blockNumber = tag[cacheIndex];
for (int i = 0; i < BLOCK_SIZE; i++) {
int address = blockNumber * BLOCK_SIZE + i;
memory[address] = cache[cacheIndex][i];
}
}
};
int main() {
Cache cache;
cache.write(0, 10);
cache.write(1, 20);
cache.write(2, 30);
cache.write(3, 40);
cout << cache.read(0) << endl; // 10
cout << cache.read(1) << endl; // 20
cache.write(1, 25);
cache.flush();
cout << cache.read(1) << endl; // 25
return 0;
}
```
在这个例子中,我们实现了一个 4 个缓存块大小的 Cache,每个缓存块大小为 4 字节。当 CPU 需要读取或写入一个地址时,Cache 会根据地址的块号和块内偏移量找到相应的缓存块,如果该缓存块已经在 Cache 中,则直接读取或写入缓存;否则,Cache 会将该缓存块从主存中读入到 Cache 中,并将该缓存块标记为有效的。在写入缓存时,Cache 会将该缓存块标记为脏块,表示该缓存块已被修改过,需要在替换该缓存块时将其写回主存。在写回所有脏块时,Cache 会检查每个脏块是否在 Cache 中,并将其写回主存。