我是否使用按位移位正确提取了这些字段? (标签，索引，偏移量) [英] Am I extracting these fields correctly using bitwise shift? (tag, index, offset)

问题描述

我正在用C语言构建一个CPU缓存模拟器.我希望您能告诉我是否正确提取了这些字段:

I am building a CPU cache emulator in C. I was hoping you could tell me if I am extracting these fields correctly:

32位地址应按以下方式分解:

+---------------------------------------------------+
| tag (20 bits) | index (10 bits) | offset (2 bits) |
+---------------------------------------------------+

这是我的代码，用于获取每个值:

Here is my code to obtain the values for each:

void extract_fields(unsigned int address){

   unsigned int tag, index, offset;

   // Extract tag
   tag = address >> 12;

   // Extract index
   index = address << 20;
   index = index >> 22;

   // Extract offset
   offset = address << 30;
   offset = offset >> 30;

}

任何建议都非常感谢！

推荐答案

看起来您的解决方案可以工作，但是通常以不同的方式完成，可能会更清楚.

It looks like your solution works, but it is often done a different way that is probably a bit more clear.

以您的示例为例:

// Shift off the lowest 12 bits, and mask off the higher ones
tag = (address >> 12) & 0xFFFFF; 

// Shift off the lowest 2 bits, and mask off the higher ones
index = (address >> 2) & 0x3FF;

// Shift off the lowest 0 bits, and mask off the higher ones
offset = (address >> 0) & 0x3;

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