CSAPP | Representing and Manipulating Information

最新推荐文章于 2024-06-22 21:17:38 发布

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#学习笔记

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本文探讨了虚拟内存的概念，即通过结合DRAM、闪存、磁盘存储等资源，为程序提供一个统一的大容量字节数组视图。此外，还深入解析了位掩码操作与位移运算的原理及其在数据处理中的应用。

Virtual Memory: a very large array of bytes --> combination of DRAM, flash memory, disk storage, special hardware, and operating system software to provide the program with what appears to be a monolithic byte array

Masking Operations: a mask is a bit pattern that indicates a selected set of bits within a word (e.g. x & 0xFF yields a value consisting of the least significant byte of x, with all other bytes set to 0)

Right Shift:

Logical: fills left end with k zeros
Arithmetic: fills left end with k repetition of the most significant bit (useful for operating on signed integer data)

Principle:

Uniqueness of unsigned encoding: [bijection]
$B 2 U w$ (bit vector of length w -> a unique number between 0 and $2^w - 1$ ) and
$U 2 B w$ (a number between 0 and $2^w - 1$ -> a unique bit vector of length w)
Uniqueness of two’s complement encoding: [bijection]