# linux2021: adamtsai

## 測驗 α-1

Linux kernel bit rotation operation source:
`include/linux/bitops.h`: roll*, rolr*
:::warning
TODO: Illustrate the use cases inside the Linux kernel.
:::

Bit rotation or whatever any of bitwise operation are very essential
operations. You can find there are lots of usage in hashcode like SHA,
checksum, etc.

## 測驗 α-2

may be, cause there are some discussion in gcc mailing list about the optimization for common constructs of bit operation.
FYI, https://gcc.gnu.org/legacy-ml/gcc-patches/2007-11/msg01112.html
:::warning
TODO: analyze the IR generated by GCC and see if the optimizer really works as expected.
:::

## 測驗 β-1

For power of 2 cases, alignment can be done with bit clear simply.
It is a trivial problem.
:::warning
Can you write an efficient implementation which deals with **any** sizes of alignments?
:::

## 測驗 β-2

There are various power of 2 round up/down macros in Linux kernel.

They are used in lots of places. For what I most familier with, block layer or filesytem use them to calculate the maximum size of data they can handle at a time.