Linux内核中HWEIGHT宏的目的是什么？

发布于 2025-02-02 08:01:42 字数 794 浏览 2 评论 0原文

我遇到了hweight8/hweight16/hweight32/...宏（宏）读取内核中的某些驱动程序代码时。我想了解，这些宏的目的以及它们在做什么，但不幸的是，我没有找到有关该主题的任何文档。

宏的定义看起来像这样，可以在
中找到包括/asm-generic/bitops/bitops/bitops/ const_hweight.h

#define hweight8(w)  (__builtin_constant_p(w) ? __const_hweight8(w)  : __arch_hweight8(w))
#define hweight16(w) (__builtin_constant_p(w) ? __const_hweight16(w) : __arch_hweight16(w))
#define hweight32(w) (__builtin_constant_p(w) ? __const_hweight32(w) : __arch_hweight32(w))
#define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w))

原文

I came across the hweight8/hweight16/hweight32/... macros when reading through some driver code in the kernel. I would like to understand, what these macros are for and what they are doing but unfortunately I failed to find any documentation on the topic.

The definition of the macros looks like this and can be found in
include/asm-generic/bitops/const_hweight.h

#define hweight8(w)  (__builtin_constant_p(w) ? __const_hweight8(w)  : __arch_hweight8(w))
#define hweight16(w) (__builtin_constant_p(w) ? __const_hweight16(w) : __arch_hweight16(w))
#define hweight32(w) (__builtin_constant_p(w) ? __const_hweight32(w) : __arch_hweight32(w))
#define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w))

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丑疤怪 2025-02-09 08:01:42

好的，找到答案！

Hewight函数似乎用于计数次数等于字节/单词中的1。我不完全理解用例，但是我找到了此代码在Linux nand驱动程序中使用它来检查块是否被删除（所有位均为1），同时接受一些要翻转的位。

示例调用：

hweight8(1)  --> 1
hweight8(2)  --> 1
hweight8(3)  --> 2
hweight8(4)  --> 1
hweight8(5)  --> 2
hweight8(6)  --> 2
hweight8(7)  --> 3
hweight8(8)  --> 1
and so on...

Ok, found the answer!

The hweight functions seem to be used for counting the number of bits equals 1 in a byte/word. I do not fully understand the use case but I have found this piece of code in the Linux NAND driver using it for checking if a block is erased (all bits are 1) while accepting some bits to be flipped.

Example calls:

hweight8(1)  --> 1
hweight8(2)  --> 1
hweight8(3)  --> 2
hweight8(4)  --> 1
hweight8(5)  --> 2
hweight8(6)  --> 2
hweight8(7)  --> 3
hweight8(8)  --> 1
and so on...

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