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| author | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-02-20 18:48:22 +0100 |
|---|---|---|
| committer | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-05-21 02:45:14 +0200 |
| commit | dc9a969bdba0d48d36daf104d39a1390cbd83847 (patch) | |
| tree | 66ae53e1cfb3eed161b129cabb669f498054fe9c /Documentation/sparse.txt | |
| parent | 6f8d77f7855833370228f75cb2a05dfbc651566f (diff) | |
| download | sparse-dev-dc9a969bdba0d48d36daf104d39a1390cbd83847.tar.gz | |
doc: move sparse.txt to markdown and rename it
The file 'sparse.txt' contains some explanation about the
differences between the attributes 'nocast' and 'bitwise'.
It's valuable information.
So convert it to markdown syntax and rename it to a more
self-explanatory name.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Diffstat (limited to 'Documentation/sparse.txt')
| -rw-r--r-- | Documentation/sparse.txt | 45 |
1 files changed, 0 insertions, 45 deletions
diff --git a/Documentation/sparse.txt b/Documentation/sparse.txt deleted file mode 100644 index 383376c0..00000000 --- a/Documentation/sparse.txt +++ /dev/null @@ -1,45 +0,0 @@ -Sparse -~~~~~~ - -__nocast vs __bitwise: - -__nocast warns about explicit or implicit casting to different types. - -HOWEVER, it doesn't consider two 32-bit integers to be different -types, so a __nocast 'int' type may be returned as a regular 'int' -type and then the __nocast is lost. - -So "__nocast" on integer types is usually not that powerful. It just -gets lost too easily. It's more useful for things like pointers. It -also doesn't warn about the mixing: you can add integers to __nocast -integer types, and it's not really considered anything wrong. - -__bitwise ends up being a "stronger integer separation". That one -doesn't allow you to mix with non-bitwise integers, so now it's much -harder to lose the type by mistake. - -So the basic rule is: - - - "__nocast" on its own tends to be more useful for *big* integers -that still need to act like integers, but you want to make it much -less likely that they get truncated by mistake. So a 64-bit integer -that you don't want to mistakenly/silently be returned as "int", for -example. But they mix well with random integer types, so you can add -to them etc without using anything special. However, that mixing also -means that the __nocast really gets lost fairly easily. - - - "__bitwise" is for *unique types* that cannot be mixed with other -types, and that you'd never want to just use as a random integer (the -integer 0 is special, though, and gets silently accepted iirc - it's -kind of like "NULL" for pointers). So "gfp_t" or the "safe endianness" -types would be __bitwise: you can only operate on them by doing -specific operations that know about *that* particular type. - -Generally, you want __bitwise if you are looking for type safety. -"__nocast" really is pretty weak. - -Reference: - -* Linus' e-mail about __nocast vs __bitwise: - - http://marc.info/?l=linux-mm&m=133245421127324&w=2 |