From 9cc01abd43e3950a7c4da2b01a8851fd48dfa3b0 Mon Sep 17 00:00:00 2001 From: Luc Van Oostenryck Date: Sat, 1 Aug 2020 02:45:55 +0200 Subject: doc: replace nocast-vs-bitwise document with its lore link The nocast-vs-bitwise document was copied here to be sure to remain accessible but isn't really useful here now because: 1) the original document have also been archived to lore.kernel.org 2) nocast & bitwise have now been documented 3) 2) contains a link to 1) So, remove this redundant document. Signed-off-by: Luc Van Oostenryck --- Documentation/index.rst | 1 - Documentation/nocast-vs-bitwise.md | 43 -------------------------------------- 2 files changed, 44 deletions(-) delete mode 100644 Documentation/nocast-vs-bitwise.md diff --git a/Documentation/index.rst b/Documentation/index.rst index 9c76419b..cbe0521b 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -69,7 +69,6 @@ User documentation :maxdepth: 1 annotations - nocast-vs-bitwise Developer documentation ----------------------- diff --git a/Documentation/nocast-vs-bitwise.md b/Documentation/nocast-vs-bitwise.md deleted file mode 100644 index 9ba5a789..00000000 --- a/Documentation/nocast-vs-bitwise.md +++ /dev/null @@ -1,43 +0,0 @@ -__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 - 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`: - - -- cgit 1.2.3-korg