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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 |