Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 21 Jun 2012 19:22:30 -0700 | Subject | Re: [patch 3.5-rc3] mm, mempolicy: fix mbind() to do synchronous migration |
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On Thu, Jun 21, 2012 at 6:45 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > And casts to/from bool, perhaps. To squish the warning we'd do things > like a_bool = !!a_int. That generates extra code, but gcc internally > generates extra code for a_bool = a_int anyway, and a quick test here > indicates that the generated code is identical (testl/setne).
It *has* to generate extra code. A cast to Bool is very much not at all like a normal cast. All the traditional C casts just do a pure bit truncate (or zero/sign extension) keeping the same value.
A cast to bool is totally different. It is exactly the same as "test against zero" - so it in no way acts like a traditional integer cast to a one-bit integer.
I'm not 100% sure the use of "bool" is a great idea, and people who use pointers to bools are crazy mf's (you can break the fundamental property of bools by assigning random values through the pointer), but _Bool certainly ahs the _potential_ to be a good thing. The reason I'm nervous about it is exactly that people get it wrong so easily because they do *not* act like any other C type (the whole pointer-to-bool thing being one example of people doing bad things - I personally would be much happier if _Bool acted more like a one-bit bitfield and could not have its address taken).
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