What does !!(x) mean in C (esp. the Linux kernel)?

Posted by Willi Ballenthin on Stack Overflow See other posts from Stack Overflow or by Willi Ballenthin
Published on 2010-03-26T22:08:48Z Indexed on 2010/03/26 22:23 UTC
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I've been reading through the Linux kernel (specifically, 2.6.11). I came across the following definition:

#define unlikely(x)     __builtin_expect(!!(x), 0)

(from linux-2.6.11/include/linux/compiler.h:61 lxr link)

What does !! accomplish? Why not just use (x)?

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Developer IT

What does !!(x) mean in C (esp. the Linux kernel)? - Developer IT

What does !!(x) mean in C (esp. the Linux kernel)?

c

gcc

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