double exclamation mark meaning ?

[devendra.aaru]

On Thu, Dec 6, 2012 at 4:50 AM, Shraddha Kamat <sh2008ka at gmail.com> wrote:
> Hi,
>
> # define likely(x)  __builtin_expect(!!(x), 1)
> # define unlikely(x)    __builtin_expect(!!(x), 0)
>
> I see these !! in the above expressions. Please explain me the
> meaning of those double exclamations. What is their significance ?
>

this is c question, right, google is your friend

> -- Shraddha
>
>
>
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