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{un}likely macros?

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Hi there people,
first of all i would like to thank everybody for their help in figuring out 
the yesterday's asm oneliner. I have another q, though :)
The kernel extensively uses these macros. 

<from include/linux/compiler.h,45>
45 #define likely(x)       __builtin_expect(!!(x), 1)
46 #define unlikely(x)     __builtin_expect(!!(x), 0)

As far as I understand it, they evaluate to something only when the compiler's 
minor number is < 96:

<from include/linux/compiler-gcc2.h,11>
 11 #if __GNUC_MINOR__ < 96
 12 # define __builtin_expect(x, expected_value) (x)
 13 #endif

otherwise they evalute to nothing(?). However, what i don't understand is, 
what do i accomplish by negating a value twice (!!(x)). I read somewhere on 
the kernel mailing list that it had something to do with pointer conversion 
but the context of the message was rather different so i think that this 
might not hold true.

Thanks in advance,
Boris.
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