Why !! (Double or not ?)

When reading the cache of each CPU page, you can see the following:Code:

Static inlinestruct page * buffered_rmqueue (struct zone * preferred_zone, struct zone * zone, int order, gfp_t gfp_flags, int migratetype) {int cold = !! (Gfp_flags & _ gfp_cold );

Why !! What about it?

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It is said that the C/C ++ compiler thinks that: 0 is false, 1 is true, and that non-0 (except 1) is also true, and non-0 is 0, non-non-0 is 1. Why !! (X) processing, I think it should be caused by data truncation during type conversion. For example, the parameter in if () is int, but X is long. If X is 0x11111111 00000000, it is true, but if (x, it may be truncated to 0 if (!! (X.